How do I verify my scale system is balanced?

The following is an process outline to verify that a scale system is balanced. Performing this process will help your scale system provide accurate and repeatable weight readings. Load sharing is important to ensure stability of the vessel and scale. Any imbalance between load cells would have to be very dramatic to make the scale unstable.

An example would be standing on a floor scale and shifting your weight left and right, to see if this action caused a rocking motion in the scale base. This would be an mechanical instability that would be solved by adjusting the corners feet height or adding shim stock. Normally the imbalance is caused by motors and other attachments to the scale, requiring counter balances to keep a scale vessel upright.

You will see there is always some difference from load sensor to load sensor.  These can be very slight differences due to the construction of the load cell to motors and other appurtenances that apply extra load to a load corner.

Using a multi-meter, check connector J1 on your Hardy weight controller load cell connector. If your instrument has Integrated Technician the measured values can be read over the front panel display, the embedded web server or via a PLC HMI.

1. Confirm the excitation voltage. Measure from +EXC to -EXC.

a. 10 volts DC (HI 2151/20WC, HI 1771WS, and HI 2160 RC).

b. 5 volts DC (HI 2151/30WC, HI 1746WS, HI 1756WS, HI 1769WS, HI 200DNWM, HI 4000 series, HI6000, and HI 3000 series)

2. Confirm the millivolt signal is a POSITIVE millivolt reading. Measure from +SIG to -SIG.

a. 0-30 Milli volt (mV) on the HI 2151/20WC, HI 1771WS, and HI 2160 RC

b. 0-15 Milli Volt (mV) on the HI 2151/30WC, HI 1746WS, HI 1756WS, HI 1769WS, HI 200DNWM, HI 4000, HI6000, and the HI 3000 series.

3. Load sharing includes load cell operation and verification.  Aonther web tech answer ID 72 goes into greater detail in determining the correct mv change.

a. Assuming the load cell wiring is complete and correct, apply weight. Does the mV signal increase?

b. A negative signal reading on the connector indicates the load cell is, miss-wired, upside down or defective. Verify the load cell installation manual for correct installation.

c. Load cells in tension will not reflect a negative reading if installed upside down. If upside down, the force applied by the cable would interfere with the weight readings.

4. If your vessel has multiple load cells verify all the mV readings individually. Reading the signal with all the load cells plugged will provide you a summed millivolt reading.  (target value)

            a. Disconnect the signal side of the load cell cables.

b. Verify a positive reading from each load cell.

c. Record the mV readings and compare each corner for proper load sharing.

d.  At the summing junction box with the controller powered up and all the wires connected, read the summed millivolt signal.  This is your balancing target signal level for each load cell.