LSI CDHT Series, User Manual

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14
4.0 Tester Calibration
4.0.1 Need for Calibration
The Larson hand tester is a precision measuring device that will require periodic calibration. The Tester should be
recalibrated on an annual basis or when force or length readings and or linearity appears suspect.
4.0.2 Calibration Options
Larson Systems offers two calibration options. Usually the most economical option is Factory Calibration. The
tester can be returned in original packaging to Larson Systems factory for calibration. Usual turnaround is less than
one week.
Larson Systems also offers calibration at your site for customers that prefer this convenience. Service is often
grouped with other customers in your area for economy.
Contact Larson Systems Service Calibration for further information (763-780-2131).
4.0.3 Required Calibration Equipment
Force Calibration
Calibration requires NIST traceable certified weights or NIST traceable certified load cells. Weights should be
available to test at ten equally spaced load points. Load cell displays should have resolution that equals or is
smaller than the tester resolution. Because of limited space on the platform for weights, the larger capacity testers
must be calibrated with a NIST traceable certified load cell.
Length Calibration
Calibration requires NIST traceable gage blocks, in increments to test at ten equally spaced lengths and indicator,
LSI PN 025-0000-202.
4.1 Force Calibration
4.1.1 Offset Adjustment
Pressing the Zero Force button will zero and tare load or drift up to maximum force of the tester.
4.1.2 Verifying Force Calibration
1. Starting with the tester off, press on to turn on the tester. Allow to remain on for 30 minutes before making any
adjustments.
2. Move the upper platform to its maximum up position.
3. Press force zero to obtain exactly zero on the display.
4. Apply loads in an ascending order in ten equal increments and record the results.
5. Reapply loads at least 3 times to establish repeatability.
6. Evaluate results. Error at each load increment must be less than the accuracy listed in section 1.3. Proceed to
section 4.1.3, Adjustment, if it is not possible to achieve the accuracy limits listed in section 1.3.
4.1.3 Force Adjustment
1. Turn tester off. Remove two screws holding the Force Display cover plate to the tester base and remove cover
assembly, allow cables to remain connected. Note! Be careful during this step and the following so that the PC
board does not touch the tester base.
2. Move the cover plate to a position where it is still connected to the tester but allows access to the two adjustable
potentiometers shown in Figure 13.
3. Press and hold mode then press on/clear to turn on the Force Display. Hold mode until Larson Systems has
been displayed. Display will show CAL in left hand side of display. Allow to remain on for 30 minutes before
making any adjustments.
4. Move the upper platform to its maximum Up position.
5. With no weight on platform, adjust the force zero potentiometer (P21) so that the display reads zero.
6. Press the force zero to obtain exactly zero on the display.
7. Apply approximately 85% full scale load to the tester and adjust the force full scale potentiometer (P1) to read
correctly.
8. Apply loads in an ascending order in ten equal increments and record the results.
9. Repeat three times to demonstrate repeatability.