Differential pressure transducers measure the difference between two lines of pressure.
While this can be emulated, or mimicked, by subtracting the output from two separate sensors, your accuracy reduces as you need to root sum square (RSS) the uncertainties from the independent sensors. In scenarios involving calibration, wind tunnel testing, or engine testing, even small errors can impact safety or regulatory compliance. Alternatively, a true differential reading applies pressure to opposite sides of the sensor, which allows you to work with a single accuracy statement. However, getting a highly accurate differential pressure measurement comes with its own challenges.
When you apply pressure to a typical piezoresistive sensor, this causes small deformations, or bends, in the sensor that causes small changes in resistance. This change in resistance affects the output signal, giving you the corresponding pressure measurement. The inherent characteristics of the sensor cause each sensor to deform differently with the same amount of pressure. Sensors can be characterized by accounting for these small variations in their signal output.
These unique deformations are also seen when using a differential sensor. However, since a differential sensor has both sides of the sensor being acted upon independently, this is an additional variable and source of uncertainty that needs to be addressed. As the static pressure varies, the differential output will vary as well. This is sometimes referred to as common mode effects, static line pressure effects, or simply line effects.
These line effects are found across all true differential sensors and may be indicated as an additional uncertainty specification in the datasheet. But how do they affect performance? Let's look at some examples:
In an ideal world, if you set both sides of a differential sensor to the exact same pressure, you would expect to see an output of 0, regardless of what pressure is actually being applied. However, this isn't the case. Here, the common mode pressure effects cause minor shifts in performance as a zero shift.
As you start to vary both the static and differential pressures independently, the static line effects start to include a span effect as well, further affecting the overall performance of the sensor. Take the example below: when running the sensor through its differential full scale (FS = 50 psi), the output changes depending on the static line pressure.
While the zero effect can be zeroed at the line pressure to remove the effect, in applications where line pressure isn’t constant, the static line effects will still be present.
When working with critical measurements, these effects can matter significantly. Our newest line of differential pressure transducers, the CPT8900 High Accuracy Differential Pressure Transducer, can compensate for this using common mode correction. This means that our new CPT8900 has been characterized to compensate for these effects across the entire range of the sensor.
Navigating differential pressure measurements requires accuracy and reliability — two qualities that the CPT8900 effectively provides. The experts at Mensor are here to assist you in learning more about this high-quality differential pressure sensor. Contact us today to gain more information about the CPT8900 and discover how it can assist with your daily operations.