Keithley 2750, Service Manual

Page: 63 / 179

Model 2750 Multimeter/Switch System Service Manual Calibration 2-15
Mod
el 27
50 Cal
ibr
ation
NOTE DC calibration can be partially performed if desired. For example, to calibrate
only the 100¾ range, perform the DCU and 100¾ range steps, then save cali-
bration using :CAL:PROT:SAVE. Uncalibrated ranges will retain previous cali-
bration constants and can be verified as discussed in
Section 1 .
Short and open calibration
1. Connect the Model 8610 low-thermal short to the instrument INPUT and SENSE
terminals as shown in
Figure 2-1 . Make sure the INPUTS button is not pressed in
so that the front inputs are active. Wait at least three minutes before proceeding to
allow for thermal equilibrium.
NOTE Be sure to connect the low-thermal short properly to the HI, LO, and SENSE ter-
minals. Keep drafts away from low-thermal connections to avoid thermal drift,
which could affect calibration accuracy.
2. Send the following command:
:CAL:PROT:DC:STEP1
3. After the Model 2750 completes this step, remove the low-thermal short, and then
send this command:
:CAL:PROT:DC:STEP2
NOTE Be sure to minimize movement near front input terminals. Excessive movements
can cause capacitive coupling errors, which could affect calibration accuracy.
DC volts calibration
After the front panel short and open steps, do the following:
1. Connect the calibrator to the Model 2750 as shown in Figure 2-2 . Allow three min-
utes for thermal equilibrium.
NOTE Although 4-wire connections are shown, the sense leads are connected and dis-
connected at various points in this procedure by turning calibrator external
sense on or off as appropriate. If your calibrator does not have provisions for
turning external sense on and off, disconnect the sense leads when external
sensing is to be turned off, and connect the sense leads when external sensing is
to be turned on.
2. Perform the calibration steps summarized in Table 2-8 . For each step:
• Set the calibrator to the indicated voltage, and make sure the unit is in operate.
(Use the recommended voltage if possible.)
• Send the indicated programming command. (Change the voltage parameter if
you are using a different calibration voltage.)
• Wait until the Model 2750 completes each step before continuing.