IET Labs RS-925D, Руководство пользователя и обслуживания

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9
RS-925D
9 Maintenance
5.3.2 General Considerations
Before starting the calibration procedure, you need
to consider the following:
• Calibration environment should be 23°C and
less than 50% relative humidity.
• Test instruments should be sufficiently more
accurate than the RS-925D unit, and/or the
uncertainty of the measurement instrumenta-
tion has to be considered in the calibration
Test Uncertainty Ratio (TUR).
• The testing equipment and the RS-925D unit
should stabilize at laboratory conditions for
at least 24 hours.
• Kelvin type 4-wire test leads should be
used to obtain accurate low resistance
measurements.
• Steps should be taken to minimize thermal
emf effects, such as using a meter with “True
Ohm” capacity.
• Accepted metrology practices should be
followed.
5.3.3 Required Equipment
Many combinations of standards, transfer standards,
meters, and bridges may be used to calibrate this in-
strument. The following are some possible choices:
• Resistance Standards or Transfer Standards
for 1
Ω
, 10
Ω
, 100
Ω
, 1 k
Ω
, 10 k
Ω
, 100 k
Ω
,
1 M Ω , and 10 M Ω per step, calibrated to
±10 ppm. IET options include the follow -
ing models:
• HATS-LR
• HATS-Y
• SRL Series
The 1 Ω , and 10 Ω transfer standards are
optional, and are only used to take advantage,
if desired, of the trimmability of these two
decades
• Precision resistance measurement bridge
or multimeter, with a transfer accuracy
of ±l ppm. Options include:
• Guildline Model 9975
• Measurements International Model
6000A
• ESI model 242, 242A, 242C, or
242D
• A high-precision, high-stability digi-
tal multimeter (e.g. Fluke 8508A)
along with a set of resistance stan-
dards for ratio mode.
5.3.4 Calibration procedure
To calibrate the RS-925D unit, proceed as follows:
1. Set up the calibration equipment in the re-
sistance measurement mode and exercise the
switches 10 times in each direction.
2. Allow the switches to cool for 15 minutes.
3. Confirm the minimum resistance of the unit.
Allow a confidence band for the uncer -
tainty of the measuring instrument and
setup.
4. Determine the allowable upper and lower
limits for each resistance setting of each
decade based on the specified accuracy and
the confidence band.
For the RS-925D series, the limits for
any resistance “R” are:
[R±(20 x 10
-6
R + 0.0005Ω)].
5. Confirm that the resistances fall within these
limits.
6. If any resistances fall outside these limits,
the associated switch assembly may require
service or replacement.