How to Calibrate the MNM MS-202 / PS-IN202: P11 Zero & P12 Span
- pete8781
- Jul 29
- 3 min read
For calibration help or the correct MS-202 replacement indicator, call MNM Scales at (832) 290-3120 or email mnmscales@yahoo.com.
To calibrate the MNM MS-202 / PS-IN202 scale indicator correctly, first make sure the weighing mechanism is mechanically free and the load-cell signal is stable, then use the documented P11 routine for unloaded zero and P12 for known-load span. Calibration cannot correct a bent platform, binding foot, wet junction box, damaged cable or overloaded load cell, so the mechanical and electrical checks come first.
Before Entering Calibration Mode
Level and unload the platform. Remove debris that can touch the deck or frame. Confirm each load-cell foot is carrying load normally. Check the cable and connector for damage. Allow the indicator and load cells to stabilize after power-up. Confirm capacity, unit, decimal position and division size are appropriate for the scale. If this is a multi-cell system, correct corner-response problems before final span calibration.
P11: Zero Calibration
With the indicator in the setup P menu, navigate to P11 and enter the zero-calibration routine with the ZERO key. The manual shows an internal A/D count after entering the routine; this value can help diagnose a setup problem. With no test weight on the scale, press ZERO again to establish the unloaded reference, then use NET/GROSS to save. The indicator should display the successful end message and return to P11.
P12: Span Calibration
Navigate to P12 and enter the span routine. Place a known test load on the weighing mechanism, then key the actual test-weight value into the indicator using the documented direction-key functions. Save the span point with NET/GROSS. The PS-IN202 documentation allows additional span points, which can improve confidence that the configured scale behaves correctly through its useful range. Use traceable or otherwise well-known test loads appropriate to the accuracy required by the application.
The manual states that the minimum calibration test load is 1% of full-scale capacity. A larger, accurately known calibration load generally gives more useful span information than a tiny fraction of capacity, especially on industrial scales, but the practical load must also be safe for the platform and test procedure.
Verify After Calibration
Remove the weights and confirm return to zero. Apply a low, middle and higher known load if available. Check repeatability by applying the same load several times. On a floor scale, move a suitable verification load to different corners to detect mechanical or junction-box balance problems. If the application is Legal for Trade, calibration alone is not a substitute for the inspection, sealing or local weights-and-measures procedures that may apply.
Common Calibration Errors
The PS-IN202 documentation identifies common calibration failures including a keyed or applied calibration value larger than scale capacity, a test load below the permitted minimum, and insufficient internal resolution for the requested configuration. If span will not accept, do not repeatedly force the menu. Recheck full-scale capacity, decimal/division settings, calibration units, platform signal and actual test weight first.
When Calibration Does Not Fix the Reading
If the system calibrates but drifts, changes when a cable moves, reads differently at each corner or will not return consistently to zero, investigate the load cells, junction box, mechanical frame and cable shielding. Calibration scales a healthy signal; it cannot make an unstable sensor or binding structure repeatable.
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