What Are The Main Considerations When Selecting A Differential Pressure Sensor
Important considerations when selecting a differential pressure sensor are presented. These include the highest level of pressure and the range of differential pressures that the sensor can take. First of all, this particular device, which may also be a differential pressure transmitter, has the task of measuring the difference between two or more pressures. The value is often utilized as input for a process feedback system to make sure that the process is running within the desired range of parameters. An important consideration when choosing this kind of device is to avoid the confusion about the pressure ratings. Because the measured pressure is the difference between two values, this is relatively small compared to gauge pressure or absolute pressure. Therefore, there is the danger of exposing the product to too much pressure if the expected differential pressure is utilized as basis for determining the ratings of the differential pressure sensor to be purchased.
There is also the possibility that the pressure that would be exerted on the sensing diaphragm of the differential pressure sensor will not be even throughout the length of this device. The uneven distribution of the stress can result in a modification of the analog output signal if the mechanical configuration of the sensor is not designed to handle this type of stress. The skewed distribution of the pressure is likely to offset the sensing diaphragm so that it would become off-center from its previous location. The uneven distribution of forces on the sensing diaphragm can actually affect the whole sensor because this particular part is connected to several other components.
Some of the sensors that could be affected by uneven pressure are those that have thin and fragile isolation membranes at both sides of the sensing diaphragm. The potential problem is that the volume of the oil that is found inside the transducer can increase or decrease in size depending on the temperature. To avoid this problem, the design of the isolation membranes could be adjusted in such a way that the thermal expansion or contraction of the oil will not affect the sensing diaphragm too much. Meanwhile, another way to avoid the above problem is to have dry transducers, such as the Keller pressure sensors. Because the temperature has less effect on solids, these sensors are more stable although they are not completely free from the changes caused by temperature.
There are other innovative ways to avoid the above-mentioned errors in the differential pressure sensor. Two absolute pressure sensors may be used for those situations when the differential pressure is much bigger than the common values. Some manufacturers have placed mechanical stops for the diaphragms to prevent uneven loading of different ends of the device. For those situations when precision is of utmost importance, you may have to carefully examine the product data sheet regarding thermal zero errors. Sometimes, the accuracy is only provided for ambient temperature. Therefore, you will have to look elsewhere in the data sheet for the accuracy for other temperatures. And when there is substantial variation in the line pressure, it is advisable to use a DP transmitter with an absolute pressure sensor that compensates for shifts in the line pressure.