Lab balance: How to troubleshoot

laboratory balance

What do you do when your lab balance isn’t working?

Having trouble getting your lab balance to work properly? We have a few ideas for you to try that may save your balance and your science from stalling. The problem may not be as difficult as you think. For the smaller problems, you can fix it yourself. But when the issues get a little more complicated, it’s best to call a qualified service specialist.

Lab balance problems usually fall into one of the following categories:

User problems

You may be asking the balance for something it cannot do or is confused by the modes and functions of a balance. It is also possible you may have  set a parameter that has affected the balance operation. Resetting the parameter to a normal value will restore operation.

Mechanical problems

The balances consist of complicated and fragile mechanical devices. They can be damaged by placing a weight on it which is too high for the balance or by dropping the balance or occasionally shipping it without taking care. The most fragile parts are the flexures. Dust, dirt, spills and other foreign objects in the balance can also cause problems.

Electronic problems

These are the rarest of the problems affecting balances. If an electronic problem is suspected make sure the mechanical problems that can cause similar symptoms have been eliminated before attempting electronic repairs. With the exception of cables most electronic repairs are solved by board replacement.

Common problems and solutions

Use this table as a general guide for troubleshooting your lab balance. When you see an asterisk by a solution, you need to contact a qualified service specialist.

General Troubleshooting Guide
Balance does not function
Problems Possible causes Suggestions
The balance is dead when power is applied. Power supply failure Check to see if adapter is working.
Check that adapter is correct for the balance.
*Power supply circuit board failure
*Short circuit on any circuit board
The display does not turn on but the calibration motor moves when power is applied. Power is getting to balance, display is not working *Display cables may be faulty
*Display module failure
The display stays on the initial test screen when power is applied. Calibration weight motor is on. Unstable balance
Balance not working correct
Power supply
*Check if balance is stable by using service
menu and view A/D values.
Put draught shield over pan.
Check power supplies.
Balance works but is not stable
Balance is unstable by a few divisions. Noise or vibration from environment Friction in mechanics Check the balance is positioned correctly to avoid vibration, wind or air movement, it is on a solid table, It is not near sources of heat or cool air.
Check balance with weights if problem occurs when sample is used.
Static electricity on the samples can cause drifting and instability.
Check the area around the weighing pan for hair, dust, obstructions under the pan.
*A complete inspection of the mechanics to look for sources of friction may be needed.
Balance is very unstable and does not weigh correctly. Mechanical problems
Balance programming
Electronic problems
*A complete inspection of the mechanics to look for sources of friction.
*Verify the A/D is also unstable. If the A/D is OK then suspect the programming of the balance. Reset parameters, check linearity and redo the calibration. Some electronic problems can also cause this. But all mechanical problems must be resolved first.
Balance is not accurate
You must have accurate and trusted weights to test a balance. If you suspect that the balance is not accurate then you must know your weights are accurate. A balance calibrated using a bag of flour is not accurate even if it works OK otherwise.
Balance is not accurate Repeatability
Eccentric loading
Linearity
Verify the balance shows the same value when the same mass is placed on the center of the pan for a few tests.
Verify the balance shows the same reading (within a tolerance depending upon the model) when a mass is placed at positions around the pan.
Verify the balance is acceptable throughout the weighing range. The balance must give acceptable readings from low weights up to the capacity.
Poor repeatability Usually a mechanical problem Inspect the area around the pan for hair, dust or other obstructions.
*Inspection of the mechanics may be needed for any possible problems.
Poor eccentric loading A mechanical problem Inspect the area around the pan for hair, dust or other obstructions.
*Inspection of the mechanics may be needed for any possible problems.
*Readjusting of the Eccentric Loading is recommended.
Poor linearity Usually a mechanical problem
Electronic problems
Re-check repeatability
*Inspection of the flexures for damage or loose hardware may be required
*Use the Linearity Function in the service menu to reset linearity
*A problem in the analogue circuit board or power supplies can cause poor linearity. Make sure all mechanical problems have been eliminated first.
Other issues
Cannot calibrate Zero shifted more than allowed Calibration timeout *Check all flexures for damage.
*Reset dealer calibration.
*Verify linearity and repeatability.
*The balance may be unstable. Verify stability as above.
Calibration weight motor does not stop *Check the cables to the motor, try plugging the balance into the power again.
*Look for friction in the calibration weight movement.
*Check the opto-coupler that controls the motor position.
RS-232 not working Doesn’t print Check parameters match the device connected. Verify cable is correct.
*RS-232 circuits damaged
Display dark, keys beep Display contrast poor
Cable unplugged or damaged
*Check the cables to the display.
*Replace the display which could be damaged.
*To be carried out by authorized technicians only.

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