CONTROL MODULE CIRCUITRY

TM 10-6665-297-13&P 1-3 CONTROL MODULE (continued) 1-3.1 CONTROL MODULE CIRCUITRY. All models have circuitry to perform the following functions: (1) Supply regulated power to detector(s) (2) Signal detector power circuit failures (3) Receive detector electrical (gas analog) signal inputs (4) Compare signals with internal reference voltages to trigger warning and alarm signals in response to excessive gas concentrations at the detector(s) (5) Simulate gas signals for control module circuitry self-test in response to operation of the TEST pushbutton (6) Reset '"latched" warning and alarm internal relays by operation of the RESET pushbutton The function and operation of the various internal circuits incorporated for these purposes may be described as follows (See Figures 1-4 through 1-7.): 1-3.1.1 Power Supply. (Figure 1-8) Line voltage at 115 or 230 volts, 50/60 Hz, at 0.1 amp is transformed to a nominal 12 VAC input to the power supply, where it is rectified in a diode bridge rectifier component (U1 for CD800/830; U6 for CD802/832) within 1 percent in a miniature voltage regulator (U2 for CD800/830; U5 for CD802/832) when the power to the module is on (glowing green pilot light on panel). DC input terminals are provided for connecting directly to a 12-volt battery where desired. Both line and battery power may be connected simultaneously, with the battery on standby duty in the event of line power failure. The control electronics consumes approximately 15 watts of power. Two outputs, at nominal 13-volt and 6-volt levels, are provided from the power supply. A 100-ohm potentiometer (R2) in the 6- volt supply permits output voltage level adjustments to compensate for line voltage losses in conductors to and from remote detectors. 1-3.1.2 Signal Amplifier. (Figure 1-9) The signal amplifier circuit consists of a differential amplifier (U3 for CD800/830; U1 for CD802/832) and associated components, connected to signal and reference voltages. With fresh air at the detector, both amplifier inputs remain at a nominal 3.5-volt operating level. Therefore no voltage difference appears and no amplification occurs. Catalytic oxidation of a combustible gas on the detector sensor element, however, increases the temperature and thus the resistance of the sensor element, resulting in a voltage imbalance in the bridge circuit of which the 23-9617 7/1/76 1-7