Teledyne 1220 - Multipoint flammable gas and vapor detection system - Manual (Page 13)

2-3
Multi-Channel Combustible Monitor Operational Theory 2
Teledyne Analytical Instruments
2.4 Channel Module
The Model 1220 Combustible Gas Analyzer uses an Intel Microcon-
troller with on-board RAM and ROM to control all signal processing,
input/output, and display functions for the analyzer. The channel power is
supplied from two separate universal power supply modules (100-240
VAC), designed to be compatible with most international power sources.
The first power supply (triple outputs) supplies the voltages for logic
devices. The second power supply (dual outputs) supplies voltage for the
detector(s).
The power supply for the detector is provided with a stable current of
300mA.
Each detector is connected in a bridge circuit with the output signal
feeding an operational amplifier.
A block diagram of the functional relationships of the Channel Module is
shown in Figure 2-3.
2.5 Combustible Sensors
The basic elements of the combustible gas detector are shown in
Figure 2-1. The two beads each consist of a small coil of wire coated with
an appropriate material. The measuring bead coating is a mixture of a
catalytic material with an inert binder. This catalytic material is selected to
enhance the oxidation of combustible gases. The reference bead coating is
an inert material having similar thermal properties to the other bead.
REFERENCE
BEAD MEASURING
BEAD
BLACK
REFERENCE
WHITE
COMMON
RED
MEASURING
Figure 2-1 Combustible Gas Detector