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2. Remove the old calibration spring.
3. Install a new spring (when the center shaft of the potentiometer mechanism is turned
counterclockwise, the spring is wound tighter).
4. Replace the contact arm.
5. Loosen but do not remove three screws on underside.
6. Rotate the spring adjuster until slack is out of the spring and the contact arm lines up with
the contact strip. Tighten the screws.
7. Replace the shaft bearing retainer.
8. Calibrate the potentiometer.
Potentiometer Calibration
Depending on the frequency of its use, the potentiometer mechanism should be recalibrated
regularly and whenever the spring, contact arm, or resistor is adjusted or replaced. Higher
operating temperatures in the pressure chamber require more frequent recalibration of the
potentiometer.
Refer to the enclosed drawings of the calibration table assembly and Model 7322 assembly.
The step-by-step calibration procedure is as follows:
1. Rotate the pot mech calibration table out to the side of the instrument.
2. Install the potentiometer on the calibration table and insert the wedge into the open slot as
shown.
3. Wrap the steel cable around the potentiometer frame and over the pulley. Place the
hanger weight hook in the cord eye.
4. Install the wire-end clips to the potentiometer tabs. (Note the wire locations.)
5. Insert the plug on the end of the calibrator wires into the calibrator socket.
6. Turn on the master switch and place 400 grams of weight on the hanger.
7. The Bearden unit gauge should read 100 Bc. (100 Bearden Units is 1 volt). The contact
points of the spring should be oiled, the weights lifted and released, and the calibrator
lightly tapped to offset friction during the calibration. If the unit does not read 100 Bc,
manually adjust the pot mech calibration screw located on the face panel of the top
cabinet.
8. Refer to Drawing 07-0520, which is a typical calibration curve. The radius of the
potentiometer mechanism is 5.2 centimeters and is multiplied by the total weight on the
hanger to obtain gram centimeter torque.
9. Slurry consistency is expressed in Bearden units where 100 Bc is equivalent to the spring
deflection observed with 2080 gcm of torque (400 grams weight) using the weight-loaded
calibration device.
10. For further calibration details, refer to API Spec 10 booklet. This unit is supplied with
weights to accommodate the full range of tests per API specs.
Magnetic Drive
The magnetic drive should be flushed with clean water or oil whenever cement spills into the
cylinder or particles contaminate the drive. More frequent flushing of the drive is required
when high-temperature, high-pressure tests are run.
SECTION 3 – MAINTENANCE
3-3
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