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CALIBRATION
6
6-11
6-10. Basic Calibration Procedure
The basic calibration procedure consists of the following four parts. These parts must be
performed in the order shown.
1. Initial 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).
Normally, it is recommended that the entire calibration procedure be performed.
However, under some circumstances the earlier parts may be omitted. For example, if
installing the True RMS AC option, it may be necessary only to perform Offset and Gain
Calibration for the ac functions, followed by High-Frequency AC Calibration. But if the
A/D Calibration is performed, it must be followed by a complete Offset and Gain
Calibration for all functions and then by High-Frequency AC Calibration.
Some of the calibration calculations are complex and take the 8842A some time to
execute. For example, when you store the zero input during the Offset and Gain
Calibration for the VDC function, it takes around 22 seconds before the next prompt
appears. (The 8842A automatically uses this input to calibrate the offset for all ranges.)
While the 8842A is executing a calibration step, it ignores all of the front panel buttons
and postpones execution of all remote commands.
6-11. INITIAL PROCEDURE
Always begin the calibration procedure as follows:
1. Allow the 8842A to stabilize in an environment with ambient temperature of 18°C to
28°C and relative humidity less than 75%.
2. Turn the 8842A on and allow it to warm up for at least 1 hour.
3. Enable the calibration mode by pressing the CAL ENABLE switch with a small
screw-driver or other suitable instrument. (The CAL ENABLE switch is located on
the right side of the display and is normally covered by a calibration seal.)
When the calibration mode is enabled, the CAL annunciator lights up, and the 8842A
displays the first prompt for the A/D Calibration procedure (Figure 6-2). To exit the
calibration mode, press the CAL ENABLE switch again.
f6-02.wmf
Figure 6-2. First A/D Calibration Prompt
In the calibration mode, the front panel controls assume the functions described in Figure
6-3. Some of these functions are advanced features and are not required for the basic
calibration procedure. The display blanks briefly when a button is pressed.