Characteristics to be noted in the use and selection of differential pressure sensors

Characteristics to be noted in the use and selection of differential pressure sensors

Differential pressure sensors are generally used in test benches, wind tunnels, leak detection systems, and other applications. This article mainly explains six characteristics and precautions when selecting sensors for differential pressure and critical pressure applications.

Directional effect
Incorrect installation, vibration, and even system maintenance can cause changes in the orientation of differential pressure sensor equipment, which is known as directional effect. For other types of sensing technologies, directional effects have always been a problem. Even correctly installed sensors can have edge gravity effects, as rotating the sensor 180 degrees will change from positive gravity to negative gravity, resulting in a force change of 2G. In this case, the sensor cannot distinguish between the force applied by gravity and the force applied through the pressure port. Therefore, the sensor will combine the gravity weighted effect with the port pressure and emit incorrect signals. For sensors filled with silicone oil or other isolation media, the directional effect during sensor rotation will be more pronounced. The weight of the diaphragm and the weight of the filling liquid of these sensors will affect the differential pressure sensor. Similarly, sensors cannot measure the true pressure and will emit incorrect values due to changes in orientation.

Vibrate
The low-frequency vibration of nearby motors or fans can also affect the correct positioning of sensors. For example, the liquid in the oil filled sensor may pick up low-frequency vibrations and apply inertial loads to the diaphragm, which may be mistaken for process pressure changes. To avoid this vibration effect, the end user needs to install the sensor in a quiet area at the far end. Similarly, if the reference port is connected to the atmosphere, it needs to be connected to an area without vibration noise and wind. For wind tunnels, due to the installation of pitot tubes, both pressure ports can be connected to remotely installed sensors through hoses or semi hoses, thereby preventing air disturbance noise or mechanical vibration from being transmitted to the sensors.

Overvoltage protection
Overpressure protection and backpressure protection of differential pressure sensors have always been a concern for leakage system manufacturers, who seek smaller leakage rates in differential pressure and high static pressure applications. Leak detection manufacturers always hope to measure increasingly lower leak rates. Due to the proportional relationship between leakage rate and differential pressure, these manufacturers hope to measure increasingly smaller differential pressures. To achieve this goal, the static testing pressure should be increased to a higher level.

Pipeline pressure impact
In addition to overpressure, changes in pipeline pressure also need to be considered, especially in leak detection applications with high static pipeline pressure. Pipeline pressure is the pressure applied to the sensor port. However, some changes in static pipeline pressure may cause slight stress deformation of the sensor profile. These stresses will also alter the calibration response of the sensor, affecting its zero point and range. The design adopted by the new generation of sensors can significantly reduce the strain of sensing elements caused by static pressure. Searching for sensors with rated low voltage effects,

Response time
The response time of differential pressure sensors is a major factor for pressure control and wind tunnel applications. The response time of a sensor (the time interval between the pressure applied and the output signal generated by the sensor) is determined by the technology and electronic components used in the sensing element of the sensor. Diaphragm using capacitive sensing technology usually responds quickly. They detect and measure pressure by sensing voltage changes across the capacitor, with one electrode of the capacitor being a diaphragm that can reflect slight changes in applied pressure. The resulting capacitance changes will be detected by the electronic components of the sensor, which will output a proportional high-level signal after linearization, thermal compensation, and modulation.

Response application
The requirement for fast response time of differential pressure sensors depends on the application. For example, in wind tunnel applications that measure dynamic airflow velocity changes, the signal output of the sensor varies with wind speed, thus requiring a fast response time. For most test bench, leak detection, and wind tunnel applications, a response time of 10-80 millimeters is usually acceptable. For traditional processing and monitoring applications where response time is not very important, the response time is usually a few seconds instead of milliseconds. When designing a system, it is important to understand the response time requirements of pressure sensors, as the response time of pressure sensors is not always as fast as possible. If the sensor response speed is too fast, sometimes the fast sensor will respond to brief unfiltered and unwanted system noise or turbulent pressure fluctuations. In this case, filtering the output signal can attenuate these unwanted interferences.