Mettler Toledo Troubleshooting
By Katrina Arthurs
The Mettler Toledo VLF is a low-profile, fully electronic factory-calibrated floor scale. Designed for dry industrial and commercial weighing, the Mettler Toledo VLF is not suitable for immersion or exposure to liquids or corrosive chemicals. When the scale fails to work properly, the cause can be either mechanical or electrical.
Prior to Troubleshooting
Examine the scale and the surrounding area for any standing water. If you find any, quickly dry the scale.
Look for any corrosive materials on the scale. If any are present, determine the type of material and clean the scale accordingly.
Check to be certain the floor underneath the scale is level. If it is not, the scale will have to be removed and the floor leveled before reinstalling the scale.
Check for wind currents and strong vibrations in the vicinity of the scale. In most cases, these factors are uncontrollable, and the manufacturer recommends the scale be reinstalled in a location away from wind and vibration interference.
Inspect the scale for any physical damage to the frame and platform. If damage is present, complete troubleshooting to ensure that there is no other damage, then consult the owner's manual for replacement part information.
Shut the power off and unplug the power supply cord. Disconnect the scale from the terminal.
Test the terminal by connecting it to a load cell simulator. If the problem persists, the terminal voltage will need to be checked. If the problem resolves itself, the cause is in the scale. Wiring and load cells will need to be checked.
Disconnect power to the system.
Unscrew the access panel cover plate on the scale platform.
Inspect the junction box for foreign materials and moisture.
Ensure that insulation material is not touching the terminal contacts.
Ensure that all wires are properly connected to the correct terminal. Tighten any loose connections.
Disconnect the power and check each load cell for proper input and output resistance. Refer to owner's manuals for exact resistance ratings.
When resistance ratings are within specifications, perform a shorted signal symmetry test. Short the signal leads together. Place one multimeter lead on the +Excitation wire and another on the shorted signals. Take resistance value, then remove the +Excitation lead and attach it to the -Excitation wire. Take the resistance value. The two values should be approximately equal.
If the load cells pass the signal test, repower the scale and confirm that proper excitation voltage is reaching the cells. Attach multimeter leads to the excitation positions on each load cell terminal. If the terminals pass, check each cell output signal.
The maximum output possible is 45 mV. If a cell has particularly high or low output, it is suspected to be the problem and should be replaced.
Katrina Arthurs began her writing career in 1999. She served as a columnist for the "Edgewood News Herald" then as a reporter and production manager for the "KC Conservative." Arthurs is pursuing her Bachelor of Science in criminal justice at the University of Central Missouri.