1-11
1.9.4 Ohms verification
Ohms function accuracy is verified by connecting accurate
resistance standards to the Model 6517A and then verifying
that the readings on the display fall within the required ranges.
The following paragraphs discuss the required resistance
standards, how to compute voltage source values, and provide
detailed procedures for verifying accuracy of the ohms
function.
NOTE
Ohms specifications are dervied from amps
and voltage source specifications. Thus, it is
not necessary to verify ohms separately.
However, the following procedure is pro-
vided for those who wish to perform an
Artifact Standard Verification.
Required standard resistors
Resistance standards required include:
• Resistance calibrator (2M
Ω
-200M
Ω
ranges)
• Model 5156 Electrometer Calibration Standard
(2G
Ω
-200G
Ω
ranges)
• Characterized resistors (2T
Ω
-200T
Ω
ranges)
See Table 1-1 for detailed information on these recommended
standard resistors.
Calculating ohms reading limits
Ohms reading limits must be calculated from the actual stan-
dard resistance value and the appropriate Model 6517A spec-
ifications. For example, assume that the 2G
Ω
range is being
tested, and the specifications are:
• Model 6517A 2G
Ω
range accuracy: ±(0.225% of rdg + 1
count)
• 1G
Ω
resistor actual value: 1.025G
Ω
Calculated reading limits are as follows:
Reading limits = 1.025G
Ω
±[(1.025G
Ω
×
0.225%) + 10k
Ω
]
Reading limits = 1.025G
Ω
± 2.31625M
Ω
Reading limits = 1.02268G
Ω
to 1.02732G
Ω
NOTE
Before performing the ohms verification
procedures, calculate the reading limits for
each range, and enter the limits where indi-
cated in Table 1-9.
Instrument setup
Before performing the ohms verification procedures, you must
make certain that the instrument is properly configured as
follows. Failure to do so will result in erroneous or erratic
measurements.
Step 1: Select the auto voltage source mode
1. Press CONFIG and then R.
2. Select VSOURCE in the displayed menu, and then
press ENTER.
3. Select AUTO in the VSOURCE SETTING menu, and
then press ENTER.
4. Press EXIT to return to normal display.
Step 2: Select internal voltage source connections
1. Press CONFIG and then OPER.
2. Select METER-CONNECT in the CONFIGURE
V-SOURCE menu, and then press ENTER.
3. Select ON in the SOURCE-METER CONNECT
menu, and then press ENTER.
4. Press EXIT to return to normal display.
Step 3: Disable voltage source resistive limit
1. Press CONFIG and then OPER.
2. Select RESISTIVE-LIMIT in the displayed menu, and
then press ENTER.
3. Select OFF, and then press ENTER.
4. Press EXIT to return to normal display.
Step 4: Remove ground link
Remove the shorting link between COMMON and chassis
ground on the rear panel. Floating COMMON will elimi-
nate ground loops that might result in noise problems.
2M
Ω
-200M
Ω
range verification
1. Connect the Model 6517A to the resistance calibrator,
as shown in Figure 1-5.
2. Turn on the Model 6517A and the calibrator, and allow
a one-hour warm-up period before making
measurements.
3. Restore Model 6517A factory default conditions, as
explained in paragraph 1.7.
4. Select the ohms function by pressing R.
5. Select the Model 6517A 2M
Ω
range, and make sure the
filter is enabled.
6. Set the calibrator resistance to a nominal 1.9M
Ω
resis-
tance value.
7. Place the voltage source in operate.
8. Make sure zero check is disabled, and allow the reading
to settle. Verify that the displayed ohms reading is with-
in limits for the selected range listed in Table 1-9.
9. Repeat steps 5 through 8 for the 20M
Ω
and 200M
Ω
ranges.
10. Turn off the Model 6517A voltage source, then discon-
nect the resistance calibrator from the Model 6517A.