Keithley 486 Instruction Manual page 163

SECTION 7
Maintenance
73.6
IEEE-488 Bus Calibration
The following procedures will demonstrate how to use
the 'Z" command and "V" col~u~ll d over the IEEE-488
bus to calibrate the Model 486/487. For simplicity, all
other operations of the Model 486/487 and calibration
equipment will be controlled manually from the front
panel.
The following simple program in HP BASIC 4.0 can be
used to send calibration
comman ds to the Model
486/487. When this program is run, it will prompt you to
enter the calibration command string. After sending the
conunand,theModel486/487willsend areadingbackto
the computer that will be displayed. Also, this program
uses the U3 status word
to
acquire and display the cali-
bration value that was sent over the bus. For this pro-
gram, the primary IEEE-488 address of the Model
486/487 is set to 22.
HP BASIC 4.0 PROGRAM
COMMENTS
10 REMOTE722
!
Send
remote
enable.
20 PRINT "INTER CALIBRA- ! Prompt for command.
TION COMMAND"
30 LINPUTA$
! Input COInman d string
from keyboard.
40 OUTPUT 722; A$
! Send co mmand siring
to 486/487.
50 ENTER 722; B$
! Get a reading
from
486/487.
60 l'RINTB$
! Display reading on
computer CRT.
70 OUTFVT 722; 'TJ3x" ! Progrml for u3 status
word.
80 EiWER722; C$
! Get calibration value
from 486/487.
90 PRINTC$ ! Display calibration
value.
100 GOT0 20
110 END
! Loop back.
In practice, it is recommended that calibration be fully
automated. A well designed computer Program can
con-
trol all instrument operations (Model 486/487, Model
263, and Model 197 J1973).
Picoammeter Calibration
In
general,
current calibration consists of applying a
source value of +19O,OOO counts to each range and then
sending the appropriate calibration command. Table 7-3
lists the required calibration current and calibration
com-
mand for each range.
NOTE
After a calibration command is sent over the
bus, front panel controls are locked out. To
perforxi a front panel operation make sure
you first press the LOCAL key.
Perform the following steps to calibrate the current
ranges of the Model 486/487:
1. Make sure CAL LOCK is pressed "IN" and return
the Model 486/487 to factory default conditions as
follows:
A. Press and release MENU until the following
message is displayed:
DEFAULTS OK
B. Use the rotary knob to display the following
message:
DEFAULTS FACTORY
C. Press MENU. The instrument will return to fac-
tory default conditions.
2. Connect the Model 263 current source to the Model
486/487 as shown in Figure 7-2. Configure the
Model 263 for V/R AMPS and make sure that
GUARD is disabled and the ground link is installed.
3. On the Model 486/487, disable autorange (Press
SHIlT and then AUTO RANGE). Place the Model
486/487 on the 2nA range.
4. Set the Model 263 to the 2nA range and apply
1.9OOOOnA to the Model 486/487.
5. Gnthe Model 486/487, disable zero check to meas-
ure the calibration current source.
6. Send the following command over the JEEE-488 bus:
L3,1.9E-9X'
While the instrument is performing calibration, the
following message will be displayed:
cALrSk4l-E
WORKING
After the selected range is calibrated, the instrument
will return to the normal measurement display state.
7. On the Model 486/487, enable zero check.
8. Place the Model 486/487 on the 2OnA range, set the
Model 263 to source 19.OOODnA on the 2OnA range,