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

OmniInstruments.net

---------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: http://www.articlesbase.com/gps-articles/ultrasonic-flow-meter-some-basic-principles-381312.html

DYNAMETERS FIXED TRANSIT-TIME ULTRASONIC FLOWMETER
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.

more

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.
Features
• 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)
more

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

more

Ultrasonic Distance Sensor with the Microcontroller 2

Accurate Ultrasonic Distance Measurement Project

Abstract
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 SYSTEM
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

Goals
- 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

more pdf

Ultrasonic Distance Sensor with the Microcontroller 1

Ultrasonic Distance Sensor Implemented
with the Microcontroller Project
Linear measurement is a problem that a lot of
applications in the industrial and consumer market
segment have to contend with. Ultrasonic technology is
one of the solutions used by the industry. However, an
optimized balance between cost and features are a must
for almost all target applications. The ultrasonic distance
measurer (UDM) is used mainly when a non-contact
measurer is required. This is the type of solution this
document explains using a simple robot toy
implementation.

Description
The UDM is a demo that shows capability and performance
of the MC9RS08KA2 and the ultrasonic sensor to build a
distance measurer. Figure 2 shows the basic building block of
this project.

The firmware generates a 40 kHz burst signal. After the 10 cycle
burst is completed, a variable that measures the distance is
activated. This variable measures the time sound takes to rebound
and is used for distance calculation.

The burst signal goes to the ultrasonic transmitter (US Tx) and is
transmitted as ultrasound through the air Figure 2. When the wave
is reflected off an object, this wave is captured by the ultrasonic
receiver (US Rx.) This received signal is amplified because it
attenuates as it travels. Afterwards, the signal goes back to the
microcontroller unit (MCU), filters it and calculates the distance.
A 40 kHz interrupt is generated by the timer in the MCU. To
perform this, the keyboard interrupt (KBI) is enabled and detects
the external signal. Every time the MCU is interrupted the counter
is increased by three. And the variable used as a counter is
decreased by one for the entrances to the modulus timer module
(MTIM) interrupt service routine (ISR). When this variable is bigger
than eight the ECHO signal is activated. The distance variable is then
set to 0. Refer to Figure 3 for timing diagram. For detailed information
about the firmware see Figure 3.

More pdf


Distance Sensing Project
devices for wireless distance and position determination
usefull as gesture controllers for robotic musical instruments
Since the early seventies we did build sonar devices to control our
self made analog electronic music synthesizers. In those years,
simple to use transducers were not readily available on the
electronic component market and so, we had to make our own,
based on designs used for underwater hydrophones. (Quarz crystals,
inductive devices, self made condensor microphones etc...). Although
the focus of our research later on became doppler based sonar
and radar movement detection and gesture analysis, we always had
quite a few pulsed sonar devices at hand. The easiest and cheapest
ones to build nowadays make use of the commonly available 40kHz
transducers. Two approaches are possible: either one uses a single
transducer as an emitter for a periodic burst of sinewaves and that
then is switched to microphone mode and connected to the input of a
voltage controlled amp (preferably a logamp, compensating for the
square law decay of amplitude with distance). The time between the
start of the burst and the reception of the first echo is a linear function
of the straight distance from the tranducer to the reflective object or
body.

More pdf