How to Calibrate the MNM MS720-15K 15,000 lb x 2 lb Crane Scale
- pete8781
- Jul 30
- 3 min read
Call (832) 290-3120 or email mnmscales@yahoo.com for calibration support, indicator identification and help selecting an appropriate reference load for this 15,000 lb system.
Calibrating the MNM MS720-15K means calibrating the complete installed measurement chain, not merely the metal S-beam. The load cell, mounting hardware, cable, connector, indicator electronics, gravity setting and test fixture all influence the final displayed force. MNM sells this unit as calibrated and ready to use, but recalibration or verification is appropriate after sensor replacement, significant fixture changes, shipping damage, connector repair, unexplained drift or when your quality procedure requires periodic checks.
Before calibration: establish a trustworthy mechanical zero
Remove all force from the S-type load cell. Check that the eye bolts and adapters are aligned with the load axis and that nothing is rubbing, bottoming out or preloading the cell. Inspect the cable for cuts, crushed sections and loose connector hardware. Power the indicator and allow the electronics to stabilize. Record the unloaded reading before pressing zero. If the reading wanders significantly while the sensor is truly unloaded, solve the mechanical or electrical problem first; a zero key can hide an offset but cannot fix an unstable system.
Zero calibration
The correct service-menu sequence depends on the exact indicator supplied with the MS720-15K. The product page describes the indicator’s functions but does not publish a model-specific calibration menu, so do not copy an OP-901 or LP7515 button sequence unless the shipped indicator is positively identified as that model. Once the correct manual is confirmed, perform the indicator’s zero or dead-load calibration with the fixture in its normal unloaded state. If the fixture itself is part of the tare structure, keep the same hardware installed during zero and span calibration.
Span calibration with a known force
Apply a traceable known force through the same load path used in normal operation. For a 15,000 lb system, use an appropriate calibrated test machine, reference load cell, certified proving system or controlled weight arrangement that is safe for the magnitude involved. Do not improvise a high-force calibration by suspending enormous uncontrolled deadweights. Enter the known force value using the verified indicator procedure, allow the reading to settle and store the span point. A higher calibration point generally provides better full-range sensitivity than a tiny fraction of capacity, but the correct load depends on the reference equipment available and the range you actually use.
Multi-point verification
After zero and span are stored, verify several increasing and decreasing loads. A useful check might include a low point, a midrange point and a higher point within the approved test setup. Record indicated force, reference force and error at each point. Repeat at least one point to judge repeatability. If upward and downward readings differ materially, investigate fixture friction, hysteresis, joint movement and side loading. A perfect single span point cannot compensate for a poor mechanical load path.
Peak Hold verification
Peak Hold should be checked separately from static calibration. First confirm the system reads correctly under a slowly applied static reference force. Then apply a controlled load that rises and falls while Peak Hold is enabled. The captured peak should be consistent with the highest actual applied force within the dynamic limits of the indicator and fixture. Large differences may come from shock loading, vibration, sample rate, a loose fixture or a misunderstood hold mode rather than basic zero/span calibration.
Common calibration problems
Scale will not return to zero: unload the cell completely, check binding and cable pull. Reading is stable but wrong by the same percentage: verify the span value, engineering units and gravity setting. Reading changes when the fixture is touched: inspect mounting alignment and electrical shielding. Reading is correct at one load but wrong elsewhere: check nonlinearity caused by mechanics, an overloaded/damaged sensor or an unsuitable calibration point. Display is noisy: isolate vibration, inspect connectors and power, and make sure the cable is not routed next to strong electrical noise sources. Compression and tension disagree: inspect the fixture for backlash, side force or different load paths in each direction.
How often should it be checked?
Verification frequency should match the consequence of an incorrect measurement. A casual maintenance comparison may only need periodic checks, while production quality, proof-load or traceable test work may require a documented schedule and calibrated reference standard. Always recheck after overload, impact, sensor replacement, cable repair or a major fixture change.
Return to the complete MS720-15K guide for specifications and applications.
Where to buy
MNM Scales sells the MS720-15K as a calibrated 15,000 lb x 2 lb tension/compression package. Ask MNM to confirm the exact indicator model supplied if you need a model-specific service manual or button sequence.
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