Pressure transmitters are designed to operate in the most difficult and challenging conditions. Despite design efforts, we still see “failed” and misapplied product – however, a lot of these “failures” can be prevented via proper specification, installation, and maintenance practices. At this year’s Emerson Global Users Exchange in Nashville, I had the opportunity to co-present the Pressure Transmitter Best Practices training course, where we covered various tips for extending the installed life of a pressure transmitter. Let’s take a look at a few of these best practices below:
1. Specification – Material Selection
Transmitter performance is certainly important to consider, but beyond this perhaps obvious consideration, selecting the proper materials of construction for your transmitter can also play a big role in its lifespan. Proper material selection serves two main roles: it ensures process compatibility and protects against environmental effects. The most important material selection to get right is the isolating diaphragm material; this is the part of the transmitter that comes into contact with the process, so if the isolating diaphragm becomes compromised, the pressure measurement will also. Especially tricky applications to look out for are those with hydrogen or environmental corrosion that may require more specialized materials of construction for the diaphragm. Similarly, enclosure material selection is also important. The enclosure protects the electronics and wiring by resisting environmental corrosion and maintaining ingress protection, allowing the transmitter to function reliably.
If you are looking for support with material selection, check out this free online Material Selection Guide or reach out to your local sales representative or Emerson technical specialist.
2. Installation – Impulse Piping
Proper mounting position of the transmitter can not only protect your transmitter from potential damage, but also allow for a more reliable process reading. The state of the process fluid (gas vs liquid) will determine the best transmitter mounting orientation. For gas applications, it is recommended to mount the transmitter above the pipe to keep liquid out of the impulse piping, and the impulse piping should be at a slope to prevent the formation of a meniscus in the piping which can impede proper measurement. For liquid applications, it is recommended to mount the transmitter below the pipe, also with impulse piping at a slope, to keep gas out of the piping. It is also advised to keep impulse piping to a minimum, as impulse piping can introduce its own issues: the potential for leaks, plugging, temperature effects…all of which can impact the integrity of the pressure measurement. Today, some smart transmitters have features such as Advanced Diagnostics that can notify you if the pressure measurement has potentially been compromised, such as by a plugged or frozen impulse line, for additional measurement insight.
3. Maintenance - Calibration
Calibrations are performed to ensure the device accuracy is within spec after days, months, or years of operation, with the frequency often depending on site or sometimes government requirements. However, if not done properly, it is actually possible to de-rate the performance of the transmitter via calibration! Calibration equipment should be at least four times as accurate as the pressure sensor to avoid degrading sensor performance. If it is believed that a calibration has caused additional inaccuracies, you can perform a Factory Calibration Recall which will restore the transmitter’s calibration settings to how it was shipped originally from the factory.
Because it can be very easy to inadvertently de-rate the transmitter’s performance with a calibration or trim, it is recommended to instead perform a “verification” when possible. Similar to a calibration, a verification includes confirming that the transmitter is operating within acceptable accuracy requirements, but does not include a sensor adjustment as long as the transmitter is within spec.
These are just a few of the many considerations to keep in mind when choosing and using a pressure transmitter. Proper selection, installation, and maintenance of your pressure transmitter can help ensure you’re getting the longest life and best possible performance out of your instrument. Interested in attending a similar training with more of this information? Check out Emerson’s variety of course offerings at Emerson.com/RosemountTrainingServices.