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I-1.1. F. Channel PC Card <br />Depending on the model selected, a Leak Alert system can accommodate up <br />to 4, 8, or 16 sensing probe channels. Functions of each channel is <br />controlled independently with a PC card, plugged directly into the edgecard <br />connector on the motherboard. <br />Each channel PC card can be used to control one liquid sensor and one <br />vapor sensor. An optional electronic module is available for converting the <br />vapor sensor signal into a zero to 1 volt or 4 to 20 MA analog output. <br />Each channel PC card also provides mounting of three LED indicators for <br />power, liquid and vapor alarms, and trimpots for liquid alarm, vapor alarm, <br />and optional analog output zero and sensitivity adjustments. <br />11.1. G. Zener Safety Barriers <br />The Zener Safety Barrier is employed to provide safe interfacing between the <br />sensors and the control electronics. More specifically, one side of the zener <br />barrier is connected to the motherboard wiring terminal while the other side <br />of the barrier is connected to the sensor lead. The maximum voltage (in case <br />of an open circuit) and maximum current (in case of a short circuit) is <br />limited by the zenor voltage and built-in resistance within the zener barrier <br />package. <br />llw�qrvjlll <br />liquidThe sensor uses a thermal element enclosed inside a i dia x i • • r <br />cablehousing. The sensor assembly is equipped with a 25 -Ft. PVC jacketed 2 -conductor <br />green . • black • •code. <br />The sensor can be installed in any orientation, and works for most liquids. <br />The vapor sensing probe uses a metal oxide semi -conductor (MOS) sensor enclosed <br />inside a 0.75 -in dia x 0.9•in long housing. The assembly is shipped with a 25 -Ft. PVC <br />jacketed 3 -conductor cable with red, white, and black color code. <br />11.4. SYSTEM ELECTRONIC CIRCUIT <br />The Leak Alert system electronic wiring diagram is shown in DWG No. 84-1010. It <br />can be divided into the following subgroups: <br />(a) Motherboard Wiring <br />(b) Base Plate Wiring <br />(c) Front Cover Alarm Circuit Wiring <br />(d) Channel PC Card Wiring <br />The 115AC power is connected to the terminal block mounted on the base plate. <br />This AC power is then connected to the master switch, the fuse, and then to the <br />— 3 — <br />