Sunday, April 26, 2009

Thermocouple Theory

Thermocouple Theory
By Caleb Streur


A thermocouple is a commonly used type of sensor that is used to measure temperature. Thermocouples are popular in industrial control applications because of their relatively low cost and wide measurement ranges. In particular, thermocouples excel at measuring high temperatures where other common sensor types cannot function. Try operating an integrated circuit (LM35, AD 590, etc.) at 800C.

Thermocouples are fabricated from two electrical conductors made of two different metal alloys. The conductors are typically built into a cable having a heat-resistant sheath, often with an integral shield conductor. At one end of the cable, the two conductors are electrically shorted together by crimping, welding, etc. This end of the thermocouple--the hot junction--is thermally attached to the object to be measured. The other end--the cold junction, sometimes called reference junction--is connected to a measurement system. The objective, of course, is to determine the temperature near the hot junction.

It should be noted that the "hot" junction, which is somewhat of a misnomer, may in fact be at a temperature lower than that of the reference junction if low temperatures are being measured.

Reference Junction Compensation Thermocouples generate an open-circuit voltage, called the Seebeck voltage, that is proportional to the temperature difference between the hot and reference junctions :

Vs = V(Thot-Tref)

Since thermocouple voltage is a function of the temperature difference between junctions, it is necessary to know both voltage and reference junction temperature in order to determine the temperature at the hot junction. Consequently, a thermocouple measurement system must either measure the reference junction temperature or control it to maintain it at a fixed, known temperature.

There is a misconception of how thermocouples operate. The misconception is that the hot junction is the source of the output voltage. This is wrong. The voltage is generated across the length of the wire. Hence, if the entire wire length is at the same temperature no voltage would be generated. If this were not true we connect a resistive load to a uniformly heated thermocouple inside an oven and use additional heat from the resistor to make a perpetual motion machine of the first kind.

The erroneous model also claims that junction voltages are generated at the cold end between the special thermocouple wire and the copper circuit, hence, a cold junction temperature measurement is required. This concept is wrong. The cold -end temperature is the reference point for measuring the temperature difference across the length of the thermocouple circuit.

Most industrial thermocouple measurement systems opt to measure, rather than control, the reference junction temperature. This is due to the fact that it is almost always less expensive to simply add a reference junction sensor to an existing measurement system than to add on a full-blown temperature controller. Sensoray Smart A/D's measure the thermocouple reference junction temperature by means of a dedicated analog input channel. Dedicating a special channel to this function serves two purposes: no application channels are consumed by the reference junction sensor, and the dedicated channel is automatically pre-configured for this function without requiring host processor support. This special channel is designed for direct connection to the reference junction sensor that is standard on many Sensoray termination boards.

Linearization Within the "useable" temperature range of any thermocouple, there is a proportional relationship between thermocouple voltage and temperature. This relationship, however, is by no means a linear relationship. In fact, most thermocouples are extremely non-linear over their operating ranges. In order to obtain temperature data from a thermocouple, it is necessary to convert the non-linear thermocouple voltage to temperature units. This process is called "linearization."

Several methods are commonly used to linearize thermocouples. At the low-cost end of the solution spectrum, one can restrict thermocouple operating range such that the thermocouple is nearly linear to within the measurement resolution. At the opposite end of the spectrum, special thermocouple interface components (integrated circuits or modules) are available to perform both linearization and reference junction compensation in the analog domain. In general, neither of these methods is well-suited for cost-effective, multipoint data acquisition systems.

In addition to linearizing thermocouples in the analog domain, it is possible to perform such linearizations in the digital domain. This is accomplished by means of either piecewise linear approximations (using look-up tables) or arithmetic approximations, or in some cases a hybrid of these two methods.

The Linearization Process Sensoray’s Smart A/D’s employ a thermocouple measurement and linearization process that is designed to hold costs to a practical level without sacrificing performance.

First, both the thermocouple and reference junction sensor signals are digitized to obtain thermocouple voltage Vt and reference junction temperature Tref. The thermocouple signal is digitized at a higher rate than the reference junction because it is assumed that the reference junction is relatively stable compared to the hot junction. Reference junction measurements are transparently interleaved between thermocouple measurements without host processor intervention.

An onboard processor then performs linearization and reference junction compensation in the digital domain. Depending on the thermocouple type being used, an appropriate "correction voltage" is computed by mapping reference junction temperature into equivalent thermocouple voltage: Vc=V(Tref). This correction voltage is added to the measured thermocouple voltage to obtain the "corrected" thermocouple voltage:Vtc=Vt+Vc. Finally, the corrected thermocouple voltage is linearized by mapping it into temperature units: T=T(Vtc). Sensoray Smart Sensor Processors utilize look-up tables for determination of both correction voltage and thermocouple temperature. Although there are many advantages to this approach, the most important is this: high measurement throughputs can be achieved without the need for a high-speed DSP. Consequently, Smart A/D’s offer superior thermocouple measurement performance at a low cost and low power-consumption..

Article Source: _

Triple Point of Hydrogen 13.81 -259.34
Liquid/Vapor Phase of Hydrogen 17.042 -256.108
at 25/76 Std. Atmosphere
Boiling Point of Hydrogen 20.28 -252.87
Boiling Point of Neon 27.102 -246.048
Triple Point of Oxygen 54.361 -218.789
Boiling Point of Oxygen 90.188 -182.962
Triple Point of Water 273.16 0.01
Boiling Point of Water 373.15 100
Freezing Point of Zinc 692.73 419.58
Freezing Point of Silver 1235.08 961.93
Freezing Point of Gold 1337.58 1064.43

Saturday, April 25, 2009

Basic Thermocouples

How Does A Thermocouple Work?
By Joe Crew


Measurement and control of temperature is one of the most common requirements of industrial instrumentation and the thermocouple is by far the most widely used temperature sensor. Its characteristics include good inherent accuracy, suitability over a broad temperature range, fast thermal response, ruggedness, high reliability and low cost.

How does a thermocouple work?

T.J Seebeck discovered in the 1820s that an electric current flows in a closed circuit of two dissimilar metals when one of the two junctions is heated with respect to the other. In a thermocouple circuit the current continues to flow as long as the two junctions are at different temperatures. The magnitude and direction of the current depends on the temperature difference between the junctions and the properties of the metals used in the circuit. This is known as the Seebeck effect. Click here to see an example of the circuit.

If the circuit is broken at the center, the net open circuit voltage (the Seebeck voltage) is a function of the junction temperature and the composition of the two metals.

If the hot and cold junctions are reversed, current will flow in the opposite direction. Any two dissimilar metals can be used and the thermocouple circuit will generate a low voltage output that is almost (but not exactly) proportional to the temperature difference between the hot junction and the cold junction. The voltage output is between 15 and 40µV per degree C, dependant on the thermocouple conductor metals used. The actual metals used in industrial thermocouples depend on the application and temperature measurement range required.

Thermocouple failure prediction

Like any other metal object, thermocouples are subject to metal fatigue wear and tear; they have a finite life. Many users of thermocouples are not aware of thermocouple deterioration until the sensor breaks, often causing an expensive interruption of a process. Removing a thermocouple from a furnace when at operating temperature can be difficult and dangerous. In fact the thermocouple, a simple and generally inexpensive sensor, can cause inaccurate readings for some time before any errors are detected. The errors usually cause low readings due to the thermocouple wires becoming thinner.

Impurities induced by any handling during manufacture or installation can accelerate chemical deterioration of the thermocouple. For base metal thermocouples, deterioration occurs slowly due to contact with the atmosphere, which in turn causes oxidation. As the surface of the thermocouple wires oxidises the current carrying cross sectional area is reduced. Nobel metal thermocouple deterioration is also well documented.

In "Principals and Method of Temperature Measurement", Thomas D McGee explains that the usual result of deterioration is the gradual reduction in the Seebeck voltage, often extended over several weeks and not frequently detected. If the Seebeck voltage is low, the measured temperature will also be low, so the actual process temperature will be increased to produce the required Seebeck voltage. The net result will be excessive temperature generation with resulting damage to material and processes. Those who use thermocouples should be aware of the possibilities of slow deterioration and its consequences.

A temperature controller, for example, would actually compensate for the thermocouple's loss of thermoelectric power by putting more heat into the process with all the energy, environmental and process plant costs that would be incurred. Fortunately, while Mr Thomas Johann Seebeck was experimenting with his wires in the 1820s, his contemporary and fellow countryman, Mr Georg Ohm, was also conducting his own experiments. Fortuitously because as the thermocouple conductors become thinner, their resistance changes as described in "Practical Temperature Measurement" by Peter R. N. Childs.

"The loop resistance of a thermocouple depends on its length, type and diameter of the thermocouple wire, the length type and diameter of extension wires, temperatures along the circuit and the contact resistance at any connections. If on installation, and at regular intervals in use, a measurement is made of this loop resistance, then a change in this value can be used to indicate wire thinning due to chemical attack, loose or corroded connections, contact resistance due to broken but touching wires or electrical shunting due to loss of insulation at some location along the wire."

Regular measurements of the thermocouple loop can indicate that the sensor should be replaced for reasons of accuracy and can also be used to predict its complete failure (sensor break). As thermocouple conductors oxidise they become brittle, making them more susceptible to breakage due to bending or vibration. Replacing thermocouples during a planned maintenance period is easier and more cost effecting than replacing thermocouples while the plant is running.

Joe Crew is the Product Manager at Data Track Process Instruments Ltd. Data Track manufactures digital panel meters, large number displays, PID controllers, signal conditioners and remote data acquisition systems for the process and control industry. Data Track can also supply HMI touchscreen operator panels and SCADA software. In their new line of PID controllers, Data Track has developed a solution to this common thermocouple problem. The Tracker 331 and Tracker 332 have, as standard, the ability to continually measure the condition of the connected thermocouple and prompt for its replacement before it starts to affect the process and/or fails completely.

Article Source: _

The Seebeck effect
The discovery of thermoelectricity dates back to Seebeck [
1] (1770-1831). Thomas Johann Seebeck was born in Revel (now Tallinn), the capital of Estonia which at that time was part of East Prussia. Seebeck was a member of a prominent merchant family with ancestral roots in Sweden. He studied medicine in Germany and qualified as a doctor in 1802. Seebeck spent most of his life involved in scientific research. In 1821 he discovered that a compass needle deflected when placed in the vicinity of a closed loop formed from two dissimilar metal conductors if the junctions were maintained at different temperatures. He also observed that the magnitude of the deflection was proportional to the temperature difference and depended on the type of conducting material, and does not depend on the temperature distribution along the conductors. Seebeck tested a wide range of materials, including the naturally found semiconductors ZnSb and PbS. It is interesting to note that if these materials had been used at that time to construct a thermoelectric generator, it could have had an efficiency of around 3% - similar to that of contemporary steam engines.
The Seebeck coefficient is defined as the open circuit voltage produced between two points on a conductor, where a uniform temperature difference of 1K exists between those points

Thursday, April 23, 2009

Work and Kinds of Accelerometer

How does an Accelerometer Work?
By Bob Jonathan


An accelerometer is an instrument for measuring acceleration, detecting and measuring vibrations, or for measuring acceleration due to gravity (inclination). Accelerometers can be used to measure vibration on vehicles, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, inclination, machine vibration, dynamic distance and speed with or without the influence of gravity.


Used for calculating acceleration and measuring vibrations, the accelerometer is capable of detecting even the slightest movements, from the tilting of a building to smallest vibration caused by a musical instrument. Inside the accelerometer sensor minute structures are present that produces electrical charges if the sensor experiences any movement.
Accelerometers need to be placed on the surface of the object in order to determine the vibrations. It is not capable of work in isolation or apart from the object it is required to assess, it must be firmly attached to the object in order to give precise readings.


The two kinds of basic accelerometers are:


At times Inputs and output readings also matter especially when it comes to determining the kind of accelerometer that needs to be placed on a certain object. If the output is digital then a digital accelerometer must be placed and vice versa. The main feature of this accelerometer is that the output tends to change when there is even a slight change in the input.
The most common type of this accelerometer is used in airbags of automobiles, to note the sudden drop in the speed of the vehicle and to trigger the airbag release. Even laptops are now being equipped with accelerometers in order to protect the hard drive against any physical dangers, caused mainly due to accidental drops.


The digital accelerometer is more sophisticated than the analog. Here the amount of high voltage time is proportional to the acceleration. One of its major advantages is that it is more stable and produces a direct output signal. Accelerometers are now also used in aerospace and many military applications, such as missile launch, weapon fire system, rocket deployment etc. Many a times these accelerometers are used to protect fragile equipment during cargo transportation, and report any strain that might cause a possible damage. Some companies have also managed to develop a wireless 3-axis accelerometers which are not only low in cost but are also shock durable. This 3-axis accelerometer has sensors that are used to protect mobiles and music players. Also these sensors are used in some of the devices used for traffic navigation and control.


Depending upon the kind of work, the accelerometers vary in the way they are prepared and how they work. Some accelerometers use piezoelectricity, these are man-made. In such accelerometers the acceleration is calculated based upon the charges derived from the microscopic crystalline structures when they are accelerated due to motion.


Another kind works with the capacitance and the changes initiated within it as a result of some accelerative force. This technology is used from automotive industry to agriculture industry and from NASA to military researches and operations.


This device is used to measure strain in an object, which is detected by a foil strain element. If the object, to which the gauge is attached is some how deformed that creates electrical charges and is known as the gauge factor.



Due to high demand and wide spread use of accelerometers in the automotive industry and new hi-tech technology, these sensors are now light weight and are available at low cost and reduced prices.


Microphones also carry accelerometers. That is how they are able to detect the minute frequencies.


The forces that can cause vibrations which are detected by the accelerometer can be static, dynamic or gravitational. Certain accelerometers are rated G. G stands for Gravity. Such accelerometers are used mostly in robotics. They are more sensitive to motion and can be triggered at the slightest changes in gravitational pulls.

Read more about Accelerometer.

copyrights -

Article Source:

Memsic 2125 Accelerometer Demo Kit
Acceleration, Tilt, and Rotation Measurement

The Memsic 2125 is a low cost, dual-axis thermal accelerometer capable of measuring dynamic acceleration (vibration) and static acceleration (gravity) with a range of ±2 g. For integration into existing applications, the Memsic 2125 is electrically compatible with other popular accelerometers. What kind of things can be done with the Memsic 2125 accelerometer? While there are many possibilities, here’s a small list of ideas that can be realized with a Memsic 2125 and the Parallax BASIC
Stamp® microcontroller:

- Dual-axis tilt sensing for autonomous robotics applications (BOE-Bot, Toddler, SumoBot)
- Single-axis rotational position sensing
- Movement/Lack-of-movement sensing for alarm systems

Memsic 2125 Datasheet pdf

2g Tri-Axis Digital Accelerometer
The KXP84-2050 is a tri-axis silicon micromachined accelerometer with a full-scale output range of ±2g (19.6m/s2). The sense element is fabricated using Kionix’s proprietary plasma micromachining process technology. Acceleration sensing is based on the principle of a differential capacitance arising from acceleration-induced motion of the sense element, which further utilizes common mode cancellation to decrease errors from process variation, temperature, and environmental stress.

KXP84-2050 Datasheet

Wednesday, April 22, 2009

Basic Fiber Optic Sensors

Absolute Beginners' Guide to Fiber Optic Sensors
By Colin Yao

What are fiber optic sensors?

The fundamental characteristic of all fiber optic sensors is that they depend on some optical properties, such as intensity, phase, state of polarization and wavelength, to be modulated by measurands. Measurands could be pressure, temperature, electromagnetic field or displacement.

All fiber optic sensors have an optical element that is sensing these property changes. For most sensors, this element is the optical fiber itself or a non-fiber optical element.

Fiber optic sensors with optical fiber as sensor element are called "intrinsic fiber sensor" and sensors with a non-optical fiber sensing element are called "extrinsic fiber sensor".

1. Intrinsic Fiber Sensors

In the intrinsic fiber sensor, external measurands such as pressure, vibration, temperature interact with optical fiber element and cause fiber bending, fiber distortion and a change in the refractive index of the sensing fiber.

Because of the refractive index change, lights that travel through the fiber are affected accordingly. The changes in light properties, such as light intensity, light wavelength and light phase are then detected. The magnitude of measurands interacting with the fiber can then be determined.

2. Extrinsic Fiber Sensors

Birefringent crystal, intensity mask or thin film absorbers are most often used as sensor elements in extrinsic fiber sensors. Usually they are integrated into the optical path.

When the external force interacts with the sensing element, the light properties are modulated as well. The sensor has light source, optical path and photo detector parts. The magnitude of measurands is detected similar to intrinsic fiber sensors.

The Applications of Fiber Optic Sensors

Wide Area Sensing and Monitoring

Because of optical fiber's immune to electromagnetic field, fiber sensors have a big potential in these areas. They are widely used in temperature sensing in building, leakage monitoring along oil pipelines and so on.

The above mentioned applications are called wide area sensing or monitoring. The name means that the sensing covers a wide area. In this area, fiber sensors are divide into two categories: distributed sensor and quasi-distributed sensor.

1. Distributed Sensor

Distributed sensors sense measurands continuouly over the entire length of the fiber. The most important criteria is that sensor fibers must be very sensitive to measurands.

A typical example of distributed sensors is a temperature sensor utilizing Raman scattering effect in optical fibers. Another example is OTDR (Optical Time Domain Reflectometer) which senses signal reflection in the whole length of an optical path.

2. Quasi-Distributed Sensor

Quasi-distributed sensors use discrete sensor elements that are carefully arranged in the fiber network. This type if sensor needs to be small size, low cost and high reliability.

High Sensitivity Measurements

Another area for fiber sensors is the high sensitivity measurement applications. This type of sensors typically utilize light interference's extremely high sensitivity property.

A number of interferometric fiber sensors have been used for measurement of temperature, pressure, vibration and so on. The fiber optic gyroscope is one typical example of this type of applications.

Harsh Environment Measurement

Some extreme environment has no choice but fiber optic sensors. This kind of applications include high temperature, immersion into chemical reagents, radioactive rays factories and so on. The fiber optic sensor's resistant to this type of harsh environment is extremely important.

Colin Yao is an expert on fiber optic communication technologies and products. Learn about fiber optic ST, ST connectors, ST fiber connector on Fiber Optics For Sale Co. web site.

Article Source: _

Overview of Fiber Optic Sensors
Over the past twenty years two major product revolutions have taken place due to the
growth of the optoelectronics and fiber optic communications industries. The
optoelectronics industry has brought about such products as compact disc players, laser printers, bar code scanners and laser pointers. The fiber optic communication industry has literally revolutionized the telecommunication industry by providing higher performance, more reliable telecommunication links with ever decreasing bandwidth cost. This revolution is bringing about the benefits of high volume production to component users and a true information superhighway built of glass.
more pdf

Fiber Optic Sensors Device



Monday, April 20, 2009

Emergency Wireless Sensor Networks

Wireless Sensor Networks - An Emerging Technology
By Udit Agarwal

Wireless sensor networks (WSNs) are an emerging technology consisting of small, low-power devices that integrate limited computation, sensing and radio communication capabilities. The technology has the potential to provide flexible infrastructures for numerous applications, including healthcare, industry automation, surveillance and defense. Wireless sensor networks promise an unprecedented fine-grained interface between the virtual and physical worlds. They are one of the most rapidly developing new information technologies, with applications in a wide range of fields including industrial process control, security and surveillance, environmental sensing, and structural health monitoring.

A wireless sensor network is a wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. The development of wireless sensor networks was originally motivated by military applications such as battlefield surveillance. However, wireless sensor networks are now used in many civilian application areas, including environment and habitat monitoring, healthcare applications, home automation, and traffic control.

In addition to one or more sensors, each node in a sensor network is typically equipped with a radio transceiver or other wireless communications device, a small micro controller, and an energy source, usually a battery. The envisaged size of a single sensor node can vary from shoebox-sized nodes down to devices the size of grain of dust, although functioning 'motes' of genuine microscopic dimensions have yet to be created. The cost of sensor nodes is similarly variable, ranging from hundreds of dollars to a few cents, depending on the size of the sensor network and the complexity required of individual sensor nodes. Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and bandwidth. A sensor network normally constitutes a wireless ad-hoc network, meaning that each sensor supports a multi-hop routing algorithm (several nodes may forward data packets to the base station). In computer science and telecommunications, wireless sensor networks are an active research area with numerous workshops and conferences arranged each year.

The applications for WSNs are many and varied. They are used in commercial and industrial applications to monitor data that would be difficult or expensive to monitor using wired sensors. They could be deployed in wilderness areas, where they would remain for many years (monitoring some environmental variables) without the need to recharge/replace their power supplies. They could form a perimeter about a property and monitor the progression of intruders (passing information from one node to the next). There are many uses for WSNs. Typical applications of WSNs include monitoring, tracking, and controlling. Some of the specific applications are habitat monitoring, object tracking, nuclear reactor controlling, fire detection, traffic monitoring, etc. In a typical application, a WSN is scattered in a region where it is meant to collect data through its sensor nodes. Another class of application is the so-called smart space.

Article Source: _

Wireless Sensor NetworkBased Tunnel Monitoring
In this paper we describe the development and deployment of a
wireless sensor network (WSN) to monitor a train tunnel during adjacent
construction activity. The tunnel in question is a part of the
London Underground system. Construction of tunnels beneath the
existing tunnel is expected to cause deformations. The expected deformation
values were determined by a detailed geotechnical analysis.
A real-time monitoring system, comprising of 18 sensing units
and a base-station, was installed along the critical zone of the tunnel
to measure the deformations. The sensing units report their data
to the base-station at periodic intervals. The system was used for
making continuous measurements for a period of 72 days. This
window of time covered the period during which the tunnel boring
machine (TBM) was active near the critical zone. The deployed
WSN provided accurate data for measuring the displacements and
this is corroborated from the tunnel contractor’s data.

More pdf

Saturday, April 18, 2009

Speed Sensors of Turbine

Turbine Speed Sensors - When RPM Counts
By Rosa Telip Ten

With turbine technology finding its way into more and more aspects of todays high tech world, many people just like yourself may find themselves in uncharted water in having to deal with them. The fact is, that turbines can be simple or extremely complex depending on what they are used in.

A Complex Turbine

For instance, a modern jet will have a highly complex turbine engine that burns fuel inside a series of alloy fan bladed to generate thrust. This would be a highly complex example of a turbine system being used to generate kinetic energy and force.

A Simple Turbine Engine

At the same time, the simple spinning vent on the roof of a house is yet another example of a far more simpler turbine engine. Even though it has only one moving part, it is by definition, a turbine engine none the less. Heat in the attic carries the energy that powers the roof vent turbine to spin, causing it to suck air out of the attic, thereby ventilating it.

Turbine Speed Indicators

A turbine speed sensor is but one of the many types of sensors that would be found on a complex turbine engine. Why is it necessary to know the speed that a turbine in an engine is spinning? If the engine is a jet engine, the the turbine is the main power source and the speed that it is rotating would be a prime indicator propulsion.

Turbo Charged Air Intake Systems

Also, a turbine can be an integral part but not the main component of a propulsion system or engine. A prime example of this would be a car with a turbo charged intake system. In this case a turbine speed sensor would provide real time information on how the air intake system is functioning at any given time.

Article by Rosa Telipten. Here you will find everything you wanted to learn regarding Turbine Speed Sensor and even Magnetic Speed Sensors

Article Source: _

Real-Time Optical Fuel-to-Air Ratio
Sensor for Gas Turbine Combustors

The measurement of the temporal distribution of fuel in gas turbine
combustors is important in considering pollution, combustion
efficiency and combustor dynamics and acoustics. Much of the
previous work in measuring fuel distributions in gas turbine
combustors has focused on the spatial aspect of the distribution.
The temporal aspect however, has often been overlooked, even
though it is just as important. In part, this is due to the challenges
of applying real-time diagnostic techniques in a high pressure
and high temperature environment. A simple and low-cost instrument
that non-intrusively measures the real-time fuel-to-air ratio (FAR) in
a gas turbine combustor has been developed. The device uses a dual
wavelength laser absorption technique to measure the concentration
of most hydrocarbon fuels such as jet fuel, methane, propane, etc. The
device can be configured to use fiber optics to measure the local FAR
inside a high pressure test rig without the need for windows. Alternatively,
the device can readily be used in test rigs that have existing windows
without modifications. An initial application of this instrument was
to obtain time-resolved measurements of the FAR in the premixer of a
lean premixed prevaporized (LPP) combustor at inlet air pressures and
temperatures as high as 17 atm @ 800 K, with liquid JP-8 as the fuel.
Results will be presented that quantitatively show the transient nature
of the local FAR inside a LPP gas turbine combustor at actual operating
conditions. The high speed (kHz) time resolution of this device, combined
with a rugged fiber optic delivery system, should enable the realization of a
flight capable active-feedback and control system for the abatement of
noise and pollutant emissions in the future. Other applications that
require an in-situ and time-resolved measurement of fuel vapor
concentrations should also find this device to be of use.

More pdf

Friday, April 17, 2009

Basic of Ultrasonic Flow Meter and Device

Ultrasonic Flow Meter

– Some Basic Principles

Author: Jim Furness

Ultrasonic flow meter technology has much improved over the last few years and now forms a viable flow measurement technique compared to other methods such as turbine and electromagnetic type systems. The first Doppler ultrasonic flow meter units became available in the early 70’s. To begin with, as with all new technologies they were not very accurate, difficult to install and costly. However, the newest Time of Flight ultrasonic flow meter and Doppler types are proving to be both reliable and accurate. Accuracy has improved significantly with most ultrasonic flow meter manufacturers claiming 0.5% accuracy if the meters are correctly installed.

With these two technologies, which ultrasonic flow meter should you use?

Although Doppler ultrasonic flow meters use an older technology, they are ideal for liquids with air bubbles or slurries with significant solid particles. They determine the flow using the Doppler shift method, by measuring the change in frequency created by an object moving towards, or away from the measurement point. Normally liquids with a minimum of 100ppm concentration at 100microns particle size or bigger would be suitable for a Doppler ultrasonic flow meter. One stumbling block of most Doppler ultrasonic flow meter systems is that they are less accurate in low flow conditions.

A transit time ultrasonic flow meter is ideal for clean fluids such as water and oil. These meters are more advanced than Doppler ultrasonic flow meter types due to the advanced calculations used to determine the flow rate. Two transducers are used, the first sends an acoustic signal which is bounced off of the bottom of the pipe, the second transducer receives the signal. The ultrasonic flow meter is then able to determine flow by calculating the time it takes to receive the signal.

Portable ultrasonic flow meter kits are now available for plant wide surveys with minimal fuss and no down time. The first portable ultrasonic flow meter units were heavy and quite large, basically a luggable design. As ultrasonic flow meter design has improved over time, the instruments have become much smaller, lighter and more power efficient and are truly hand portable. Also many ultrasonic flow meter models now have integral data loggers, allowing the user to leave the meter on site so it can record average flow rates and flow totals.

An ultrasonic flow meter will be most accurate when fitted on a long, straight piece of pipe, free from obstructions such as elbows and valves. Also, any rusty pipes should be cleaned before using an ultrasonic flow meter. Ultrasonic jelly should also be smeared under the sensor to ensure a solid contact on the pipe.

The biggest advantage to using an ultrasonic flow meter is maintenance. Older insertion meters usually require the plant to be shut down while installing. However an ultrasonic flow meter can be installed without stopping the process. Also as an ultrasonic flow meter has no moving parts it cannot wear out.

Both Doppler and transit time portable ultrasonic flow meter kits are available from Omni Instruments for hire or purchase.

By Richard Burgess

About the Author:

Jim Furness is CEO of Omniinstruments Ltd, specialists in data logger and other instrumentation solutions such as Ultrasonic Flow Meter.

Article Source:

The DMTF wall-mount Clamp-on Ultrasonic Flow meter family provides abundant capabilities for accurate liquid flow measurement from outside of a pipe. It utilizes state-of-the-art technologies on ultrasonic transmission /receiving, digital signal processing and transit-time measurement. The proprietary signal quality tracking and self-adapting technologies allow system to optimally adapt to different pipe materials automatically.


Wednesday, April 15, 2009

Infrared Motion Sensor

Infrared Sensor

Author: coration

Sensors are everywhere, some examples:

  • Smaller shops or barbershops, often have a beam of light crossing the room near the door, which ends up in a photo-sensor on the other side of the room. When a customer breaks that beam, the bell rings.

  • Bigger markets have automated doors, the black bulb above the door sends a burst of microwave radio energy, and waits for the reflected energy to bounce back. When a person walks into that field, the amount of energy is changed,...resulting in the door to open. Therefor you can't just run in a market, the doors wont open fast enough ;). So no kidz, it doesn't have a little leprecon in it, which presses a button to open the doors!!

  • Same thing with ultrasonic sound waves used by bats for example, they bounce back off a target and create an image.
    These are what we call active sensors. They send out energy, and detect changes in them .

Motion Sensor

The motion sensing system is a passive sensor. It detects infrared energy. Human beings have a skin temperature of approximately 36° Celsius or 93° Fahrenheit, this produces an infrared energy with a wavelength between 9 and 10 micrometers. When infrared energy is detected, that infrared light bumps electrons of the sensors substrate, these are amplified and result in a signal.
People who have these little sensors, may notice that the sensing light doesn't go off when you're standing still. That's because the sensor is programmed to sense rapidly changes, you don't want every change of infrared light setting off the alarm .

If you're searching for a hack in this system, ...than this is your lucky day, because you can. The sensors are sensitive in a range of 8 - 12 micrometers. So all you need to do is calculate what body temperature you got to have to produce waves of 7 micrometers or less. I'm not responsible if you got hypothermia afterwards ;) . Or maybe you could build a glass bulb around you, glass doesn't let the infrared waves through, think of a greenhouse, the light goes in , but then it's trapped inside... so beware of people passing by in the possession of glass bulbs...

Footnote: During Operation: Desert Storm. The US military used infrared vision equipped tanks to spot and fight hostile tanks at night. Result: hostile tanks getting slaughtered like a sitting duck, technology = win

About the Author:

I'm Jan Vansteenlandt, i'm 19 years old, i still attend school.

My articles will be around the technology topic, and all it's subcategories. Normally IT-related.

I hope you enjoy them :)

Article Source:

Infrared Sensor Device

The Model DXT-54 Passive ILinear DXT-54 Passive Infrared Motion Detector Transmitternfrared Motion Detector Transmitter is a battery powered passive infrared motion detector with a built-in transmitter designed for use with Linear's DX format receivers. This transmitter can be used in a variety of motion detection applications. When the passive infrared sensor detects motion in its field of view, the transmitter sends a digitally coded wireless signal to its companion receiver.


Bye Bye Standby Energy Saving Motion Sensor
Save money and energy: switch off your home as you walk out of the room with the Bye Bye Standby Energy Saving Motion Sensor. This PIR (Passive Infrared) Motion sensor can be used in conjunction with the Bye Bye Standby® Smart Sockets to give appliance co


Tuesday, April 14, 2009

Motion Sensor Lights

Motion Sensor Lights - Why You Need a Detector Light Outdoors
By Amanda Taylor

Have you seen outdoor lights that only come on when they detect movement? These special fixtures are called motion sensor lights and they offer many advantages to a homeowner.

Outdoor sensor lighting is a natural intruder deterrent. This is one of the biggest reasons that people decide to install motion sensor lights. Burglars do not like to come to a home that is well lit, or one that becomes lit when they approach it. Motion detector lights are one of the best ways to provide safety and security to your family without investing in an alarm system.

Motion sensor lights are energy efficient. If typical outdoor fixtures are left on all night every night, you will notice a difference in your electric bill. With motion sensor outdoor lighting, however, there is only a small or even unnoticeable increase in your electricity bill because the light fixture is mostly off. So, not only do you get added security, you also get cost savings!

Motion detector lights can be decorative as well as functional. Many of the first fixtures were not very decorative, but now there are many different styles, sizes, and colors available that are designed to compliment different homes. For most of the fixtures, there is no way to tell if they are “regular” or sensor.

Motion sensor lights can be customized and programmed. To learn more about different settings of motion sensor outdoor lights, visit this website:

For all the benefits it has to offer, motion sensor lights are a good choice for your home.

Click on the link to learn more about []motion sensor lights. They come in a variety of sizes and shapes. They can be made to fit in just about any outdoor area and can be purchased online. Click on the link to get all the facts and info about outdoor lighting at

Article Source:

PIR Motion Sensor
Description: This is a simple to use motion sensor. Power it up and wait 1-2 seconds for the sensor to get a snapshot of the still room. If anything moves after that period, the 'alarm' pin will go low.Red wire is power (5 to 12V). Brown wire is GND. Black wire is open collector Alarm.This unit works great from 5 to 12V (datasheet shows 12V). You can also install a jumper wire past the 5V regulator on board to make this unit work at 3.3V. Sensor uses 1.6mA@3.3V.The alarm pin is an
open collector meaning you will need a pull up resistor on the alarm pin. The open drain setup allows multiple motion sensors to be connected on a single input pin. If any of the motion sensors go off, the input pin will be pulled low.The connector is slightly odd but has a 0.1" pitch female connector making it compatible with jumper wires and 0.1" male headers.


Monday, April 13, 2009

Sensors in Industrial Applications

A Role of Sensors for Industrial Applications

Author: s.sankar

Since a significant change involves an exchange of energy, sensors can be classified according to the type of energy transfer that they detect. Thermal temperature sensors: thermometers, thermocouples, temperature sensitive resistors (thermistors and resistance temperature detectors), bi-metal thermometers and thermostats

heat sensors: bolometer, calorimeter

Electromagnetic electrical resistance sensors: ohmmeter, multimeter

Electrical current sensors: galvanometer, ammeter

Electrical voltage sensors: leaf electroscope, voltmeter

Electrical power sensors: watt-hour meters

Magnetism sensors: magnetic compass, fluxgate compass, magnetometer, Hall Effect device,

Metal detectors

Mechanical pressure sensors: altimeter, barometer, barograph, pressure gauge, air speed indicator, rate of climb indicator, variometer

gas and liquid flow sensors: flow sensor, anemometer, flow meter, gas meter, water meter, mass flow sensor mechanical sensors: acceleration sensor, position sensor, selsyn, switch, strain gauge

Chemical sensors detect the presence of specific chemicals or classes of chemicals. Examples include oxygen sensors, also known as lambda sensors, ion-selective electrodes, pH glass electrodes, and redox electrodes.

Optical and radiation electromagnetic time-of-flight. Generate an electromagnetic impulse, broadcast it, and then measure the time a reflected pulse takes to return. Commonly known as - RADAR (Radio Detection And Ranging) are now accompanied by the analogous LIDAR (Light Detection And Ranging. See following line), all being electromagnetic waves. Acoustic sensors are a special case in that a pressure transducer is used to generate a compression wave in a fluid medium (air or water)

light time-of-flight. Used in modern surveying equipment, a short pulse of light is emitted and returned by a retro reflector. The return time of the pulse is proportional to the distance and is related to atmospheric density in a predictable way.

Ionizing radiation

Radiation sensors: Geiger counter, dosimeter, Scintillation counter, Neutron detection

Subatomic particle sensors: Particle detector, scintillator, Wire chamber, cloud chamber, bubble chamber

Non-ionising radiation

light sensors, or photo detectors, including semiconductor devices such as photocells, photodiodes, phototransistors, CCDs, and Image sensors; vacuum tube devices like photo-electric tubes, photomultiplier tubes; and mechanical instruments such as the Nichols radiometer. Infra-red sensor, especially used as occupancy sensor for lighting and environmental controls.

Proximity sensor- A type of distance sensor but less sophisticated. Only detects a specific proximity. May be optical - combination of a photocell and LED or laser. Applications in cell phones, paper detector in photocopiers, auto power standby/shutdown mode in notebooks and other devices. May employ a magnet and a Hall effect device.

scanning laser- A narrow beam of laser light is scanned over the scene by a mirror. A photocell sensor located at an offset responds when the beam is reflected from an object to the sensor, whence the distance is calculated by triangulation.

focus. A large aperture lens may be focused by a servo system. The distance to an in-focus scene element may be determined by the lens setting.

binocular. Two images gathered on a known baseline are brought into coincidence by a system of mirrors and prisms. The adjustment is used to determine distance. Used in some cameras (called range-finder cameras) and on a larger scale in early battleship range-finder

interferometer. Interference fringes between transmitted and reflected lightwaves produced by a coherent source such as a laser are counted and the distance is calculated. Capable of extremely high precision.

Scintillometers measure atmospheric optical disturbances.

Acoustic sound sensors: microphones, hydrophones, seismometers.

Acoustic: uses ultrasound time-of-flight echo return. Used in mid 20th century polaroid cameras and applied also to robotics. Even older systems like Fathometers (and fish finders) and other 'Tactical Active' Sonar (Sound Navigation And Ranging) systems in naval applications which mostly use audible sound frequencies.

Other types motion sensors: radar gun, speedometer, tachometer, odometer, occupancy sensor, turn coordinator

Orientation sensors: gyroscope, artificial horizon, ring laser gyroscope

distance sensor (non contacting) Several technologies can be applied to sense distance: magnetostriction

Non Initialized systems

Gray code strip or wheel- a number of photo detectors can sense a pattern, creating a binary number. The gray code is a mutated pattern that ensures that only one bit of information changes with each measured step, thus avoiding ambiguities.

Initialized systems

These require starting from a known distance and accumulate incremental changes in measurements.

Quadrature wheel- An disk-shaped optical mask is driven by a gear train. Two photocells detecting light passing through the mask can determine a partial revolution of the mask and the direction of that rotation.

whisker sensor- A type of touch sensor and proximity sensor.

Classification of measurement errors

A good sensor obeys the following rules:

the sensor should be sensitive to the measured property

the sensor should be insensitive to any other property

the sensor should not influence the measured property

In the ideal situation, the output signal of a sensor is exactly proportional to the value of the measured property. The gain is then defined as the ratio between output signal and measured property. For example, if a sensor measures temperature and has a voltage output, the gain is a constant with the unit [V/K].

If the sensor is not ideal, several types of deviations can be observed:

The gain may in practice differ from the value specified. This is called a gain error.

Since the range of the output signal is always limited, the output signal will eventually clip when the measured property exceeds the limits. The full scale range defines the outmost values of the measured property where the sensor errors are within the specified range.

If the output signal is not zero when the measured property is zero, the sensor has an offset or bias. This is defined as the output of the sensor at zero input.

If the gain is not constant, this is called nonlinearity. Usually this is defined by the amount the output differs from ideal behavior over the full range of the sensor, often noted as a percentage of the full range.

If the deviation is caused by a rapid change of the measured property over time, there is a dynamic error. Often, this behavior is described with a bode plot showing gain error and phase shift as function of the frequency of a periodic input signal.

If the output signal slowly changes independent of the measured property, this is defined as drift.

Long term drift usually indicates a slow degradation of sensor properties over a long period of time. Noise is a random deviation of the signal that varies in time.

Hysteresis is an error caused by the fact that the sensor not instantly follows the change of the property being measured, and therefore involves the history of the measured property.

If the sensor has a digital output, the signal is discrete and is essentially an approximation of the measured property. The approximation error is also called digitization error.

If the signal is monitored digitally, limitation of the sampling frequency also causes a dynamic error.

Sensor may to some extent be sensitive for other properties than the property being measured. For example, most sensors are influenced by the temperature of their environment.

All these deviations can be classified as systematic errors or random errors. Systematic errors can sometimes be compensated for by means of some kind of calibration strategy. Noise is a random error that can be reduced by signal processing, such as filtering, usually at the expense of the dynamic behaviour of the sensor.


The resolution of a sensor is the smallest change it can detect in the quantity that it is measuring. Often in a digital display, the least significant digit will fluctuate, indicating that changes of that magnitude are only just resolved. The resolution is related to the precision with which the measurement is made. For example, a scanning probe (a fine tip near a surface collects an electron tunneling current) can resolve atoms and molecules.


All living organisms contain biological sensors with functions similar to those of the mechanical devices described. Most of these are specialized cells that are sensitive to:

Light, motion, temperature, magnetic fields, gravity, humidity, vibration, pressure, electrical fields, sound, and other physical aspects of the external environment;

Physical aspects of the internal environment, such as stretch, motion of the organism, and position of appendages (proprioception);

an enormous array of environmental molecules, including toxins, nutrients, and pheromones;

Many aspects of the internal metabolic milieu, such as glucose level, oxygen level, or osmolality;

an equally varied range of internal signal molecules, such as hormones, neurotransmitters, and cytokines;

and even the differences between proteins of the organism itself and of the environment or alien creatures.

Artificial sensors that mimic biological sensors by using a biological sensitive component, are called biosensors.


Data acquisition

Data acquisition system

Data logger

Detection theory

Fully Automatic Time

Hydrogen microsensor

Lateral line


List of sensors

Machine olfaction

Receiver operating characteristic

Sensor network

About the Author:

Assistant professor in lord venkateswara engineering college.I am doing phd in sathyabama university, Tamil Nadu,India.

Article Source:

Sunday, April 12, 2009

The Workings of Magnetic Speed Sensor

How Does a Magnetic Speed Sensor Work?
By Rosa Telip Ten

For centuries speed sensors have been used to determine the speed of moving objects. In fact, the very first primitive speed sensors were lengths of rope with a knots tied in them that were tossed over the sides of moving ships to determine how many "knots" the ship was traveling at. However; the advent of the motorized wheeled carriage created the need for a more advanced mechanical speed sensor, such as the type that used a gear and a cable to run a speedometer on an automobile.

A Technological Need

As time and technology progressed however, the need for other types of accurate speed sensors developed. This in turn led to the development of what is often referred to as the magnetic speed sensor. So how do they work? How can a magnet detect and transmit the speed of a moving object?

The Hall Effect

It is not just the magnet in a magnetic speed sensor that is used to determine speed but an electrical current that surrounds the magnet as well. There is a certain electrical phenomena called the "Hall effect" that is used to determine the speed of an object with a magnet.

An Electrical Current

In short, when an electrical current is ran near a magnet and the magnet detects ferrous metal such as iron or steel the electrical current is effected. This electrical effect can then be transmitted by wires to a speed gauge where it can be displayed.

Gear Toothed Magnetic Sensor

Often a gear is used in conjunction with a magnetic speed sensor. As the gear spins or turns, each spline or tooth in it will be detected by the magnet as it passes and a corresponding electrical pulse is sent out. The faster the gear spins the faster the electrical pulses the sensor sends and thus a speed reading is made.

Written by Rosa Telipten. Now you can learn all you wanted to know about []Magnetic Speed Sensors and you will even find articles on Variable Reluctance Pickup.

Article Source: _


The AS5030 is a contactless magnetic rotary encoder for
accurate angular measurement over a full turn of 360°.
It is a system-on-chip, combining integrated Hall
elements, analog front end and digital signal processing
in a single device.
To measure the angle, only a simple two-pole magnet,
rotating over the center of the chip is required.
The absolute angle measurement provides instant
indication of the magnet’s angular position with a
resolution of 8 bit = 256 positions per revolution. This
digital data is available as a serial bit stream and as a
PWM signal.

AS5030 Datasheet

Friday, April 10, 2009

Hall Effect Sensors - What Makes Them Tick

Hall Effect Sensors - What Makes Them Tick
Rosa Telip Ten

Perhaps you have heard of magnetic speed sensors by now and are wondering just how they work? How in the heck can a magnet function to determine the speed of something? If it does, what on earth does the magnet focus on to work, because after all magnets respond to ferrous metals such as iron and steel.

Magnetic Speed Sensors

When someone is speaking about a magnetic speed sensor, what they really are referring to is a hall effect sensor. While they are commonly used in such systems as anti-lock braking systems in cars, they are now in common use in any number of high tech systems and machines that require the use of electronic transmission of speed or RPM data and information.

Say What!?

They get their name for the Hall effect which was discovered by a man by the name of Edwin Hall in 1879. In short, is refers to an electronic phenomena that is created on the opposite sides of an electronic conductor when an electronic current is flowing through it while a magnetic field is applied perpendicular to the current.

Still Need Ferrous Metal

While that is a mouthful to comprehend, in layman's terms it allows for mechanisms to be used to actually calculate the speed of something using electricity rather than a cable and gears. However; there has to be ferrous metal components of the system for the magnets in the sensors to focus on.

Counting Gear Teeth Real Fast

For instance, a gear tooth hall effect speed sensor, such as is in use in anti-lock braking systems uses a gear for the sensor to focus on and tracks the speed of the passing gear teeth to generate data that is sent to the main component that regulates the entire anti-lock braking system.

Article written by Rosa Telipten. Here you will get all the details you need on
Hall Effect Sensors and you can also find the best info on Hydraulic Motor Speed Sensor.
Article Source:

Thursday, April 9, 2009

Gear Tooth Hall Effect Speed Sensor

Everybody Knows What a Gear Tooth Hall Effect Speed Sensor is - So Why Don't You?
By Rosa Telip Ten

So what on earth is a gear tooth hall effect speed sensor anyway and do you really need to know? The fact is that if you drive a car with anti-lock brakes then you make use of them each and every time you drive your car. This is because they are the very latest technology in electronic speed sensors that are in use in automobiles today.

Magnetic Speed Sensors

Gear tooth hall effect speed sensors is a big mouthful of words to say, so these types of speed sensors are commonly referred to as magnetic speed sensors. They do in fact rely on the use of magnets in their function but it is the effect that the magnets have on electricity in sensor that powers their function.

Anti-Lock Braking Systems

Without electronic anti-lock braking sensors anti-lock braking systems would not be possible. It is the speed and frequency of the actual processes that transpires when anti lock braking systems are activated that requires the use of a high tech electronic sensor of this type.

The Focus on the Teeth in a Gear

Gear tooth hall effect sensors focus on and gage the number of gear teeth that pass by them to function. They use magnets to accomplish this and the information is passed on to a small central computer in the braking system that regulates the brakes in an anti lock braking system.

A Mouthful of Words

This process takes place up to twelve times every second and without this level of speed and accuracy anti-lock braking systems simply couldn't function correctly. So, the next time that you hear magnetic sensors being mentioned, you will now know that what the person is really talking about is gear tooth hall effect speed sensors.

Article by Rosa Telipten. Find the latest details on Gear Tooth Hall Effect Speed Sensor plus the best on []Magnetic Speed Sensors.

Article Source: _

Tuesday, April 7, 2009

Laser Distance Sensors Device

LDM 41 A / LDM 42 A
Laser Distance Sensors
- Measurement of distance and position
- Diameter measurement of rolls / coils
- Level measurement
- Position control
- Security application
- Observing and measurement for elevators
- Position measurement for cranes and conveyors

The LDM 41/42 A is a opto-electronic distance sensor for industrial
application, like distance and position measurement without use of
special reflectors. The target could be nearly any kind of natural
surface.The sensor works based on comparative phase
measurement. It emits modulated Laser light which is diffusely
reflected back from the target with a certain shift in phase to be
compared with a reference signal. From the amount of phase shift
a required distance can then be determined with millimeter accuracy.
A visible red Laser beam enables easier sighting. The LDM 42 A is
designed for fast measurement on white target

- millimetre precise measurement at various surfaces (LDM 42 A
only for white surface)
- long range reflector-less distance measurement, with additional
reflectors on the object over 100m with additional reflectors
mounted onto target
- high availability under in the high temperature area with high precision
- big supply voltage range 10 V until 30 V DC
- risk less use because of laser class 2
- simple alignment with a visible laser class
- bi-directional data-interface, switching and analogue output
- simple setup for parameter with a PC or laptop
- measured values are displayed in meters, decimetre, centimetre,
feet, inch etc. due to free scaling
- stable and simple to installing housing with protection IP 65
- Profibus DP via UNIGATE Gateway

LDM 301 A
Laser Distance Measurement Sensor


Equipment and performance features of the LDM 301 warrant
multiple possibilities of application in industrial environments

- Process monitoring in steel works and rolling mills
- Fill-level measurement
- Positioning of cranes, loading and handling equipment
- Measurement of points that cannot be accessed, for example, inside of cavities, tubes or containers
- Position monitoring of vehicles or ships

The new LDM 301 Laser distance sensor measures distance
and speed of natural targets without a reflector. A reflector can
be used for increasing the measuring range. The sensor needs
only a very short time to measure; it facilitates distance
measurement to or from moving objects. The laser pulse's
time-of-flight measurement principle which it uses is specifically
suitable where great distances have to be measured and for
applications in harsh industrial environments.

With the compact design shape, simple setup and configured with
standard interfacing facilities, the LDM 301 can easily be installed.
For interfacing an analogue output, 2 digital outputs and a serial
interface RS232 or RS422 are available.

Standard LDM 301 delivery includes integral heating, a status
display and a red Laser pointer. A modular setup allows for easy
complementation with accessories or special models as may be
required in particular applications

- Broad working range
- Great reach, also without reflectors
- Very short times to measure
- Laser class 1
- Programmable serial, digital and analogue outputs
-- Allows synchronization with external devices
- Compact design shape, IP67 protection
- Integrated red Pilot Laser, optionally telescope sign for alignment
- Easy to install and operate


Monday, April 6, 2009

Industrial Distance Sensor Device

Distance Sensor Model SR50

The SR50 is a rugged, acoustic distance sensor that is manufactured
by Campbell Scientific Canada. It measures the elapsed
time between emission and return of an ultrasonic pulse. This
measurement can be used to determine snow or water depth.
An air temperature measurement is required to correct for
variations of the speed of sound in air.

The SR50 was designed to meet the stringent requirements of
measuring depths and uses a multiple echo processing algorithm
to help ensure measurement reliability.
more pdf

Analog inductive distance sensor

184117 festo
Analog inductive distance sensor
The analogue inductive sensor contains an oscillator circuit, which
consists of a parallel resonant circuit with coil and capacitor as
well as an amplifier. The electromagnetic field is directed outwardly
by means of a ferrite shell core. If an electrically conductive material
is introduced into the active zone of the stray field, eddy currents are
induced into the material according to the laws of inductance, which
attenuate oscillation. Attenuation of the oscillator varies according to
the conductivity, permeability, dimensions and proximity of the
conductive object. The output signal, within a defined range, is
proportional to the distance between workpiece and sensor if the
workpiece material and dimensions remain unchanged.

more pdf

S80 Laser Distance Sensor

The S80 series, in a compact sturdy metal housing, offers an
innovative class 2 laser distance sensor with time-of-flight
measurement. This technology, based on the measurement of
the time between the emission and receipt of the laser light
pulses, ensures accurate distance detection.
The sensors function from 0.3 to 7m, within an adjustable range,
in positioning or detection applications, such as double-threshold
background suppression over long distances. All models have
two outputs, available in both the NPN and PNP models, that can
be set at different distances. While the measurement value is a
4-20mA analog output and RS485 serial interface; the latter can
be also used to set all the sensor parameters.
In addition, the S80 series offers the option to adjust the 4-20 mA
analog output. This feature allows the minimum and maximum values
of the operating distance to be set and linked to the minimum and
maximum current. A 4-digit display shows the distance, as well as
the parameters that can be set using the three buttons.

Common Applications

Sunday, April 5, 2009

InfraRed Distance Sensor Device

Optoelectronic Device
The GP2D12 is a distance measuring sensor with
integrated signal processing and analog voltage output.
• Analog output
• Effective Range: 10 to 80 cm
• LED pulse cycle duration: 32 ms
• Typical response time: 39 ms
• Typical start up delay: 44 ms
• Average current consumption: 33 mA
• Detection area diameter @ 80 cm: 6 cm

more pdf

Eowave InfraRed Distance Sensor

Eowave IR distance sensors are measuring sensor units,
composed of an integrated combination of PSD (position
sensitive detector) , IRED (infrared emitting diode) and signal
processing circuit. The variety of the reflectivity of the
object, the environmental temperature and the operating
duration are not influenced easily to the distance detection
because of adopting the triangulation method. This device
outputs the voltage corresponding to the detection
distance. So this sensor can also be used as a proximity sensor.
Distance measuring range :
Analog output type Continuous

Saturday, April 4, 2009

Ultrasonic Distance Sensor Device

PING Ultrasonic Distance Sensor

The Parallax PING))) ultrasonic distance sensor provides precise,
non-contact distance measurements from about 3 cm (1.2 inches)
to 3 meters (3.3 yards). It is very easy to connect to BASIC Stamp®
or Javelin Stamp microcontrollers, requiring only one I/O pin.
• Supply Voltage – 5 VDC
• Supply Current – 30 mA typ; 35 mA max
• Range – 3 cm to 3 m (1.2 in to 3.3 yrds)
• Input Trigger – positive TTL pulse, 2 uS min, 5 μs typ.
• Echo Pulse – positive TTL pulse, 115 uS to 18.5 ms
• Echo Hold-off – 750 μs from fall of Trigger pulse
• Burst Frequency – 40 kHz for 200 μs
• Burst Indicator LED shows sensor activity
• Delay before next measurement – 200 μs
• Size – 22 mm H x 46 mm W x 16 mm D (0.84 in x 1.8 in x 0.6 in)


Ultrasonic Distance Sensor

The Robotica Ultrasonic Distance Sensor measures the distance
or presence of a target object by sending a sound wave above
the range of hearing at the object and then measuring the time
it takes for the sound echo to return. By knowing the speed of
sound, the sensor can determine the distance of the object from
the transducer element

Friday, April 3, 2009

Ultrasonic Distance Sensor with the Microcontroller 2

Accurate Ultrasonic Distance Measurement Project


This paper introduces a different approach to
the measurement of the time-of-flight of ultrasonic signals.
Frequency variation monitoring and recording is used to
determine accurately the arrival time of the ultrasonic signal.
A high speed Digital Signal Processor (D.S.P.) is used for
both: transmission and direct measurement of the frequency
of the incoming signal in every single period and with an
accuracy of about 0.1%. The proposed configuration offers
small size and low cost solution to displacement
measurements with a remarkable performance in terms of
accuracy, range and measurement time.

The configuration of the proposed system is based on the
capabilities of accurate time measurement of modern microcontrollers.
The usual series of microcontrollers can not be
used in this application mainly because of their relatively
low frequency of operation (clock frequency) which affects
the accuracy of time measurement within one single period.
They can not offer the required fast and accurate frequency
measurement. A high performance system may therefore be
built only on a more powerful microcontroller. Larger
systems (personal computer type, etc) are avoided for
practical reasons; the overall measurement system should be
cost-effective and small sized.

More pdf

An Ultrasonic/Optical Pulse Sensor for
Precise Distance Measurements Project

- Develop an ultrasonic transit time distance sensor with an
optical sync signal
- Demonstrate a pulse cancellation technique for shaping
transmitted and received ultrasonic pulses.

System Block Diagram