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22 Pelco Manual C690M-E (11/04)
Figure 8a. Supervised Alarm Operation
ALARM
ALARM
SUPERVISED, NORMALLY CLOSED
STAND-BY MODE
1.65V
3.3V
POINT A
TIME
POINT A
10K
+5V
+5V
0V
10K
10K
100K
0.1uF
0.1uF
GND
GND
GND
EQUIPMENT SIDE
ALARM
WIRING SIDE
INPUT
VOLTAGE
NORMAL
CURRENT FL0W
NO ALARM
VOLTAGE
DIVIDER
NETWORK
S
Processor
CIRCUITRY
GND
TTL-CMOS
EXTERNAL
CONTROL
<
_
50ms
PIN 1
PIN 2
IN THIS CONFIGURATION, TRANSISTOR "S" (THE SWITCH) IS BIASED FOR
CONDUCTION AND WIRED IN SERIES WITH ITS 10K COLLECTOR RESISTOR.
ALONG WITH THE INTERNAL 10K RESISTOR ON THE EQUIPMENT SIDE,
THEY FORM A VOLTAGE DIVIDER NETWORK THAT LEAVES POINT "A" AT
ABOUT 2.5V (WHICH IS MID-POINT IN THE "STAND-BY MODE" VOLTAGE
RANGE SHOWN IN THE ALARM DIAGRAM). A HIGH CONTROL SIGNAL (TTL)
GREATER THAN 50ms DURATION ACTIVATES NORMAL STAND-BY MODE.
ANYTHING THAT MAKES THE TRANSISTOR TURN OFF (EFFECTIVELY AN
OPEN) OR CAUSES A LOW CONTROL SIGNAL RESULTS IN AN ALARM
CONDITION AS POINT "A" GOES FROM 2.5V TOWARD 5V. SIMILARLY, A
SHORTED CONDITION MAKES THE VIDEO DROP TOWARD 0V AND AN
ALARM CONDITION.
NOTE: PIN NUMBERS
REFER TO TYPICAL
HEADER ALARM INPUT
NUMBERS ON MATING
PLUGS
NOTE: TIME DURATION
OF THE INPUT
CONTROL SIGNAL MUST
BE 50ms OR MORE
ALARM
ALARM
HIGH = STAND-BY MODE
LOW = ALARM
ALARM
ALARM
SUPERVISED, NORMALLY OPEN
STAND-BY MODE
1.65V
3.3V
POINT A
TIME
POINT A
10K
+5V
+5V
0V
10K
10K
100K
0.1uF
0.1uF
GND
GND
GND
EQUIPMENT SIDE
ALARM
WIRING SIDE
INPUT
VOLTAGE
NORMAL
CURRENT FL0W
NO ALARM
VOLTAGE
DIVIDER
NETWORK
S
Processor
CIRCUITRY
GND
TTL-CMOS
EXTERNAL
CONTROL
<
_
50ms
PIN 1
PIN 2
IN THIS CONFIGURATION, TRANSISTOR "S" (THE SWITCH) IS WIRED IN
PARALLEL WITH A 10K EXTERNAL RESISTOR. THIS PROVIDES A VOLTAGE
DIVIDER NETWORK FOR NORMAL, NO ALARM (STAND-BY) OPERATION AT
ABOUT 2.5V AT POINT "A." IF CURRENT FLOW STOPS, VOLTAGE RISES
TOWARD 5V AT POINT "A" AND AN ALARM CONDITION. IF A NORMAL ALARM
CONDITION OCCURS AND THE TRANSISTOR CONDUCTS (SWITCH
CLOSES), A SHORT RESULTS AND POINT "A" FALLS TOWARD 0V AND AN
ALARM CONDITION.
NOTE: PIN NUMBERS
REFER TO TYPICAL
HEADER ALARM INPUT
NUMBERS ON MATING
PLUGS
NOTE: TIME DURATION
OF THE INPUT
CONTROL SIGNAL MUST
BE 50ms OR MORE
ALARM
ALARM
HIGH = ALARM
LOW = STAND-BY MODE