Connections
– 10 pin MS 3102-A-18-P mating with MS3106-A-18-1S.
Pin #
Function
Color
C
Power
(+)
Black
A
Power
(-)
White
H
Chassis
Ground Green
B
Relay
Common Yellow
F
Relay
N.O.
Blue
G
Relay
N.C.
Red
D
Loop
Gray
E
Loop
Brown
I Spare
White/Black
J
120VAC Timer Override
White/Red
*
Note:
The above connection is shown with correct power supplied and no vehicle present.
Theory of Operation
Systems Description
The Northstar Controls NT11 and NT11-E sensor unit consists of the following major circuit
elements: The loop oscillator, the digital period measurement circuit, the microcontroller, the
front panel switches and indicators and the output circuits
The loop oscillator, when connected to a suitable road loop / lead-in combination, establishes an
oscillating signal the frequency of which is directly related to the inductance of the loop and
lead-in. When a vehicle enters the detection zone surrounding the loop, the inductance of the
loop changes causing the frequency of the oscillating signal to change and providing a means to
determine the presence of the vehicle. Transient protection elements are incorporated within the
oscillator to prevent large transients from causing damage to the oscillator or other electronics.
Frequency switches accessible from the front panel allow the operating frequency of the
oscillator to be modified to prevent mutual interference between oscillators associated with
different sensor boards connected to adjacent loops.
When a channel is energized, a sample of the frequency is taken and compared to a stored
reference. Sensitivity switches accessible from the front panel allow the adjustment of sensitivity
which determines the amount of change in frequency that is required between the current sample
and the reference to result in a detect call being made.
The detection call output for each sensor is made by means of a relay which is set to conduct to
indicate a vehicle detection. Front panel led indicators also indicate a vehicle detection and also
when the inductance of the road loop exceeds the operating range.
Page 6
Summary of Contents for NT11
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