5700A/5720A Series II
Operators Manual
4-58
4-63. Sensing
External sensing is required only when the voltage drop in the cables is significant. The
following data determines the significance of the voltage drop in the cables:
•
The input impedance of the 8840A is ≥ 10,000 MΩ for ranges up to 20V, and 10 MΩ
for the 200V and 1000V ranges.
•
The total resistance of the Model 5440A-7002 Low-Thermal Cables is 30 mΩ.
Cable voltage drop is insignificant because this is a high-impedance meter, so in this case
internal sensing is appropriate.
External sensing should be used for resistance calibration in the two-wire function,
however, so the calibrator’s two-wire compensation circuitry can sense at the meter
terminals.
4-64. Basic Calibration Procedure
The basic calibration procedure consists of the following four parts. These parts must be
performed in the order given.
1.
Calibration setup procedure
2.
A/D calibration
3.
Offset and gain calibration for each function and range
4.
High-frequency ac calibration (True RMS AC option only)
4-65. Calibration Setup Procedure
1. Allow the 8840A to stabilize in an environment with ambient temperature of 18 to
28ºC and relative humidity less than 75%.
2.
Turn the 8840A on, and allow it to warm up for at least one hour.
3.
Turn the calibrator on, and allow it to warm up for at least 30 minutes.
4.
Execute dc zeros calibration. Do this by pressing the following sequence of softkeys:
“Setup Menus”
→ “Cal” →“Zero”
5.
Press P twice to get out of the calibration menu.
6.
Enable 8840A calibration mode by pressing the 8840A CAL ENABLE switch with a
small screwdriver or other suitable instrument. (The CAL ENABLE switch is located
on the lower right side of the display and is normally covered by a calibration seal.)
7.
Verify that the calibrator’s STANDBY annunciator is lit and connect the calibrator to
the 8840A using Low Thermal Cables as Figure 4-13A shows.
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