Editor's note: While the terminology in this post applies to both pressure sensors and pressure gauges (since they are built with the same transducer technology), the applications mentioned in this post are concerned with pressure sensors. You can find a similar post for pressure gauges here.
When selecting pressure transducers for your application, you will need to decide what pressure type your sensor will have. You must choose wisely as this will have a direct effect on the accuracy and durability of your sensor.
First, let’s do a quick review of the pressure types available for pressure transducers.
This type is used most often. When manufactured, the sensor’s reference point is set to ambient pressure. This way, it is unaffected by barometric changes because it is vented.
Just like gauge pressure, vacuum pressure is unaffected by barometric change because it is vented. The difference here is that vacuum pressure measures a negative pressure range.
Compound gauge pressure measures both negative and positive ranges. To put it simply, it is gauge pressure and vacuum pressure combined. And just like gauge and vacuum, it is vented so the zero point is set to ambient pressure.
Finally we get to a pressure type where barometric pressure changes will have an effect. Instead of being vented, the sensor is sealed at the factory. Therefore, the zero reference point is whatever the ambient pressure was at the factory when the sensor was sealed. In a moment we will explain the advantages of a sealed transducer and why and when you would want one.
This pressure type is also sealed and therefore affected by barometric changes. But instead of the zero reference point being whatever the ambient pressure was at the factory, the zero reference is set to full vacuum. This is accomplished by sucking all of the air out of the housing during production.
So why would you want to use sealed pressure transducers? The advantage here is better protection. In pressure measurement applications where there is a lot of moisture and dust it might be best to use a sealed transducer to protect the sensor’s electronics.
In regards to accuracy, at lower pressure ranges (below 500 PSI), it is best to use a transducer with a gauge pressure type. However, if you need that extra protection, you may be willing to sacrifice a few PSI units of accuracy for a longer lasting sensor.
Your pressure transducer's accuracy is affected because a sealed sensor doesn't adjust to barometric changes. You see, pressure is usually thought of as a relative thing. It's why your ears pop when you change elevations, and why deep-sea divers need to come back to the surface very slowly to reacclimatize. As barometric pressure changes, your sensor does not adjust, and will therefore have a seemingly unpredictable effect of a few PSI (either up or down) on your pressure readings.
For example, we have some customers that are using our PT-400 heavy duty pressure transducers on trucks that get pressure washed. The sensors only have a range of 200 PSI - so using gauge pressure would make the most sense for optimal accuracy. However, since the sensors are exposed to the pressure wash, our customer has opted for a sealed transducer. While the sensors are less accurate they last a lot longer.
At higher pressure ranges (over 1,000 PSI) we recommend that you just stick with a sealed transducer. At this point the barometric change will have such a minimal effect as to go unnoticed.
If you have any questions on what pressure type to use, or if you need help on a tough pressure measurement application, don’t hesitate to contact us.
