TM 10-6665-297-13&P1-3CONTROL MODULE (continued)1-3.1.2 Signal Amplifier (continued)sensor is a part. A differential voltage then appears between the two amplifier inputs and amplificationoccurs. The resulting amplifier output is applied to the percent L. E. L. meter and to the warning, alarm,recorder, and failure detection circuits that follow.1-3.1.3 TestCircuit. (Figure 1-9) The test circuit is provided to simulate gas alarm conditions by pushbuttonaction. When the TEST pushbutton on the control module front panel is depressed, a circuit is closedfrom ground through potentiometer R22 to the + input of differential amplifier U3 of CD800/830 or U1of CD802/832. The result is an imbalance between the two inputs to U3 or U1 such as would be causedby the detection of a 100- percent L. E. L. gas-air mixture at the detector. A screw-adjustment setting ofthe RANGE potentiometer R22 controls the signal level to the amplifier to drive the indicating meter tofull scale with the TEST push- button depressed. Since the signal displayed on the meter is also afunction of signal amplifier gain, as established by the GAIN adjustment potentiometer (R10 forCD800/830; R9 and R13 for CD802/832), RANGE control R22 may require slight readjustment if thegain setting (U3 for CD800/830; U1 for CD802/832) is altered during a calibration check. When theproper setting of R22 has been made, the ALARM and WARN lamps and relays respond to operationof the TEST pushbutton as if in an actual alarm condition, so that the operation of the control modulecircuitry and external warning devices may be evaluated for purposes of maintenance.1-3.1.4 WarningCircuit. (Figure 1-10) The control module warning circuitry operates from the amplifieddetector output and an adjustable reference voltage. The reference voltage is usually set at a levelequivalent to an amplified detector signal representing a gas-air mixture of 20 percent of the LowerExplosive Limit (20% L. E.L.). Both the amplified detector output and the reference voltage are appliedto a voltage comparator (U4 for CD800/830; U3 for CD802/832). If the signal level is below thereference voltage, the base of transistor Q5 is negative, and Q5 is in the "off" state. When theamplified signal exceeds the reference voltage level, a positive voltage of sufficient magnitude to "turnon" transistor Q5 causes current to flow through the transistor to energize the warning light and relay.Any audio or visual warning devices connected to the relay output terminals may be controlled in thismanner. The warning reference volt- age level is set by means of a screw adjustment on WARNpotentiometer R26 for CD800/830 or R48 for CD802/832. Transient pulses are prevented fromenergizing the warning circuit by means of a time delay circuit described below.23-96177/1/761-14
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