12-4
IM 760201-01E
12.4 NULL Feature
Procedure
Enabling the NULL Feature
1.
Press
SHIFT+MISC (NULL)
. The NULL feature is enabled and the NULL indicator
at the top of the screen lights.
Disabling the NULL Feature
2.
When the NULL feature is enabled, press
SHIFT+MISC (NULL)
. The NULL
indicator turns off, and the NULL feature is disabled.
Explanation
You can use the NULL feature to subtract the DC offset while an external sensor or
measurement cable is connected.
NULL Values
When the NULL feature is enabled, the NULL values are set to the most recently
measured Udc and Idc values (the voltage and current simple averages). If cases when
there are no previously measured Udc and Idc values, such as when the NULL feature is
turned on before any measurements have been made, Udc and Idc are set to zero.
Note
• The NULL feature is disabled when:
• The WT500 is turned on.
• A setup parameter file is loaded.
• The settings are initialized.
• You switch from direct input to external current sensor input during current measurement.
• If the NULL feature is enabled or disabled while the display is held, the NULL indicator
will light or turn off, but the held data will not be affected. Also, the NULL indicator will be
highlighted.
• DC values are held when the NULL feature is ON, but the actual NULL value is set with ±
10% of the range as the upper limit when the crest factor is set to 3.
The actual NULL value is set with ±20% of the range as the upper limit when the crest factor
is set to 6.
• When the range is changed, the NULL value upper limit will be determined by the new
range. The NULL value upper limit will also be adjusted when the range is decreased by the
auto range feature.
Measurement Functions Affected by the NULL Feature
Because the NULL values are subtracted from sampled data, all measurement functions
are affected by them.
