Keithley 177 Instruction Manual page 37

Table 5-9. Ohms Source end Resistor Checks
Display
4
TP9"
5
INPUT HI to LO
6 INPUT HI to LO
7
1.9kl7 resistor.
8
Display
9
19kR resistor.
10 Display
11 190kC resistor.
12 Display
13 1900kD resistor.
14 Display
15 1OMD resistor
16 Display
..w'IY..Y" -.,.."...-..
Check chopper amplifier operation
per Table 5-7, steps 1 thru 10.
Select 2kD range. Short Input.
.OOOO *I digit.
-IV Approximately
Remove short end connect ammeter
from INPUT HI to LO. Source
current should be approximately
ImA, HI terminal negative.
Remove ammeter end measure open
circuit voltage. Voltage must be
-2 to -5v.
Apply to INPUT.
1.9000 * 12 digits.
Apply to INPUT. Select 20kD range.
19.000 -f 12 digits.
Apply to INPUT. Select 200kR range.
190.00 f 12 digits.
Apply to INPUT. Select 2000kR range.
1900.0 f 12 digits.
Apply to INPUT. Select 20MI2 range.
10.000 * 12 digits.
NOTE: Reference loading by the
ohms source does not affect D
readout since AID converter is
ratiometric.
I
*See Figure 5-l.
Table 5.10. Current Shunt Checks
Step Item/Component Required Condition
F
.." ..-...-
Inverted reference voltage
plus calibrated offset of
u107.
If incorrect, check R158 end
switching to INPUT HI end
chopper amplifier.
HI negative with respect to
LO. Display should be blink-
ing, indicating overrange.
Calibrated resistance.
Subtract test lead resistance
from reading. Checks
accuracy of R158 and feed-
beck loop to U107.
Calibrated resistance.
Source resistors: RI56 R154
(6975kDl. R157 (wiper).
Calibrated resistance.
Source resistors: R158, RI57
R156 (wiper), R154 l89.75kC.
8.975M).
Calibrated resistance.
Source resistors: R158, R157.
R156. RI55 fwiperl. R154, (all
except 6975MRl.
Calibrated resistance.
Source resistors: all R range
resistors. NOTE: To con-
veniently measure the resis-
tance of all D range resistors,
turn power off, set all
function switches out end
measure resistance INPUT HI
to LO.
.___
Remarks
L
Apply a known % scale
current end measure
voltage across shunt.
( Cl;;ping must occur et
5-11