Belt scales and recalibration: why, exactly?
After a belt scale has been installed and calibrated in an application, your job is not over –it is important to recalibrate the beltscale periodically. Note: Performing regular recalibrations gives the application the highest potential for accuracy.
Why do beltscale recalibrations?
There can be many reasons as to why a recalibration should be performed. It can be as simple as temperature or weather changes, maintenance to the conveyor or build up on the weighbridge, belt or rollers, anything that has the ability to change the effects of the material on the weighbridge.
How to perform a recalibration
The first step of the calibration is verifying the speed of the conveyor. This can be accomplished by using a tachometer or marking the belt at a known linear measurement and timing that section of belt. Using the numbers you obtained you can calculate the belt speed.
The second step is to perform a routine zero. With the belt running follow the steps outlined in the manual for your integrator (if needed) and perform a routine zero. What you would ideally like to see is a small percentage deviation. This step should be repeated at least three times to confirm repeatability. Once you are satisfied with the repeatability of the zero deviation, you should follow the steps in the manual to accept this deviation.
The third step is to perform a routine span calibration. With the calibration mass applied, follow the steps outlined in the manual for you integrator. What you would ideally like to see is a small repeatable span deviation. Repeat this step at least three times to ensure the percentage deviation is repeatable. Once you are satisfied with the repeatability of the span deviation, you should follow the steps in the manual to accept this deviation.
This would complete a routine calibration.
1. If during any step of your recalibration you receive non-repeatable deviations, it is important to investigate what is causing this. Simple accepting these deviations could introduce an error into the system potentially caused by a mechanical problem.
Possible Mechanical Problems
2. If you receive “calibration is out of range” while completing a routine zero or routine span on your integrator, this means you are more than 12.5% deviated from your initial zero or span. It is important to determine what is causing this error.
A careful inspection of the weighbridge should be completed to make sure the loadcells are able to deflect with load. The best way to determine if the scale is actually deflecting and the loadcell integrity is operational is by using the diagnostic parameters.
Possible Zero and Span “Calibration out of range” problems
If you find the reason for the error, correct it, and perform a new routine zero or span. If you have proven the system is working properly, perform an initial span or Initial zero.
Routine calibrations should be part of any belt scale maintenance schedule. There is no set time period recommended for routine calibrations; however, it is safe to say you need to look at your application and devise a schedule. In general the more demanding your application and setting, the more often routine calibration should be completed.
Belt scale systems have been providing accurate reliable service to our customers for many years, but performing technically sound routine calibrations to these systems can potentially give the best accuracy in any application.