Pressure sensors: The top 10 things not to do
Elden Tolman, design engineer of the Automation Products Group and his team have heard and seen just about everything when it comes to level sensors and pressure transducers. They’ve detailed the top 10 things not to do with a pressure sensor. The order of this list was determined based on two factors: frequency of the mistake, and the seriousness of the offense.
10: Calibration without reference
If you must recalibrate a sensor yourself, then be certain you have an accurate reference with which to calibrate. Otherwise, you will end up with an inaccurate sensor.
9: Ignoring enclosure protection ratings
If the application is one that experiences high moisture or humidity, then use a sensor that is rated for such environments. Using an indoor rated sensor in an outdoor environment is a poor choice, and will most likely result in moisture damage.
If you are measuring ranges that are well below your sensor’s specified range, you are under-ranging. If the application range is below 50% of the sensor’s range, you are sacrificing resolution and accuracy. Accuracy is rated based on the full scale, so 0.25% of full scale is a larger error band for high pressure rated sensors.
7: Incorrect wiring
Always verify that a sensor has been wired properly, according to specification, before applying power. 24 Vdc is not the same as 120 Vac!
6: Improper handling of the diaphragm
The diaphragm is the sensing element of the pressure transducer. It needs to be protected from damage. Rough handling of the sensor often results in non-conforming sensors. This is more frequent with flush mount sensors when the diaphragm is more exposed.
5: Using as a tool
It is important to remember that you are working with instrumentation, not tools. They are not designed to be used as anchor points, hitches, or levers, and you must be careful about how you tighten them.
If you are measuring ranges well above the specified range of your sensor, then you are over-ranging. While it is true that over-pressure specs are intentionally conservative, it is a poor practice to rely upon them long term. Over-pressure ratings are defined with the understanding that it will be a rare occurrence. These ratings are not intended for standard operating ranges and will degrade the life of the sensor.
3: Improper ground
Multiple ground locations should be avoided. They can cause ground loops that will affect sensor performance, and can even compromise both wire shielding and surge protection. Electrolysis damage is a common result, particularly with submersible sensors.
2: Chemical incompatibility
If the wetted surface is not chemically compatible with the media being measured, it is only a matter of time before the sensor will fail. Even seemingly benign fluids and gasses can cause problems. For example, water is not compatible with all materials.
1: Wrong process connection
The threads of the sensor fitting or process connection need to match up and be properly rated for the pressure that will be applied. Not doing so will likely result in either damage to the process connection or in creating an unsafe situation. This is especially true in high pressure situations.