LP600 Users Manual
Rev E, February 2017
Page 39 of 43
Schematic Diagram (typical values)
The 5 Ω thermistors in series with the Excitation leads are for temperature
compensation. They are balco thermistors that change resistance with temperature to
maintain a constant signal voltage. These thermistors are specially manufactured for
Intercomp load cell material and strain gage types.
Load cell leads color coding
Red : + Excitation (3.3 Volts)
Green : + Signal
White : - Signal
Black : - Excitation (ground)
Check load cell zero output value
The signal at the main circuit board with the signal leads in place should be
approximately 0.1 millivolts with no load applied to the cell. Larger values could indicate
a defective load cell, wiring, or circuit board. The load cell must be tested separately to
determine the source of the zero shift.
Check zero output from the load cell
You can use a power supply set to 3.3 Volts to provide the excitation voltage for this
measurement. Connect plus 3.3 volts to the red lead and ground to the black lead or
use the scale to provide the excitation by connecting the two excitation leads only
(Black and Red). Turn the scale on to apply excitation voltage.
Connect a meter capable of monitoring millivolt readings between the plus and minus
signal leads (Green and White) The zero signal output (With excitation voltage applied)
should measure approximately -1.00 to 1.00 millivolts). Larger values would indicate a
defective load cell. This is most likely the result of an overload of the cell during use.
Check load cell resistance values
Load cell resistance can vary depending on the model and capacity. The load cells will
be one of the standard resistance values given in the table below.
With the load cells disconnected, the resistance readings should be as specified. It is
normal for all of the readings to be higher or lower than the values given by several
percent. If there is several Ohm difference between the Black-Green and Black-White
measurements the cell is defective. This test is most useful to detect a catastrophic
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