SECTION 5
MAINTENANCE
5.1 INTRODUCTION
This section contains information necessary to maintain the
Model 220. Calibration adjustment, troubleshooting, fuse
replacement, line voltage selection, fan filter cleaning and all
information pertinent to maintenance is provided.
5.2 CALIBRATION
Calibration should be performed yearly (every 12 months.1 or
whenever performance verification (see Section 3) indicates
that the Model 220 is out of specification. If any step in the
calibration procedure cannot be performed properly, refer to
paragraph 5.4 for troubleshooting information or contact
your Keithley representative or the factory.
WARNING
All service information is intended for
qualified electronic maintenance person-
nel only.
5.2.1 Recommended Test Equipment
Recommended test equipment for calibration is listed in
Table 5-1. Alternate test equipment may be used. However,
the accuracy of the alternate test equipment must at least
be equal to the specifications in Table 5-I.
5.2.2 Environmental Conditions
Calibration should be performed under laboratory condi-
tions having an ambient temperature of 23°C f I°C and a
relative humidity of less than 50%.
5.2.3 Warm-Up
The Model 220 must be turned on and allowed one hour for
warm-up. If the instrument has been subjected to extremes
of temperature, allow sufficient time for internal tempera-
tures to reach normal operating conditions. Typically, it
takes one hour to stabilize a unit that is IO°C 118°F) out of
the specified temperature range.
5.2.4 Calibration Fixtures
In order to meet the specifications of the Model 220, the
IOMDand 1GIl resistors used to calibrate the Model 220
must be enclosed in a guarded fixture. The guarded fixture
must be constructed. The following items are necessary for
proper construction of the calibration fixture:
I. 1OMR Resistor, Keithley Part Number R-305-10M
2. IGQ Resistor, Keithley Part Number R-289-1G
3. Two enclosed chassis boxes, one to be placed inside the
other and insulated from each other.
4. One Triax Connector, Keithley Part Number CS-181
5. One Banana Jack, Keithley Part Number BJ-II
The test fixture shown in Figure 5-2 is to be used to calibrate
the 1fiA and lOOnA ranges. A duplicate test fixture must be
constructed with the 1GTi resistor in order to calibrate the
1OnA and InA ranges.
Figure 5-l. Calibration Setup
Table 5-l Recommended Test Equipment
Item
A
:
D
E
F
:
I
Description
DMM
Resistor”
Resistor*
Resistor*
Resistor*
Resistor*
Resistor*
Teraohmeter
Calibration Fixture
Specification
f0.00596 to lo&
100 k.l%
loon f .l%
IkD f .l%
1OOkfl + .02%
IOMD f .25%
1GD ~2%
NOTE*
.
Before placing the resistors in the test configurations, measure them and note the value. Zero
the Model 192 before measuring the 100, lOOR, 1kD and the 1OOkR resistors with the Model
192. Measure the 1OMD and 1GD resistors with the Guildline 9520. These values will be used
later in the calibration procedure.
Mfr.
Keithley
Keithley
Keithlev
Keithley
Keithley
Keithlev
Keithlev
Guildline
Model
192
R-185-10
R-308-1003
R-315-1 k
R-182s100k
R-305~10M
R-289-I G
9520
5-1
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