Why doesn't my Hardy Instrument return to zero?

We have a weighing system that uses a Hardy weight controller that shows 52lbs when the tank is empty.  How do you zero that weight out?

There are several reasons why your weight would not return to zero.  They include, but are not limited to:
1. Loss of calibration.
2. Material still in vessel.
3. Binding on your scale.
4. Damaged load cell.
5. Damaged or corrupted controller memory.  

Doing a zero or calibration command without knowing why there is an error could mask problems and make the scale inaccurate. The first thing you should do is verify your scale is actually empty. If you can place a weight on your scale, and then remove it and it always comes back to the same reading repeatably, your calibration is probably off.  A re-calibration would be in order.

If the scale does not repeat the readings, then you probably have a mechanical binding issue with the scale and it needs to be corrected before the scale will work properly. Look for cables, conduit, pipes, flexures, hoses, etc. that can affect your weight reading and cause non-repeatbility.

If you decide you need to do a calibration, you may need to do both the Cal Low and Cal High (or a C2® calibration if you have Hardy C2® load cells).  If you do a Cal Low, you may verify the scale by placing a known weight on the scale.  If it reads correctly, you would not need to do a Cal High.  If the reading is incorrect, then a Cal High would need to also be done.  C2® calibration is a one step calibration and would work fine as long as there are no mechanical issues with the scale.

The zero command will cause the gross weight to read zero.  If you decide you just need to run the zero command, you need to verify you are within the zero tolerance settings.  When the zero command is run your Hardy controller will look at the gross weight reading, add this to any weight that has been zero'd off previously, and compare this total to the zero tolerance.  If it exceeds the zero tolerance, it will fail the command and not change the weight reading.   

If you are running in the Net Weight mode, then you should be using the Tare command.  The tare command will cause the Net weight to go to zero.  This will not effect the gross weight reading.

NOTE:  Verify your scale is not indicating motion. If your scale indicates it is in-motion, the zero command, tare command and calibration commands will fail.