74X Series
Calibration Manual
34
The other functions are also calibrated by following the step-by-step instructions on the
display.
Frequency Source: When you calibrate the [Frequency Source] function, it requests
that you measure the frequency and voltage output. This signal is an approximate 50%
duty cycle, positive square wave, and the amplitude needs to be measured in pk volts, so
multiply the DMM reading by 2. The DMM must be a true-RMS type.
mA Measure: When you calibrate the [mA Measure] function, the display requests 0.0
mA input. This does not equate to a short between mA high and low. Instead, set the
source device to source 0.0 mA, which is in effect the same as an open circuit.
TC Measure: For [TC Measure] calibration, refer to the Thermocouple Measure part of
the Verification Procedure for the correct techniques. [TC Measure] should be calibrated
using ITS-90 standards.
Ohms Source: Always configure the DMM in a 4-wire configuration.
Adjustment of Potentiometers
There are three potentiometers on the Main PCA: R61, R77, and R82. These are factory
adjusted to tune out common mode error. Normally these should never need re-
adjustment. If after a repair you need to repeat this adjustment, proceed as follows.
1. Carefully gain access to the Main PCA, and carefully power on the UUT.
2. Set the calibrator to the [
DC Voltage Measure] function.
3. Short the front panel
V MEAS high and low jacks together.
4. Apply 10V at 60 Hz between the
V MEAS high jack and TP12 on the Main PCB.
5. Adjust R82 for a minimum output measured between TP24 and TP12. This value
must be less than 3 mV rms.
6. Remove the jumper, then set the UUT to the [
DC Current Measure] function.
7. Apply 10V at 60 Hz between
mA/Ω/RTD MEAS low jack (common) and TP12.
8. Adjust R61 for a minimum output measured between TP17 and TP12. This value
must be less than 12 mV rms.
9. Set the UUT to the [
TC Measure] function, any type.
10. Short the TC jack "+" and "-" terminals.
11. Apply 10V at 60 Hz between the TC jacks and TP12.
12. Adjust R77 for a minimum output measured between TP40 and TP12. This value
must be less than 3 mV rms.
13. Remove the jumper.
To Next Page
Loading...
