Choosing the right pressure transducer for your application depends on a variety of factors.
Here are 10 important things to consider when selecting pressure transducers:
Gauge, absolute or differential
Digital (query response or continuous)
Ambient and media temperature
Pressure/reference fittings and adapters
There is not a hierarchy of need implied in this list. One attribute or a subset of these may be more or less important to you. Your application will determine which one is most important. For simplicity and with a nod to David Letterman, we'll start at 10 and go down.
Reason: The size of the transducer you choose will have to fit where it is intended to be used. This may not be a problem for an industrial plant application or manufacturing environment, but could be a crucial selection factor for an original equipment manufacturer (OEM) that has limited space within an enclosure.
Action: Measure the space where the transducer will be used.
9. Pressure / Reference Fittings and Adapters
Reason: The pressure and reference fitting that connects the transducer to the process must be compatible.
Action: Check availability of adapter fittings that will facilitate ease of connection within the existing design.
8. Enclosure Rating
Reason: The enclosure for the transducer must have a rating that will prevent exposure to harmful external conditions, including ingress of liquids, humidity, dust or gasses.
Action: Check the Ingress Protection Rating (IP) of the transducer to verify its compatibility with the expected external contaminants.
7. Body Material
Reason: The body material of the transducer must be suitable for the environment in which it is deployed.
Action: Verify compatibility with any corrosive or weathering elements that may exist in the application environment.
6. Wetted Material
Reason: The pressure medium may be a corrosive liquid or gas, so the wetted material of the transducer must be compatible.
Action: Check the transducer specification for the material(s) that will be in contact with the application medium. Determine if there are suitable isolation components within the transducer that protects the sensing element. If necessary, consider external media isolation components like diaphragm seals or separators.
5. Ambient and Media Temperature
Reason: The media temperature and the ambient temperature where the transducer will be used should be within the limits prescribed for the transducer. High and low temperatures outside the transducer limits can damage the transducer and affect the accuracy.
Action: Check the temperature specification of the transducer and the proposed environmental conditions and medium temperature for the proposed application.
4. Signal Output
Reason: The signal output of the transducer must match your existing infrastructure or the communication protocols designed into your application. These outputs could be an analog electrical signal like 4-20 mA, a voltage signal, or a digital signal that is sent on demand or via continuous output. The reading output rate or readings per second should also be compatible with the application to ensure that all data is captured, including intermittent or transient spikes.
Action: Check the communication protocol of the prospective transducer to make sure you have the means to communicate and the rate of transmission is acceptable.
3. Pressure Range
Reason: The pressure range is one of the more important features of the transducer. The minimum and maximum range that will be encountered in the application must be encompassed by the transducer's range. Because the accuracy is often a function of the full scale range, a range just high enough should be considered to achieve the best accuracy.
Action: Check the transducer specification. It will either have a list of set ranges or a customizable range that can be chosen between a minimum and maximum boundary. Range availability will be different for each pressure types (see below).
2. Pressure Type
Reason: The pressure type is defined by the reference pressure of the measurement. Absolute pressure is measured relative to absolute zero pressure, gauge pressure is measured relative to atmospheric pressure, and differential pressure is the difference between one arbitrary pressure and another.
Action: Make sure what kind of pressure you need to measure and check the transducer specification to see if it is available.
Reason: The accuracy may be the most important characteristic. It tells you how close the pressure measurement is to the actual pressure. Depending on the application this may be of utmost importance, or the reading from the transmitter may only be used as a ballpark figure. Either way, it gives some degree of certainty in the measurement being transmitted.
Action: Check the transducer specification. It will give a value for accuracy as a function of the transducer's pressure range. Care should be taken in the interpretation of this value as different manufacturers report accuracy in many different ways.
These are the top ten things that we think are important in choosing the right transmitter. Leave a comment below if you can think of some more.
- Analog Output from a Digital Pressure Transducer
- Serial Communication Interface: Differences Between RS-232, RS-485 and RS-422
- How to Zero Absolute Pressure Transducers and Sensors
- Long-term Stability in Silicon Pressure Transducers
- Calibration Terms: Differences in Sensor, Transducer and Transmitter
- Comparing Different Types of Analog Pressure Transducers