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3-4
SECTION 3 – MAINTENANCE
The limit switch may require periodic adjustment. Use the following procedure to adjust the
limit switch:
Warning: Make sure the instrument power is off before performing this procedure.
1. Remove the cover plate from the limit switch assembly.
2. Bend the arm on the limit switch until the switch closes with an audible "click" as the
brass platen is manually lifted. The switch must close before the brass platen touches the
steel platen.
3. Manually operate the top limit switch and verify that the time delay relay inside the
power unit trips with an audible "click." The delay is set to approximately 20 seconds by
adjusting the knob at the top of the relay.
4. Replace the cover plate.
Calibration
Load Cell and Display and Controller Calibration
The display provides the excitation voltage for the load cell. The load cell calibration factor
(mV/V x the Excitation Voltage) is used as the scaling factor for the display.
The display and controller calibration is based on the calibration certificate provided with the
load cell and the excitation voltage (+10Vdc).
If the instrument must be recalibrated, an independent load cell must be loaded into the press
and used to validate the output of the load cell in the instrument.
1. To calibrate the load cell, use an independent measurement of the load, preferably
traceable to a primary standard. Create a load of approximately 10,000 to 50,000
pounds-force. Record the exact value.
2. Measure the excitation voltage from the display on terminals 1A and 1B at the back of
the display. Note this voltage.
3. Measure the output of the load cell corresponding to the known load at terminals V+ and
V-. The value will measure as millivolts (mV).
4. Divide the load cell output by the excitation voltage. This value is the new calibration
factor for the load cell, expressed in mV/V. Adjust the calibration factor by the ratio of
the measured load to 50,000 Lbf. The result will be the calibration factor at full scale
(50,000 Lbf).
Load
Cell
Output
(
mV
Exec
Voltage
(
V
)
)
mv
=
Cal
Factor
(
)
v
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