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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.

  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)

    Figure 1

      • The transfer function is: Q = EC
      • Where:

        • Q = Charge, in picocoulombs (pC)
        • E = Voltage, in volts (V)
      • C = Capacitance, in picofarads (pF)
  2. 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.

    Figure 2

  3. 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.