Introducing REZCOMP™ Sensor Resonance Compensation
REZCOMP™ technology extends the frequency response of pressure, microphone and accelerometer sensor measurements.
Precision Filters in collaboration with Kulite Semiconductor Products developed the patent pending REZCOMP technology to extend the frequency response of pressure sensors, accelerometers, microphones and other resonant sensors in real-time with no need for post-processing. Resonances from recessed mounted pressure sensors, the protective screen over the cavity containing the sensor element or the seismic mass of an accelerometer are effectively compensated by REZCOMP. Using data provided by the sensor manufacturer, the user enters in the GUI the frequency and Q characteristics of the resonance to compensate the transducer for a flat sensor amplitude response and a linear phase response. The application of REZCOMP technology typically extends useable sensor bandwidth by 200-300%1 or more.
Compensation for Three Categories of Transducer Resonances
Sensor Packaging Resonance
For measurement of unsteady pressure, aerodynamically driven resonances associated with the sensor packaging can produce large gain and phase errors in the frequency range of interest (10 Hz to 20 kHz). When a piezo-resistive MEMS pressure sensor is packaged in the transducer housing, a screen covering is used to protect the semiconductor-sensing element from foreign particle impingement. The cavity volume behind the screen produces aerodynamically driven resonances on the order of 20 kHz to 100 kHz which overlap and limit the usable sensor frequency response. The resonance causes unwanted amplification and phase shift errors in the measurement and if not accounted for, can exceed the maximum signal swing of the amplifier and severely distort the measurement.
Recessed Mounted Pressure Measurements
For applications where the sensor cannot be mounted flush with the flow field due to temperature and other constraints, the sensor is often recessed at the end of a tube. The tube produces an organ-pipe resonance that amplifies the pressure signal by 20dB or more depending on the length of the tube and other properties. This resonance limits the useful measurement bandwidth to about 20% of the first resonance or about 1 kHz for a 1" tube.
Pressure transducer recessed length, L, from flow field
Pressure Sensor Taps
Accelerometer Mechanical Resonance
PE, PR and IEPE Accelerometers are mechanical structures that have a well-known under-damped seismic resonance of the sensing mass. The mounted response of the accelerometer is limited by the frequency response of the accelerometer, which is often modeled as a simplified damped spring mass second order system. A generally accepted rule is to limit the useable response of the accelerometer to only 20% of the sensor resonance where the response will have approximately 5% of amplitude peaking and 5 degrees of phase shift. Such a constraint under-utilizes the native sensor bandwidth that may contain important information about the device under test.
REZCOMP flattens all three of the above resonant responses and compensates for phase as well in order to extend the frequency response of the sensor. REZCOMP compensation is based on user entry of sensor quality factor Q and resonance Fr. The complementary transfer function is programmed to flatten the sensor frequency response and linearize the sensor phase response. Vendors such as Kulite™ provide Q and Fr data specific to each sensor. For even more accurate results, the sensitivity of Q and Fr to temperature may be accounted for by entering the operating temperature of the sensor1.
The resonant response caused by the protective screen of a pressure sensor or microphone is eliminated using REZCOMP technology.
When applied to an accelerometer with Q of 10 extends useable 5% bandwidth to the resonant frequency of the sensor.
As the block diagram below illustrates, programmable pre-filter gain is first applied to the input signal in order to preserve signal-to-noise ratio of the in-band sensor signal while allowing for headroom for out-of-band signals. Next, the sensor frequency response correction is applied to compensate for the resonance of the sensor. The programmable filter is then applied to the signal to eliminate out band energy and to prevent aliasing. The signal is then further amplified using post-filter gain to ensure the full use of the A/D dynamic range after compensation of the resonance characteristics.
It is possible to correct for undesired resonance by post-processing test data however post-processing data after digitization can result in poor signal-to-noise ratios since the A/D input must accommodate both the in-band signal of interest and the sensor resonance. Allocating amplifier headroom for the sensor resonance results in reduced amplification of the small in-band signal above the self-noise of the signal conditioner and A/D. This results in sub-optimal signal-to-noise ratios regardless of the resolution of the A/D. The REZCOMP correction approach provides superior real-time performance by maximizing signal-to-noise ratios.
1 Hurst, A. M., Carter, S., Firth, D., Szary, A., and VanDeWeert, J., 2015, "Real-Time, Advanced Electrical Filtering for Pressure Transducer Frequency Response Correction," ASME 2015 Gas Turbo Expo, ASME, Montreal, Canada, pp. 1-13.
Signal Conditioners with REZCOMP
- 2-channels per system
- Optimized for Conditioning Kulite pressure sensors and microphone products
- Bipolar Constant Volgage Excitation with Remote Sense
- Multi-channel solution optimized for piezo-resistive pressure, accelerometer and other bridge type sensors
- 4-channels/ card,
- Excitation: Constant Voltage with Remote Sense or Balanced Constant Current™
- Multi-channel solution optimized for PE and IEPE sensors
- 4-channels/ card,
- Dual mode: IEPE or Charge