3M C1060 Manual page 87

# # # #
Intercom Accessories
All Models using Vehicle Detectors
Technical Bulletin 12/3/98
Installing a Sonic Detection Alert Vehicle Detector
(78-6911-4432-9) using only three wires when four wires are not
available
Description:
Thanks to Brad Wolfe from Midwest Systems and Services Inc., Fort Wayne, IN for this suggestion.
This modification eliminates the need to run two additional wires though the conduit to the menu sign
when replacing a defective loop or sodar detector with a sonic detector. Normally, the sonic detector
requires four wires, two wires to supply 12 Volts AC for power and two wires to supply a switch closure
to the intercom. We recommend using four wires when possible.
The sonic detector will perform equally well on 12 to 20 Volts DC, which is available on the switch
closure wires from the intercom. Therefore, this available DC voltage and an additional ground wire,
normally found as a shield on an audio cable, are all that is needed to operate the sonic detector.
Parts needed:
1 each, 3M Sonic Detector (78-6911-4432-9)
1 each, 1000 microFarad, 25 Volt capacitor (optional)
2 each, 1 inch lengths of shrink tubing or wire insulation to insulate the capacitor leads.
1 each, 1 inch jumper wire, 22 – 18 gauge
Procedure:
Follow the mounting instructions included with Sonic Detector. The 12 VAC plug-in transformer,
included with the sonic detector, is not needed.
For the following steps use the wiring diagrams attached to this bulletin.
1. Connect the optional capacitor positive lead and one end of the jumper wire to TB1, Pin 1. Make
sure to insulate the capacitor leads and tuck it in toward the board so the unit will fit back in the
electrical box.
2. Connect the optional capacitor negative lead and the shield from the microphone cable to TB1, Pin 2.
3. Connect the other end of the jumper wire and the +12 to 20 Volts DC supply wire from the intercom
to TB1, Pin 3. Remember that polarity is important.
4. TB1, Pin 4 is not used.
5. Connect the "Vehicle Detect" input wire from the intercom to TB1, Pin 5. Remember that polarity is important.