Service Manual
DS 350 GM
Rev A 05/01/01 // SB
190113_A
46
6
THEORY
6.1
THEORY 1. OPERATION OF BOOM LENGTH SENSOR
The system sensors provide a 4 to 20mA output; however, due to
a fixed resistor circuit in the central unit, the input signal can be
measured using ammeter (current) or voltmeter (voltage). The
input signal operating window is 4 to 20mA, measured in series at
the analog input terminal OR 1.1 to 5.5V, measured in parallel
between the analog input and ground (GND) terminals. At 4mA the
voltage is 1.1V and at 20mA the voltage is 5.5V. When
troubleshooting this system, a current or voltage needs to be
measured to determine the status or condition of the sensor.
Measuring current:
The ammeter is used to measure current at the length input
signal. Remove the wire from X1:27 terminal in the central unit and
measure the current with the ammeter in series. The measurement should
be between 4..20mA.
Measuring voltage:
The voltmeter is used to measure voltage between pins X1:27 (length
signal) and X1:28 (gnd) on the main board (024-352-300-001 /
9333103287). The resistors are there to show that at 4mA the voltage is
1.1V because current multiplied with resistance equals voltage; therefore,
4mA x 275 ohms (total resistance) = 1.1V.
A
V
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