I want to use Endevco® model 8510B piezoresistive pressure transducers to measure the profile of a small, fast-acting gas valve, such as those used to control air or nitrogen within HVAC applications. The valve pressure profile changes very quickly, almost like a step change. Transducer rise time response is not specified on your product datasheet. Can this product measure fast rise times? How can I accurately calculate rise time response?
Yes, the model 8510B (and the entire Endevco® 8500 pressure transducer series) can measure extremely rapid rise time pressure pulses. Meggitt does not specify rise time response on the product datasheet. Instead, we specify sensor resonance frequency. This allows the user to apply general dynamic measurement "rules-of-thumb" to calculate rise time response, given that the pressure transducer itself can be approximated as a single degree-of-freedom mass-spring mechanical system with practically no damping.
To further illustrate, the "period" of the sensor is simply the reciprocal of the resonance frequency specification:
In order to remain within the linear region of frequency response, it is recommended to use no more bandwidth than 1/5 of the total sensor resonance frequency. This bandwidth is the "flat" region of sensor frequency response.
Thus, the above equation becomes:
Now, from Fourier analysis, it is well known that rapid rise time pulses contain high-frequency content. In order to avoid exposing the sensor to these high frequencies (to prevent distortion and signal overshoot), it is recommended that the transducer's period be 1⁄4 to 1⁄2 of the expected rise time, or:
By solving for T and substituting into the previous equation, we arrive at:
So, given a sensor resonance frequency specification, we can now accurately calculate pressure transducer rise time response.
For example, the Endevco® model 8510B-500 has a specified resonance frequency of 500 kHz. Using the above equation, the rise time response would come out to:
In addition to the HVAC related application example highlighted here, the Endevco® model 8510B series may also be used to effectively support the pressure monitoring requirements of wind tunnels, blast and ballistics, hydraulics systems, wave studies, chemical reactors, and automotive airbag and transmission safety testing.