Adam Equipment CBC Series Service Manual page 12

10 VOLT POWER
SUPPLY
+S
This will cause the bridge to become unbalanced. When the bridge has a voltage across it
from +E to -E then the signal output at +S and -S will show a voltage of zero volts with no load
and a small voltage proportional to the load as the load is increased. Typical load cells show
20-30mv of signal if the excitation voltage is 10volts and the load cell is fully loaded.
Most load cells used in scales are not as simple as this example. They have additional
resistance elements added to compensate for temperature variations and to set the outputs to
correct voltages. The circuit of a typical load cell is shown below.
A method to check the basic function and integrity of a load cell can be done using an
ohmmeter and voltmeter with up to a 10volt power supply.
@Adam Equipment Company 2005
+E
A
B
-S
C
D
Vout = O VOLTS,
BETWEEN +S AND -s
-E
BALANCED BRIDGE
10 VOLT POWER
SUPPLY
+S
12
+E
A
B
-S
C
D
Vout = 0.028 VOLTS (28mv),
BETWEEN +S AND -s
-E
UNBALANCED BRIDGE
FULL CAPACITY LOAD
ON THE LOAD CELL