720A Operation and Maintenance Manual – Rev S – January 25, 2019
Page 25
13231 Rooster Springs Rd.,
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All calibration adjustment points are accessed by removing the
screws within the feet on the bottom of the unit, then lifting off
the top lid. Note that if your unit has an RS-232C interface you
will see two PC boards when you remove the top lid. All
calibration adjustments will be performed using trimmer
potentiometers (referred to as trim pots in this procedure) that
are on the larger PC board (also called the main board) below
the RS-232C board. All trim pots used within the calibration
procedure are accessible – meaning you will not need to
remove the RS-232C board.
Once the fifteen (15) warm up period has elapsed and you
have removed the unit’s top plate, you will then connect your
AMPTEC OP-300 lead set to the banana jack terminals on the
unit’s front panel. Alternatively, if your precision standards have
banana jack terminals, an AMPTEC OP-304 lead set may be
substituted. Then, select the range you would like to calibrate
(following the order outlined in the calibration adjustment in
section E-4.3). Next, you will connect your lead set to that
range’s corresponding resistance standard. Using a trimmer
potentiometer (also referred to as trim pots) adjustment tool,
you will then rotate the small screw-like component affixed to
the top of each trim pot that corresponds to each range (see
Figure 10)
. Once the unit displays the desired reading, you
have finished adjusting that particular range, and you may
move on to the next. Once all ranges have been calibrated, we
recommend verifying them all once more against your calibration standards before
closing your unit back up.
In the following subsections E-4.1 through E-4.3, you will find the locations of the trim
pots as well as more detailed information about the calibration adjustments necessary
to calibrate your 720A unit.
E-4.1 Equipment Required to Complete 720A Calibration Procedure
This section of the manual contains a list of the equipment you will need in order to
calibrate the 720A Digital Micro-Ohmmeter.
Precision Standard Resistors:
•
One 0.001 Ω resistance standard at ± 0.01% or better accuracy
•
One 0.01 Ω resistance standard at
± 0.01% or better accuracy
•
One 0.1 Ω resistance standard at ± 0.01% or better accuracy
•
One 1.0 Ω resistance standard at ± 0.005% or better accuracy
•
One 10.0 Ω resistance standard at ± 0. 005% or better accuracy
•
One 100.0 Ω resistance standard at ± 0.005%
or better accuracy
•
One 1.0 KΩ resistance standard at ± 0.005% or better accuracy
•
One 10.0 KΩ resistance standard at ± 0.005% or better accuracy
Figure 10
Trim Pot Adjustment Example
