Doosan 10/370, Operation And Maintenance Manual

Page: 85 / 96

Electrical Operating & Maintenance Manual
85
Sensors and Transducers
The electronics system contains sensors and transducers that are used to collect process data
from the compressor. The temperature is measured by a thermistor. This device exhibits a
change in resistance as the temperature changes. The resistance causes an input voltage
change to the WEDGE controller input and is interpreted as a temperature change.
The electronics system also uses pressure transducers to measure process pressure
changes. These devices have an output signal of .45V DC to 4.5V DC, corresponding to 0 psi
and the maximum measured psi for a particular device. The maximum pressure transducer
ranges are 100 or 225 psi. The 100 and 225 psi devices are gauge pressure devices. These
transducers are provided with 5V DC excitation to power the device. These are three wire
devices: excitation, signal and ground (return) connections.
Digital Inputs and Outputs
The WEDGE controller scans digital inputs such as switch contacts. These are either “ON”
(24V DC) or “OFF” (0 V DC). These digital inputs are connected to switches within the package
such as the key start switch, air filter switches and IQ filter switches.
The WEDGE controller provides 24V DC digital outputs to control solenoids, start compressor
and DC heaters. These are 24V DC “ON” and 0V DC “OFF”. They are current limited and short
circuit protected.
Controller Outputs:
The WEDGE controller has three different types of outputs: frequency, pulse width modulated
(PWM) and 24V DC digital (ON/OFF). The frequency output is used as a throttle signal for the
engine.
The PWM signal is used as a throttle signal for the Caterpillar engine. It has a base frequency
of 500 Hz and the duty cycle varies from 10% to 90%.
Pressure Control
The discharge pressure is controlled by manipulating the engine speed and compressor inlet
valve position. The inlet valve position is controlled pneumatically and the engine speed is
determined by the WEDGE controller. The WEDGE measures the pneumatic system
regulation pressure and computes an engine throttle setting. This throttle setting is sent to the
engine via the frequency throttle, PWM or J1939 throttle, depending on which technique is
used. The engine controller will control engine speed to this throttle setting.