Model 580A
10
•
Halides (compounds containing chlorine, fluorine, bromine, or iodine).
•
Sulfur compounds such as SO
2
(Sulfur Dioxide), H
2
S (Hydrogen Sulfide), CS
2
(Carbon Disulfide).
•
Heavy metals such as tetraethyl lead.
•
Silicones (often contained in greases and aerosols). Silicones do not chemically
attack the sensor. They, instead, coat the beads and, therefore, reduce or stop
the oxidation of the combustible gas at the catalytically active bead.
•
Acid
vapors.
•
Caustic liquids or vapors.
The presence of such materials in an area does not necessarily preclude the use of a
catalytic bead sensor. The feasibility of using a sensor in such areas must be determined
by an analysis of the specific factors in each application. However, sensors used in such
areas usually require calibration checks on a more frequent basis, and typically have a
shorter life than normal. In many such applications, the normal two-year warranty does
not apply.
CAUTION:
General Monitors discourages the painting of sensor assemblies for two
reasons. First, if the sensor head is painted-over, gas will not be able to
diffuse into the sensor. Second, many paints contain lead, which can poison
a sensor.
2.6 Sensor Installation
Various types of sensors can be provided with the Model 580A Controller. However, the
installation method is identical in all cases. Please refer to Section 7.6 for further
information.
The sensor assembly, (Figure 4), is used most often. It consists of P/N 10001-1 sensor
plus GMI P/N 10252-1 Sensor Housing.
This assembly (P/N 10001-1 + P/N 10252-1) is CSA approved for NEC Class I, Division 1
and Division 2, Groups B, C and D hazardous areas.
Each sensor assembly is connected to the controller using 3-conductor stranded cable,
and must be installed with conduit in hazardous areas. Total loop-resistance excluding
the sensor must not exceed 40-Ohms. A separate cable is required for each sensor.
GMI recommends the use of shielded cable generally, though in some cases it is not an
absolute necessity. Due to the low levels of sensor signal voltages, shielded cable is
required
in some installations to guard against extraneous electrical noise. The shield
must be enclosed in a suitable insulating outer jacket, and must be grounded only at the
rear-panel sensor-shield ground terminal (Figure 4). Care must be taken to assure that
the shield does not contact the sensor housing or metal conduit.
CAUTION:
Avoid running sensor cables close to high power cables, radio transmission
lines, or cables subject to pulses of high current.
