Detcon DM-600IS - Manual (Page 9)

DM-600IS
DM-600IS Instruction Manual Rev 1.5.9 Page 5 of 37
2.0 PRINCIPLE OF OPERATION
Method of detection is by an electrochemical reaction at the surface of an electrode called the sensing
electrode. Air and gas diffuse through the capillary diffusion barrier. The controlling circuit maintains a small
external operating voltage between the sensing and counter electrodes of the proper bias and magnitude so that
no current flows to or from the reference electrode while its potential is maintained at the correct fixed voltage
— usually ground. The electrochemical reaction creates a change in current flow from the counter electrode to
the sensing electrode. This change in current is proportional to the gas concentration and is reversible. The
quick response of the sensor results in continuous monitoring of ambient air conditions. The Intrinsically Safe
Sensor Housing design allows direct contact of the target gas to the electrochemical sensor, thus maximizing
response time, detectability and repeatability.
Figure 5 Functional Block Diagram
3.0 APPLICATION
3.1 Sensor Placement/Mounting
Sensor location should be reviewed by facility engineering and safety personnel. Area leak sources and
perimeter mounting are typically used to determine number and location of sensors. The sensors are generally
located 2 - 4 feet above grade.
3.2 Interference Data
Detcon Model DM-600IS series electrochemical sensors are subject to interference from other gases. This
interaction is shown in the table in section 3.4 as the relation between the amount of the interfering gas applied
to the sensor, and the corresponding reading that will occur. All measurements are in ppm unless otherwise
noted.
The table is laid out with the Model Number of each sensor in a column on the left side of the page. The
interfering gases are listed in a row across the top of the page. Each page lists all Model Numbers but 5 pages
are necessary to list all interfering gases, thus each page is a repeat of the full line of Detcon sensors. Be sure
to reference each page to ascertain the full listing of interfering gases for a particular sensor.
As an example, the first listing shows that the Model DM-600IS-C2H30 acetaldehyde sensor will have an
interference reading of 340 ppm if 40 ppm of C2H2 (Acetylene) is applied.
NOTE: Interference factors may differ from sensor to sensor and with life time. It is not
advisable to calibrate with interference gases. They should be used as a guide only