Midmark Patient Scale Repair: Inaccurate Readings & Load Cell Failure

A Florida clinic reported that their Midmark patient scale was providing readings that were under the correct weight. Accurate patient weight is critical for clinical assessments and medication dosing, so this issue required immediate attention. A PBES technician was dispatched to diagnose and resolve the problem.

Technician investigation

The technician began by attempting to correct the issue through recalibration. Following the manufacturer's guidelines, the scale was recalibrated. An initial test confirmed the weight was reading correctly. However, upon re-testing, the inaccuracy returned, and the displayed weight began to jump erratically. Suspecting a more serious hardware issue, the technician then tested each quadrant of the scale's load cells, observing varying and inconsistent numbers from all of them.

Root cause

Suspected: Intermittent failure of the internal load cells. The root cause was not definitively documented, but the erratic and quadrant-specific readings strongly pointed to failing load cells, making the unit unreliable and beyond simple recalibration.

• Improper calibration as the sole cause of failure

Resolution

The initial resolution attempt was to perform a full recalibration procedure according to manufacturer specifications. While this briefly corrected the readings, the problem quickly resurfaced. After further testing revealed unstable readings from the load cells in every quadrant, the technician determined the scale was not repairable in a cost-effective manner. It was recommended that the clinic remove the scale from service and replace it with a new unit to ensure patient safety and measurement accuracy. No parts were replaced.

Verification

• Calibration verification
• Performance testing with known weights

Verifying a patient scale's accuracy after any adjustment is non-negotiable. It ensures that critical measurements used for diagnosis and treatment are reliable. In this case, repeated verification testing is what revealed the intermittent nature of the failure, preventing the device from being incorrectly returned to service.

Technician insight

An experienced technician knows that when a scale provides unstable or 'jumping' numbers after calibration, the problem is rarely the calibration itself. This is a classic symptom of a failing load cell or related electronics. Testing individual load cell quadrants confirmed the hardware fault was not isolated, making replacement the only safe and reliable option.

Common Causes for Inaccurate Patient Scales

• Incorrect calibration or calibration drift over time.
• Physical damage to the scale platform or feet.
• Failure of one or more internal load cells.
• Debris or foreign objects under the scale platform.
• Interference from unstable surfaces or drafts.
• Internal electronic or mainboard failure.

In this specific case, the scale's inability to hold calibration and the jumping numbers pointed directly to a suspected failure of the load cells.

FAQ

Why is it important to test a scale after calibration?

Testing after calibration, often with certified weights, verifies that the adjustment was successful and the scale is accurate across its range. As this case shows, it can also reveal intermittent problems that calibration alone cannot fix.

What are 'jumping numbers' on a digital scale?

Jumping numbers refers to an unstable digital readout where the weight value fluctuates erratically without any change in the load. This often indicates a problem with the load cells or the internal processing electronics.

Can a patient scale's load cells be replaced?

In some models, individual load cells can be replaced, but it can be a complex and costly repair. For many scales, especially if multiple cells are failing or the model is older, replacing the entire unit is often more economical and reliable.

Was this Midmark scale returned to service?

No. Due to the unstable readings and suspected load cell failure, the PBES technician recommended the unit be removed from service and replaced to ensure patient safety.