THEORY OF OPERATION
6 - 2
sample air into the sensor manifold and then distributed it to
all sensors.
A single chip microcomputer is used to control the
operation of the alarm buzzer, LED, pump and light sensor.
It measures the sensor readings and calculates the gas
concentrations based on calibration to known standard gases.
The data is stored in non-volatile memory so that it can be
sent to a PC for record keeping. RS-232 transceivers
provide a serial interface between the monitor and the serial
port of a PC. A 2-line by 16-character LCD display is used
to show the readings. The user interacts with the monitor
through three keys on the front panel keypad.
The monitor is powered by a rechargeable NiMH battery or
an alkaline pack, for portability.
NOTE: The printed circuit board of the monitor is
connected to the battery pack even if the power is
turned off. Therefore, it is very important to disconnect
the battery pack before servicing or replacing sensors
or any components inside the monitor. Severe damage
to the printed circuit board may occur if the battery
pack is not disconnected before servicing the unit.