Resistor R13 - Fluke 5220A Instruction Manual

DVM Reading ( mV dc)
0.87 to 0.174
0.175 to 0.261
0.262 to 0.348
0.349 to 0.435
0.436 to 0.522
0.523 to 0.609
0.610 to 0.696
0.697 to 0.783

4-40. Resistor R13

Resistor R13 is associated with the DC Accuracy Adjustment procedure and the setting
of the GAIN ADJ potentiometer R3. Use the following procedure to select the proper
replacement for R13:
1. Disconnect the 5220A from line power.
2. Remove the top and large inner covers from the unit.
3. Connect the precision shunt (.01 ohm) to the enabled output terminals of the 5220A.
4. Connect the DVM to the sense terminals on the precision shunt; observe polarity. Set
the DVM to the 100 mV range and zero the display +/-.001 mV.
5. Connect the output of the dc voltage calibrator to the VOLTAGE INPUT terminals
on the 5220A; positive to red, negative to black.
6. Adjust R3 on the A5 Preamplifier to its full cw limit.
7. Install a shorting wire across R13 on the A5 Preamplifier PCB Assembly.
8. Connect the 5220A to line power and set the POWER switch to ON.
9. Set the calibrator for an output of +10.0000 V dc.
10. Set the 5220A to the operate mode.
11. Determine the actual value of the precision shunt (calibrated value) and subtract it
from .01 ohms. Multiply this difference by 10,000 and record the result.
12. Record the displayed DVM reading in mV and add the result of step 11 from the
reading. Use this corrected DVM reading in conjunction with Table 4-5, to select the
value of R13.
For example:
Given: Shunt Value = .0100123
DVM Reading = 101.041 mV dc
Corrected DVM Reading = 101.041 + 10000 (.01-.010012)
Corrected DVM Reading = 100.918 mV dc
R13 = 698 ohms (see Table 4-5.)
13. Set the POWER switch on the 5220A to OFF and replace R13 on the A5 Preamplifier
PCB with the selected value.
14. Perform the Calibration Adjustment procedures.
Table 4-4. Replacement Resistors for R11 and R12
Selected Value for R11/R12
1.00 k
2.00 k
3.01 k
4.02 k
4.99 k
6.04 k
6.98 k
8.06 k
Replacement of Selected Components
Fluke Part Number
168229
235226
312645
235325
168252
285189
261685
347229
Maintenance
4
4-17