CALIBRATION PROCEDURES
53
The calculation of the displayed leakage current will use 1000
Ω
for R in the
calculation of V/R=I where I is the leakage current displayed and V is voltage across
the measuring device (MD). The probe should be selected to P
H
-P
L
and the MD
selected to F. When an external frequency generator is applied to the probe inputs then
the current display will be equal to Voltage generator/1000. The readings can then be
correlated to verify the voltmeter bandwidth. Since the voltage is being applied directly
across the MD voltmeter amplifier inputs it is not necessary to actually install a 1K
Ω
resistor to the external MD:F inputs. However, to complete the circuit a jumper should
be applied between the two red terminals V and I of the external MD:F inputs.
14.2.4
Meter Auto Zero
Press the SETUP key, the program will advance to the Meter Auto Zero calibration.
The display will show:
Meter Auto Zero
TEST to start
Make sure that Probe HI and LO are shorted and that the DUT power connection have
been disconnected. There should not be any DUT input voltage during the Auto Zero
calibration.
Press TEST and wait for the 7611 to check the zero of each range. The first line shows
the range. Two numbers appear on the second line. The number on the left (NU=XX)
is the auto-null DAC setting that minimizes the RMS to DC converter output offset.
The number on the right (OS=XX) is the residual offset after the auto-null. This offset
is subtracted in software to make the reading zero when there is no input. No user
adjustable parameters are necessary. The screens will be displayed as follows as the
auto zero is executed.
Auto zero . . .
takes
∼
90 sec.
Range 0 null . . .
NU = XX , OS = XX
Range 1 null . . .
NU = XX , OS = XX
Range 2 null . . .
NU = XX , OS = XX
Range 3 null . . .
NU = XX , OS = XX
Range 4 null . . .
NU = XX , OS = XX
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