For pressure compensation in Pitot tube flowmeters, should the accompanying pressure transmitter use gauge pressure or absolute pressure?

When selecting a pressure transmitter for pressure compensation in a Pitot tube flow meter, it is necessary to determine whether to choose a gauge pressure transmitter or a absolute pressure transmitter based on the application scenario and the specific requirements of the system. A gauge pressure transmitter measures the pressure relative to atmospheric pressure; in other words, it takes into account the effects of changes in atmospheric pressure on the measurement results. The measurement points located behind the fan are often subject to changes in the ambient atmospheric pressure, especially in open systems; a gauge pressure transmitter can provide an accurate reading relative to the current atmospheric pressure. An absolute pressure transmitter measures the pressure relative to a complete vacuum, that is, the total pressure exerted on an object, and it is not affected by changes in atmospheric pressure. In closed systems or applications that are not sensitive to changes in atmospheric pressure, absolute pressure transmitters provide the absolute value of pressure. Based on the information you provided, all flow meter measurement points are located behind the fan, with a pressure range of 14–70 kPa and a temperature below 80 degrees. In this case, if the system is closed and the changes in temperature and pressure are continuous and stable, it is feasible to use an absolute pressure transmitter, as the values it provides are not affected by changes in atmospheric pressure, thereby ensuring the accuracy of flow measurement. However, if the system is open, or if the atmospheric pressure in the environment may affect the pressure measurement results – for example, if the system is installed at a high altitude or if there are significant variations in atmospheric pressure – then a gauge pressure transmitter might be a better choice. Gauge pressure transmitters take into account changes in ambient pressure, making them more suitable for applications where variations in atmospheric pressure affect the measurement results. The final choice of transmitter type should also be determined through a comprehensive evaluation based on specific application requirements, the installation environment, and the overall design of the system. When making a decision, it is advisable to consult professional flow meter manufacturers or experienced engineers to select the type of pressure transmitter that is best suited for your application. .

There is no difference; when using absolute pressure for compensation in the control room, it needs to be converted to gauge pressure.

For this operating condition, you should choose a gauge pressure meter. The data used for temperature and pressure compensation is absolute pressure ； The measurement by a gauge pressure meter is not affected by the local environment and climate. Pressure transmitters are easier to maintain than gauge pressure transmitters, and they are also cheaper ； Under normal circumstances, the errors resulting from using voltage transformers for measurement are acceptable. The error resulting from using a pressure transducer to measure absolute pressure is approximately the ratio of the change in ambient pressure to the process pressure indicated by the absolute pressure ； When operating at low pressures, using a gauge pressure transmitter can reduce errors.

The main issue is that the gauge for absolute pressure is difficult to calibrate; when the gauge for gauge pressure shows a reading of 0, that’s it, but the gauge for absolute pressure is more complicated to work with, as a vacuum pump is required

For this operating condition, you should choose a gauge pressure meter. The data used for temperature and pressure compensation is absolute pressure ；