35-3010A-11 Sample-Draw Detector • 9
Flow Block
The flow block is located in the lower right corner of the sample draw detector. All the
sensors are installed in the flow block. The flow block routes the sampled air to each
sensor.
EXHAUST Fitting
The EXHAUST fitting on the bottom of the housing allows the gas sample to exit the
sample draw detector. The EXHAUST fitting accepts 1/4 in. rigid tubing. See
“Installation” on page 13 for instructions to connect tubing to the EXHAUST fitting.
Detection System
The detection system consists of the LEL, H
2
S, and CO
2
sensors, preamp circuit board,
and the main circuit board.
Combustible Gas Sensor
The combustible gas sensor is installed in the lower left of the flow block. The combustible
gas sensor includes the sensing elements, flame arrestor, connector, and sensor leads.
Sensing Elements
Two sensing elements are protected within the sensor assembly. Through a series of
thermal and electronic reactions, these elements produce an output that is proportional to
the detection range of the sample draw detector. The signal from the sensor is sent to a
controller.
The porous flame arrestor allows the gas sample to enter the sensor assembly and contact
the sensing element. The flame arrestor also contains sparks within the sensor.
Connector
The top of the sensor includes five pins that plug into the socket connector. This connector
allows you to replace the sensor without disconnecting the wiring. The sensor leads are
soldered to the connector.
Sensor Leads
Four color-coded leads extend from the connector. The leads allow you to connect the
combustible gas sensor to the main circuit board.
CO Dummy Plug
The CO sensor position in the flow block is occupied by a plastic dummy plug in the
35-3010A-11.
Hydrogen Sulfide Gas Sensor
The hydrogen sulfide gas sensor is installed in the upper right side of the flow block. It
has 4 pins which mate with sockets on the preamp circuit board.
Carbon Dioxide Sensor
The infrared carbon dioxide sensor is installed in the smaller flow block. A small circuit
board with a cable mates to it and retains it in the block. The cable is wired to the main
PCB.
