Model 580A
9
2.4 Remote Reset Connection
Remote Reset (of alarm circuits) connections are made to rear panel terminal board
connections
RESET
and the
24VDC (-)
terminal. If a remote reset switch is used, it must
be a “
normally open, momentary action
” type.
NOTE:
If the system is to be powered from a primary DC power supply or if battery
backup is provided, the
24VDC (-)
terminal has two wires when remote reset is
used. The diameter of the two wires cannot be larger than an AWG 14 wire.
2.5 Choosing Sensor Locations
Several variables are involved in selecting locations to install sensors. There are no hard
and fast rules defining the optimum location. However, the following general suggestions
should be considered with regard to particular conditions at the site where a Model 580A
Controller is being installed.
2.5.1 Vapor
Density
Whether the gas/vapor to be monitored is lighter or heavier than air affects sensor
placement. For lighter-than-air gases, sensors are generally placed close to the roof or
ceiling in indoor installations. For gases much heavier than air, sensors are generally
placed near the floor or ground when there are no air currents in the area. Gases with a
density equal to air or slightly greater than air tend to rise, particularly when air currents
are present.
2.5.2 Air
Currents
If there are winds, fans, or other sources of air movement, combustible gases tend to rise
or to accumulate in certain sections of a facility. Local air currents should be studied to
aid in selection of sensor locations.
2.5.3 Likely Sources of Gas Emission
In general, at least one sensor should be located in close proximity to each point where a
leak of a combustible gas is likely to occur. This is particularly important when a liquid
having a high volatility is to be monitored.
2.5.4 Environmental Factors
Avoid installing sensors where they are exposed to wind, dust, water, shock, or vibration.
Observe the temperature range limitations of sensors (Section 7.4.2).
2.5.5 Catalytic
“Poisons”
Sensors are adversely affected by prolonged exposure to certain materials. Loss of
sensitivity (i.e. reduced response to combustible gases) or corrosion may be gradual if
such materials are present in low concentrations, or it may be rapid at high
concentrations. The more important materials adversely affecting sensors are:
