Positions of the temperature and pressure points for temperature and pressure compensation in flow measurement
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When measuring flow rate using the temperature and pressure compensation method, the pipeline is generally reduced in diameter due to the flow meter. In such cases, should the pressure measurement points be taken on the pipeline after the diameter reduction or before it? Additionally, can the temperature and pressure measurement locations be placed within the required straight sections before and after the flow meter? This post was last edited by marry on 2009-4-1 19:22.]
To avoid affecting the fluid profile, the temperature is generally set outside the straight pipe section following the flow meter, right?
Temperature and pressure should be parameters upstream of the flow meter and should be located outside the straight pipe section of the flow meter.
The temperature point should have little impact; the pressure gauge is located on the positive pressure side, that is, in front of the flow meter
Neither temperature nor pressure should be measured at the straight section of the flow meter, as this will affect the accuracy of flow measurement. The exact location for measurement depends on the specific conditions on site; it doesn’t matter whether the thermometer is placed before or after the flow meter, while it’s better to measure pressure on the positive pressure side of the throttling device.
The temperature and pressure measurement points must be located on the pipe before the reduction in diameter, not on the pipe after the reduction. Because after throttling, the pressure and temperature may change, and the pipes themselves present resistance, this can easily lead to errors in compensation.
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It should be taken from the pipe after necking
If the pressure measurement point is located on the straight pipe section before the flow meter, it should have no impact on flow measurement. There must be a change in pipeline pressure before and after the diameter reduction, right? Taking the pressure measurement at the pipeline after the diameter reduction should provide a more accurate reflection of the pressure at the flow meter.
The pressure should be before the throttling device, while the temperature should be after it (5D).
Discussion based on the installation specifications for Yokogawa vortex flowmeters: 1. The basic principles of temperature and pressure compensation; the temperature and pressure values used for compensation should ideally be those of the medium flowing through the flowmeter. Therefore, in principle, it is better for the thermometers and pressure gauges to be as close as possible to the flowmeter, as being too far away renders compensation ineffective. 2. Whether there are reductions in diameter, valves, or elbows before or after the flow meter, as long as the temperature or pressure measurement points are not too far from the flow meter, the effect of the throttling element on the aforementioned measurement results is minimal, or even negligible. As long as the sensing element affects the flow rate measured by the flow meter, it’s better to keep a distance without hesitation. 3. Adequate insulation of the pipes, selection of appropriate flow meters, proper installation, maintenance and management are all far more important than the choice of temperature and pressure monitoring points. 4. The Yokogawa vortex street installation guidelines recommend that the pressure measurement point be located 2–7D behind the flow meter, while the temperature measurement point should be 1–2D behind the pressure measurement point; this clearly illustrates the aforementioned basic principle: the pressure loss associated with any flow meter is limited, so there is no need to worry excessively about whether the temperature and pressure measurement points are placed in front of or behind the flow meter ； Relatively speaking, pressure sensing points cause less interference with flow measurement than thermometer sensing points; therefore, temperature measurement is performed after pressure measurement. Obviously, the temperature and pressure measurement points can be located in the straight section behind the flow meter; in my opinion, as long as it does not affect flow measurement, these points should preferably be placed in that straight section behind the flow meter, rather than in the sections with varying diameters that come after it.