DSP-10 User Manual
Page 17 of 26
DSP10_MAN_C
9. The approximate inductance of the lead-in cable can be calculated using a value of .22 µH per foot for
lead-in cable.
100’ x .22 µH = 22 µH of inductance in 100’ of lead-in cable.
10. The ratio of loop inductance to lead-in inductance should be 2 to 1 for a well-designed installation.
Since the vehicle to be detected can only influence the loop inductance, letting the lead-in inductance
get close to the loop inductance will effectively lower the sensitivity of the loop. This is usually only an
issue when the loop is 50’ or more away from the detector. If you do have a long lead-in, additional
turns should be added to the loop until the 2 to 1 ratio is satisfied.
11. The ideal loop inductance is 50 to 500 µH. Although the detector will tune to loops in the range of 20 to
1000 µH, the 20 to 50 range should be avoided to provide a more stable loop and loss of sensitivity due
to lead-in inductance. It is always better to have too much inductance than too little.
12. Lead-in wires must be twisted. Ideally, 3 to 6 twists per foot should be maintained. It is also important
that the twists are tight. An air gap between the two wires should not exist as this can cause loop
stability issues. The lead-in wires should be kept twisted until right before connection to the detector.
13. A figure 8 loop can be used in locations where electrical interference is expected or seen. This is a
standard loop with an extra saw cut down the middle of the loop. This extra saw cut should point
toward the source of the interference as much as practical. If the source is overhead or below ground
(power lines) the saw cut should be parallel to the short side of the loop. The loop wire is placed in the
saw cuts using a figure 8 motion. A figure 8 loop will have more inductance that a similar sized
conventional loop.
14. If multiple loops are to be connected to the same detector there are several things to be aware of:
a. Always connect multiple loops in series. This increases the inductance and insures that a loop
failure will cause a loop fault at the detector.
b. The loops connected together
must
be the same size and the same number of turns. Failure to
do this will lead to the loops having different sensitivities that cannot be compensated for. This
difference in sensitivity can very large.
c. Connecting two loops together will reduce the sensitivity of each loop by half.
d. If the two loops are within 6’ of each other, the phasing of the loops should be considered. If
the loops are on the same side of a gate and are being used to increase the size of the detection
zone, the two edges closest to each other should have opposite phasing (North to South). This
will increase the sensitivity in the area between the two loops. If the loops are on opposite
sides of a gate, the loops should have the same phasing (North to North). This will decrease the
sensitivity in the area between the two loops. Especially at the middle point between the two
loops, it may be impossible to detect any object in this area. So, this phenomenon can be very
useful in sliding gate and lift gate installations.
Detector Installation
Location:
The detector should be plugged in to the appropriate connector on the DoorKing operator.
Mounting:
The detector will function when mounted in any orientation. Using the two holes in the detector,
secure the detector in place.
