Plow UP-Down Sensor Installation

Plow UP/Down Status Sensor
The CompassCom AVL System has the capability to report the status of a
plow’s blade in real time to the dispatch center. To accomplish this, a sensor
that switches on or off depending on the plow up/down status must be
installed. The sensor of choice is a magnetic proximity switch from Peperl
Theory of operation:
The Sensor is very simple to operate. When powered, it either detects the
presence of metal in front of it or not. The advantage of using magnetic
detection is that ice and snow build up on the sensor will have no effect on
it’s ability to sense the presence of metal in front of it. Conveniently, this
sensor has an onboard LED to alert the installer when it is detecting metal
making it very simple for the installer to know if the device is mounted
properly. The sensor will most likely be mounted on the bumper of a truck.
By positioning an angled bracket on the plow device to move in front of the
sensor as the plow blade moves up or down, the discrete status of the blade
can be reliably sensed and reported to the AVL System.
Physical Considerations:
The sensor is a ruggedized, corrosion resistant device that is made to
withstand the rigors of operation outside in the harsh environment.
However, care should be taken to minimize the amount of punishment the
sensor will be exposed to.
The sensing distance is .5 inches. This means that the piece of metal
moving in front of the device must be closer than ½ inches. This may seem
a bit close but a short sensing distance practically eliminates the chance of a
“false alarm” caused by vibration or other metal components nearby.
Wiring Diagram: CalAmp LMU 4200
The LMU 4200 has a 22 Pin I/O connector. It pins out as follows:
Header (looking into LMU)
The Pins of relevance are:
Pin 1 (Blue) – Input 1
Pin 2 (Orange) – Input 2
Pin 3 (Purple) – Input 3
Input wiring plugged into LMU
The proximity device has a 10 ft cable bundle with 5 colored wires. Four of
these wires will be used.
BLACK – Ground (Vehicle Battery Ground)
RED – Power – Should be 12 volts DC (Battery Supply)
WHITE – Common – Should be connected to +12V
ORANGE – Normally open switched wire. Connect to Inputs
When correctly wired and mounted, the orange wire will switch to +12V
when metal is place in front of the sensor. The LMU will detect the state
change from low to high voltage. When no metal is in front of the sensor,
the switch will be open and the LMU Input will NOT be at +12V. This
action can be reversed if the Blue, Normally Closed, wire is connected to the
LMU Input.