DSP-22-1 User Manual
Page 20 of 22
DSP-22-1_MAN_D
If a loop is connected to the correct screw terminals of the detector, disconnect the loop and using an ohmmeter,
check the resistance of the loop circuit. If the resistance is below 0.2 ohms there is a short in the loop circuit. The
resistance will typically be 0.5 ohms to 1.5 ohms.
If the resistance is above 0.2 ohms, the loop inductance should be checked. This is done using an inductance
meter. The inductance of the loop should be more than 20 microhenries. If the loop inductance is less than 20
microhenries, the loop was probably not wound correctly and only has one turn in it. In this case the loop must
be replaced. Other possibilities include a foreign object embedded in the saw slot and shorting some or all of the
wires, or failed wire insulation due to the wire being exposed or the wrong type of wire being used. Very small
loops may also have a low inductance value if sufficient turns were not added. Contact technical support for help
with very small loops.
If you do not have a meter capable of measuring resistance and/or inductance but do have another operating
detector, you can skip to this step. Swap the loops between a working detector and a failing detector. If the
problem follows the loop the loop is the problem. If it stays in the same detector, replace the detector.
Detect LED Flashes at the Same Time as the Power LED every Two Seconds
This flash rate indicates that the channel has had a failure of some type but is currently working correctly.
Intermittent failures are usually open loop failures. Any splices in the loop wire should be redone. If there are
any wire nuts used in the loop circuit, remove them, and replace with a crimp connection or preferably, a soldered
connection. The open loop fault could also be a fatigued point in the loop wire. This can occur at locations where
the loop wires cross an expansion joint in the road surface. Any place where the loop wires must move, even if
only a very tiny amount, can cause wire fatigue. The actual failure point may be very difficult to find. Often the
loop must just be replaced if the issue persists but cannot be found.
It is possible for the intermittent failure to be a shorted loop fault. One possible source of this type of fault is a
foreign object being embedded in the loop saw cut and damaging the wire. Another is that the loop wire has been
damaged where it enters or exits a conduit or junction box, or that a conduit that the loop wire is in has been
damaged (crushed, kinked, bent, cut, etc.).
Power LED Intermittently Comes On (Not Once Every 2 Seconds)
This type of display is an indication that the detector is experiencing electrical interference. This could be cross-
talk with another loop connected to a different detector or an external source of noise. These external sources
can be radio transmitters, card readers, or any electrical device that is within several feet of a loop.
Detect LED Intermittently Comes On / Stays On Without a Vehicle Present
This type of symptom is usually caused by one of three issues: physical issues with the loop, electrical interference,
moving objects in proximity to the loop.
Physical Issues with the Loop
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There are many ways in which a loop installation can go bad. The insulation of
the loop wire can fail. This can be due to the loop wire being exposed in the saw lot, damage to the wire insulation
