Detcon DM-700 - Manual (Page 5)

Model DM-700
DM-700 Instruction Manual Rev. 4.0 Page 1 of 48
1. Introduction
1.1 Description
Detcon Model DM-700 toxic gas and O
2
deficiency sensors are non-intrusive
“Smart” sensors designed to detect and monitor a wide range of toxic gasses in air.
Ranges of detection for toxic gasses are from 0-1ppm up to 0-10,000ppm. Ranges
for O
2
deficiency are 0-100ppm up to 0-25% by volume. The sensor features an
LED display of current reading, fault and calibration status. The Sensor is
equipped with standard analog 4-20mA and Modbus™ RS-485 outputs. A primary
feature of the sensor is its method of automatic calibration, which guides the user
through each step via fully scripted instructions displayed on the LED display.
The microprocessor-supervised electronics are packaged in an encapsulated module
and housed in an explosion proof casting, called the ITM (Intelligent Transmitter
Module). The ITM includes a four character alpha/numeric LED used to display
sensor readings, and the sensor’s menu driven features when the hand-held
programming magnet is used.
Electrochemical Sensor Technology
The Toxic gas sensors are based on electrochemical cells. Each cell consists of three electrodes embedded in
an electrolyte solution all housed beneath a diffusion membrane.
Sensitivity to specific target gasses is
achieved by varying composition of any combination of the sensor components. Good specificity is achieved
in each sensor type. The cells are diffusion limited via small capillary barriers resulting in a long service life
of up to three or more years. The electrochemical cell is packaged as a field replaceable intelligent plug-in
sensor.
Figure 1 Construction of Electrochemical Toxic Sensor
The O
2
deficiency sensor technology is a two electrode galvanic metal air battery type cell, which is housed as
a field replaceable intelligent plug–in sensor. The cell is diffusion limited and functions as a direct current
generator proportional to the amount of oxygen adsorption. The sensors are temperature compensated and
show good accuracy and stability over the operating temperature range of –20° to 50°C (-4° to +122°
Fahrenheit). The sensor is warranted for two years and has an expected service life of up to 2.5 years in
ambient air at 20.9% oxygen.