Voltage Calibration - Keithley 236 Service Manual

SECTION 2
Calibration
29. On the Model 193A, select the Ohms function, 2002
range and disable ZERO.
30. Repeat step 3 to zero the Model 193A.
31. Measure and record the value of the 100Q resistor.
32. Set the Model 193A to DCV, the 2V range, and dis
able ZERO.
33, To cancel any offset, zero the Model 193A by short
ing its input(VOLTS HI to LO), and enabling ZERO.
34, Remove the short from the input of the Model 193A
and set the Model 263 to source 9.0000mA on the
2OmA range and enable OPERATE.
35, Record the voltage measurement from the Model
193A and caiculate the current.
I9mA 15
the characterized current for the 9mA range of
the Model 263. lt is used to calibrate the lOmA range
of the Model 236/237. Using a pendil, record the ca1
culated value of
IA
in Entry 5 of Table 23.
36. Place the Model 263 in standby.
37, In the test fixture, remove the 1002 resistor and in
stall the 1O2 resistor (R-18540).
38. On the Model 193A DMM, disable ZERO and select
the 200mVDC range.
39, While in standby, set the Mode1263 to +9.0000mA on
the 2OmA range.
40, Zero the Model 193A by shorting its input (VOLTS
HI to LO) and enabling ZERO.
41. Remove the short from the input of the Model 193A
and place the Model 263 in operate.
42, Record the voltage measurement from the Model
193A and then place the Model 263 in standby.
vb0
=
mV
43, Caiculate the actual resistance of the 1O2 resistor as
follows:
where; I is obtained from Table 23.
NOTE
To store calibration constants in nonvolatile
memory, place the CAL LOCK switch to the
unlocked "in" position (see paragraph 2.5).
With the switch in the locked "out" position,
calibration will be temporary. That
is,
the new
calibration constants will be lost when the in
strument is turned off,
2.6.2 Voltage Calibration
WARNING
The following procedure uses hazardous
voltages (1000V forthe Model 237) that could
cause injury or death, Exercise extreme cau
tion when encountering these lethal voltage
levels, Make sure to connect the Model 8006
Interlock Circuit to the Model 236/237
clx
! Calibrate common mode
Riooo
=
Rioo
iS
used to calibrate the lOOniA
range of the
Model 236/237.
vb00
=
v
vb 00
=
Riooo
mA
For voltage calibration, connect the Model 193A DMM to
the Model 236/237 via
the Model 8006 test fixture
as
shown in Figure 23. Jumper A is initially installed to
short the output of the Model 236/237 and the input of
the Model 193A,
Perform the following steps to calibrate the voltage
source and
measure ranges:
1. Set the Model 193A DMM to D volts and
autorange.
2. With the short (Jumper A) installed, zero the Model
193A by enabling ZERO.
3, Place the Model 236/237 in operate. The calibration
mode cannot be entered with the Model 236/237 in
standby.
4, Over the 1EEE488 bus, send the following command
to enter the calibration mode:
cox
! Enter calibration mode
Note: All other calibration commands (Cl through
C59) will be ignored unless the CO command is first
sent over the bus.
5, With the short still installed, send the following com
mand over the bus to perform common mode cali
bration:
Vb 00
RboQ
I9mA
24