Calibrating the Model 133 via calibration coefficients
What is the process for performing a calibration in-house with my Model 133 (3-channel) signal conditioner?
The calibration process is a "Special" mode function and is initiated by pressing the < Select Function > push button while simultaneously pressing the < Left > and < Right > EDITS push buttons. Refer to page 17 of IM133.
The calibration process will utilize a fixed input voltage specified in the instruction manual, to the appropriate input. For the charge inputs, the voltage applied will be through a precision 1000pF capacitor. See Fig. 1.
- There are seven key main coefficients (K1-K7) *
- K1-K3 voltage input(Isotron input)
- K4 & K7(charge input)via, 1000pF capacitor
(1000pF capacitor- Meggitt Sensing Systems p/n 2947C)
The transfer function is: Q = EC
Q = Charge, in picocoulombs (pC)
E = Voltage, in volts (V)
C = Capacitance, in picofarads (pF)
- Gain Adjust- Fixed input voltage specified(at a frequency of 300Hz)
- K1-K3 (voltage applied to Isotron input), K4 & K7 (charge signal applied to charge input)
- Set required input signal for each coefficient;
- K1-30mV rms
- K2-300mV rms
- K3-3000 mV rms
- K4 & K7- 3000pC rms[ 3000mV rms into 1000pF capacitor = 3000pC rms]
- Adjust coefficients by < EDIT> button, i.e., adjusting calibration constant displayed on LED display until desired output is obtained.
- Verification of correct gain setting
- Return to normal operating mode
- Set gain within range of coefficient (Ex. For K2, 10 < gain < 100, set at 50 )
- Set input at appropriate level, utilizing an oscilloscope to ensure output is large enough, but not clipped
- Measure the output and calculate the actual gain ( Gain = output/input )
Results should be within 0.5% of setting
* Coefficients K5 & K6 are for A/D used in display. They are adjusted automatically with the correct input and initiation. The numerical display is just for reference.