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Introduction to the installation and testing methods of ultrasonic flowmeters

At present, two types of ultrasonic flowmeters are generally used, one is a Doppler ultrasonic flowmeter, and the other is a time difference ultrasonic flowmeter. The Doppler type uses the phase difference method to measure the flow rate, that is, the sound wave of a certain frequency moves in the fluid. Since the liquid itself has a moving speed, the frequency or phase of the ultrasonic wave between the two receivers (or the transmitter) occurs. Relative change, the liquid velocity can be obtained by measuring this relative change; the time difference type is to measure the flow velocity by using the time difference method, that is, the sound wave of a certain speed causes the propagation time between the two receivers (or the transmitter) due to the fluid flow. Change, by measuring this relative change, the fluid flow rate can be obtained. A time difference type ultrasonic flowmeter is currently used.

Ultrasonic flowmeters currently use three installation methods: W-type, V-type, and Z-type. The installation method is selected according to different pipe diameters and fluid characteristics. Usually, the W type is suitable for small pipe diameters (25 to 75 mm), the V type is suitable for medium pipe diameters (25 to 250 mm), and the Z type is suitable for large pipe diameters (250 mm or more). In short, in order to improve the accuracy and sensitivity of the measurement, the appropriate installation method is selected so that the measurement signal (ie, the difference) matches the secondary instrument.

In order to ensure the measurement accuracy of the instrument, the location of the site that meets certain conditions should be selected: usually the upstream 10D and the downstream 5D straight pipe sections are selected; the upstream 30D can not be equipped with pumping, valve and other disturbance devices.

1, zero flow inspection

When the pipeline liquid is stationary, and there is no strong magnetic field interference or strong vibration around, the meter shows zero. At this time, the zero point is automatically set to eliminate the zero drift. During operation, small signal removal is required, and the flow rate is usually less than the full flow. 5% of the automatic removal. At the same time, the zero point can also be adjusted through the menu.

2, instrument panel keyboard operation

Before starting the instrument, first set the parameters effectively, for example, using unit system, installation method, pipe diameter, pipe wall thickness, pipe material, pipe roughness, fluid type, two probe spacing, flow rate unit, minimum speed, maximum Speed, etc. Only when all parameters are entered correctly, the meter can correctly display the actual flow value.

3, the periodic calibration of the flow meter

In order to ensure the accuracy of the flowmeter, we carry out regular calibration. Usually we use a more accurate portable flowmeter for direct comparison and use the measured data to calculate: error = (measured value - standard value) / standard value, use The calculated relative error and correction coefficient make the measurement error satisfy the error of ±2%, which can meet the measurement requirements. The operation is simple and convenient, and the accuracy of the measurement can be effectively improved.

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