4.11 Maintaining Measurement Precision (Self-Calibration)
57
4
To maintain measurement precision, the instrument self-calibrates every ten minutes to compensate
for internal circuit offset voltage and gain drift. This function cannot be disabled.
During self-calibration, the subsequent measurement is delayed for about 6PLC + 10 ms (PLC =
Power Line Cycles) for internal circuit compensation.
Self-Calibration Timing
Within 130 ms at 50 Hz, or 110 ms at 60 Hz
• When the timing of self-calibration overlaps with a measurement, self-calibration is postponed until the end
of measurement.
• When a trigger signal is applied during self-calibration, the start of the triggered measurement is postponed
until self-calibration is finished.
• Self-calibration executes automatically after changing comparator or measurement speed settings.
• During self-calibration, measurement current and the Contact Improver current are inhibited.
This function automatically compensates for offset voltage resulting from thermal emf or internal
instrument bias. (OVC: Offset Voltage Compensation)
See: "Appendix 2 Effect of Thermal emf" (p. A2)
The following value is known to be a true resistance value from R
P
(>0), the value measured with
current flowing in the positive direction, and R
N
(<0), the value measured with current flowing in the
negative direction.
Offset voltage compensation is automatically enabled in the following conditions, and cannot be modified or
disabled:
• When a range from 100 m to 10 is selected.
• When low-power resistance measurement is enabled (LOW POWER: ON).
When the test object is inductive, some delay (DELAY2) is required (p. 42) to allow adequate current flow
before starting measurement.
4.11 Maintaining Measurement Precision
(Self-Calibration)
4.12 Compensating for Thermal EMF Offset
(Offset Voltage Compensation - OVC)
R
p
R
N
–
2
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