Loop Info-Q-2-16
13
SECTION 4 - TROUBLESHOOTING LOOP SYSTEM
Loop Diagnostics
Proper installation of the loops is essential for reliable functioning of the detector system. Loop detection systems, when
properly installed, will provide one of the most reliable forms of vehicle detection available. Many loop system problems are
caused by poor connections, splices, incorrect type of loop wire, or the loop wire shorting to ground all of which will cause
intermittent operation or complete failure.
DoorKing loop detectors have a provision that provides loop diagnostics, which identifies if a
problem has occurred in the detection system. The red surface mounted LED (L1) on the loop
detector will illuminate when the detector senses a vehicle presence, and will go out when the vehicle
leaves the field of sensitivity. If any problem occurs in the underground loop, lead-in cable, or in any
of the connections, this LED will go into a fault mode by flashing. If the problem is a short or an
intermittent poor connection, which corrects itself, the detector will return to normal operation,
however the LED will continue to blink until it is manually reset or until power is removed from the
system. If the LED is blinking, even if the detector is working properly, a problem exists and checks
should be made for poor connections or shorts to ground.
The loop wire shorting to ground is a very common problem. This is especially true when PVC wire
(THHN, TFFN, etc.) is used for the ground loop or a splice was made underground. These type of
problems will often cause problems when moisture is present. If there is a nick in the wire insulation, the
loop will work when the ground is dry, but when moisture is present (rain, sprinklers, morning dew, etc.),
the nick causes a short to ground. This can be checked by utilizing a megohm meter capable of testing up
to 500 megohms (500 million ohms), such as a DoorKing meter P/N 9401-045 (A typical ohms meter will
not read units as small as micro henries). Disconnect the loop wires from the loop detector. Place one of
the meter leads to the loop wire and the other to earth ground. Resistance should be greater than 100
megohms. If resistance is between 100 and 50 megohms, the wire insulation has been nicked and the
integrity of the loop is questionable. If the resistance is less than 50 megohms, the loop wire will have to
be replaced.
Poor Connections
A poor connection from the loop to the loop detector will generally cause an intermittent problem where the loop will “false call” or “lock on”.
Often a crimp connection, wire nut, or similar type connector will operate when they are originally installed, but after a period of time the wires
may corrode, or the connection will loosen. Vibrations from gate operators can cause these loose connections to be intermittent and generate
false calls, or lock up the detector. Remember, the power through the loop is very low and does not have enough power (like 110 volt
connection) to go through any type of corrosion or loose connection.
Be sure that all connections are soldered.
Shorted Loop Wire
Loop Detector Adjustments
•
Sensitivity sets how much moving metal must be present
for the detector to send an output.
•
Sensitivity Boost increases sensitivity by a factor of ten
once a vehicle is detected. This locks in high bed trucks.
•
Frequency sets the operating frequency of the loop. When
two loops are operating in close proximity to each other,
the frequency on each detector should be set differently.
The loop with the longest length of wire should be set at
the lowest frequency.
•
Frequency Counter - Blinks out frequency on L1 LED when
the detector is powered up or reset button has been pressed.
9410
Manual
Reset
L1
Frequency
Sensitivity
9410
L1
20
BAD
CAUTION
MEGOHMS
40
60
100
150
200
300
400
700
ON
Megohmmeter
M500
M500
1000
ABOVE 1000
NO LIGHT
BELOW
Summary of Contents for 9409 Dual Channel
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