Hardware, Start Delay, Sensor Fault, Normal

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.