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Start Delay
When power is first applied to the monitor it will initiate a 90 second warm-up routine. During this time it will
output 3.0mA and the Status LED will flash (slow) red. After warm-up, the monitor will enter the normal
operation (clear) mode, the analog output will change to 4.0mA and the Status LED will blip green.
Sensor Fault
CAUTION
The fault detection circuitry does not monitor the operation of external response equipment or the
external wiring to these devices. It is important that these devices be checked periodically to ensure
they are operational.
The microcontroller-based Toxic Detector features self-testing circuitry that continuously checks for
problems that could prevent proper response. When power is applied, the microcontroller automatically
tests the system to ensure that it is functioning properly. During normal operation, it continuously
monitors the signal from the internal sensor source. In addition, a "watchdog" timer is maintained to
ensure the program is running correctly.
When a system fault is detected, the Status LED flashes (fast) red, the LED alphanumeric display shows
“Sensor Fault” and the fault relay changes state.
Sensor Drift
It is a normal characteristic of gas sensors to exhibit a slow drift from zero. When the amount of drift exceeds
10% since the last calibration, the analog output switches to a value of 2.5mA, the status LED flashes red and
the NEG DRIFT message scrolls on the display until manually reset and the system is re-calibrated. When the
analog output switches to 2.5mA due to drift, the sensor will still respond and transmit reasonable analog
output signals if gas is present.
Normal
With no gas present and no fault detected “Normal” will be illuminated on the alphanumeric LED display to
indicate a clean air status, Status LED will blip green and the analog output is 4.0 mA.
Hardware
Cal/Reset
A pushbutton for programming, zeroing, and resetting the Toxic Detector is provided. Depressing this
push button for less than one second will initiate a basic system reset (clear a latched gas alarm).
Programming the Toxic Detector is accomplished by depressing the push button for greater than one
second.