Why is my zero weight reading incorrect or locking high? What is linear correction?

My weight reading does not start at zero with an empty vessel or locks at a high weight level. My contractor said something about linear correction. What exactly is linear correction and what are some indications of a poor linear correction?

Linear correction is not required is 99% of all scales and only after all attempts to correct the mechanical problem have been exhausted.  A mechanical problem that goes uncorrected will make the scale weight readings questionable.

Linear correction may be necessary when an error exists after the vessel has been calibrated and weight charted at set increments. During scale charting (normally at 10% increments), the point of maximum weighing error is found and deemed unrepairable due to a mechanical design problem. An example:

1. A test weight is applied to the scale equal to the weight found to have the greatest weight offset at 500 lb. (Example 500 lb = 530)
2. Install a 500 lb in test weight on the scale
3. Enter configuration and arrow to CAL, HDCAL, and LINCOR.
4. Enter the linear correction amount as 500.
5. The weight controller will now compensate the 30 lb difference at 500 lb.

Linear Correction is only available with the following instruments: HI 1771WS, HI 2110 WI, HI4050, HI 2151/30WC, and the obsolete HI 2151/20 WC. If your weight reading does not start at zero with an empty vessel or locks at a high weight level it is possible that your calibration was incorrectly applied to the linear correction settings under Hard Calibration. Linear correction is used to compensate for a repeatable mechanical scale system problem. Check the troubleshooting section of the Operation and Installation manual to help trace vessel instabilities and installation faults.  Linear correction is normally where the weight stops at a set weight an will not advance.

If your problem is that the scale doesn't start at zero, this could be a mechanical problem or the fact that your scale resolution is less than your display resolution. Let's say that you have a 10,000 lb scale. This scale should be repeatable +/- 1 lb. You shouldn't be using any decimal points and the scale may vary or drift +/-1 lb. To achieve better results would require mechanical inspection and fine tuning. Typically, this is the practical limit of the load cell system and if there is a requirement for a higher resolution a smaller capacity scale should be used for smaller batch amounts.

The next question:  The linear correction value cannot be larger than the span value.  The weight applied to calibrate the scale.


NOTE: Results using different combinations of span and linear correction weights to span weights.

Errors will occur if LINCOR is entered without weight applied or weight equal to or greater than the SPAN weight. (The SPAN values should be 80-100% of maximum live load.)

If the LINCOR weight value entered is equal to the SPAN weight WITH that weight applied, then the weight reading will stop increasing after the SPAN weight is reached.

If the LINCOR weight value entered is equal to the SPAN weight WITHOUT that weight applied, then the weight reading will jump to the SPAN weight value and remain there.

If the LINCOR weight value entered is less than the SPAN weight WITHOUT that weight applied, then the zero reference and top end weight readings will be offset by the LINCOR value and the weight readings will be nonlinear.

If the LINCOR weight value entered is greater than the SPAN weight with that weight applied, then the scale will read normally until the LINCOR value is reached, and then stops.