
U Series Farm Bars
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6.0 Troubleshooting
6.1 General
If having trouble with the Farm Bars, perform the following procedures to diagnose the problem. First, inspect the scale for any
physical damage. Take special note of the cable and connectors. Wiggle the cables and connectors while watching the indicator
display. If the readout jumps while moving a cable or connector, there is likely a short or loose connection. Repair or replace the
cable or connector as appropriate.
6.2 Drifting
If the scale readout is drifting, moisture may be present in the scale's electrical circuit. Check for moisture in any of the
connectors, junction boxes or Farm Bars. Dry any location where you suspect moisture is present. If there is a location where
moisture is collects frequently, seal the location with a waterproof sealant.
6.3 Abnormally Large Reading
If the indicator shows a very large number and the readout cannot be changed using the indicators zero adjustment, there may
be a problem in the circuit. To locate this type of problem, a series of electrical resistance measurements must be made. To
perform these checks, an accurate ohmmeter and a soldering iron is required.
To locate a faulty component with the ohmmeter, start by measuring pin resistance in the connector that plugs into the indicator
cable (the cable that runs into the scale). The connector has four pins labelled A, B, C and D, the following chart lists the
appropriate resistance readings. Remember, when measuring pin resistance the power must be OFF. Ensure fingers do not
contact ohmeter probes otherwise measurement may be incorrect.
IMPORTANT: This table is only valid at a temperature of 71.6°F (22°C). Resistance will vary slightly with temperature.
The readings in Table 6-1 should be within 5 ohms of the value shown. The readings are slightly temperature dependent and as
a result will not match Table 6-1 exactly. However, all measurements should differ from the table by the same percentage. For
example, if the resistance across pins D and C reads 142Ω ±1Ω, resistance across pins D and A should also read 142Ω ±1Ω.
Specifically, the values equal in Table 6-1 should also be equal when you take your measurements. If the readings correspond
to the values in the table, an electrical problem in the scale is not likely. If any readings across pins of the connector differ from
the table, each load cell must be checked individually.
When checking an individual load cell, it must be completely disconnected from the scale's electrical circuit. To accomplish this,
the wires will need to be taken apart at the Farm Bar cable splice. See Figure 6-1 for the wiring of a Farm Bar system. The
circuit diagram for the load cells of a U Series Farm Bar system is shown in Figure 7-1 on page 15. Remember that each load
cell contains four wires. All four wires must be disconnected to separate that load cell from the circuit.
Take apart the cable splices and measure resistance across each of the load cells. The cell resistance should be 350Ω. If the
measurement for the cell is larger than 350Ω, or an open circuit, the load cell may have to be replaced. If receiving an incorrect
measurement from load cells I and II in the support bar, check the cable which connects the to bars for continuity.
Connector Markings Resistance Readings Load Cell #
A – C 395Ω
B – D 350Ω
A – B 263Ω I
B – C 308Ω II
C – D 308Ω III
D – A 263Ω V
Table 6-1. Ohmmeter Readings