Det-Tronics PW9200x Pathwatch IR Gas Detection System - Manual (Page 6)

Threshold Detector:
Hydrocarbon Vapor Alarm Relay
The threshold detector activates when the RATIO volt-
age increases above a preset value. Activation of the
threshold detector causes the vapor alarm relay to
energize. The threshold level at which the hydrocar-
bon vapor alarm relay is energized can be adjusted
and tested on the front panel.
Threshold Detector:
Obstruction/Instrument Status Alarm Relay
The threshold detector activates when the NUMERA-
TOR (reference) voltage approaches zero. When the
threshold detector activates, the obstruction/instru-
ment status alarm relay to de-energizes. Because the
relay is energized in normal operation and is de-ener-
gized when the beam is blocked or when an instru-
ment malfunction occurs, the alarm is fail-safe.
Section 2
Operation
SAFETY INFORMATION
EXPLOSION-PROOF INTEGRITY
WARNING
The PW9200 housings or associated junction
boxes must never be opened when circuits are
alive and hazardous vapor conditions may exist.
Ensure that no hazardous vapor conditions exist
in procedures where the cover, window assem-
bly or junction box is to be opened when circuits
are alive.
CAUTION
If power is to be disconnected for an extended
period, e.g. over one week, the instrument
should be removed to a protected environment.
Special precautions must be taken with the PW9200
to ensure the integrity of the explosion-proof hous-
ings. When the instrument is in operation, the window
assemblies must be securely tightened. The cover
bolts must be torqued to 20 foot pounds.
Scratches may affect the strength of the instrument
windows, so care must be taken to avoid scratching
them during installation, operation and servicing.
Similarly, the mating surfaces of the cover and the
housing flange should not be scratched and these
surfaces should be protected during servicing.
The light beam projected by the PW9200 transmitter
could cause combustible materials within its path to
ignite or raise the temperature of an object within its
path above the self-ignition temperature of some
gases. Check the temperature code for the transmit-
ter wattage used (see instrument nameplate) and do
not install the instrument at any location where this
dangerous condition could occur.
PERSONNEL SAFETY
The American Conference of Governmental Industrial
Hygienists (ACGIH) has established threshold limit
values (TLVs) or maximum allowable exposures to
bright light sources during an eight hour workday.
According to ACGIH, “these values are to be used as
guides to the control of exposure to light and should
not be regarded as the fine line between safe and
dangerous levels”.
WARNING
It is possible to exceed the ACGIH limit values by
viewing the instrument’s light source directly from
the center of the light beam at distances less
than approximately ten feet from the source. DO
NOT stare directly into the light source at close
range.
As with the sun, which greatly exceeds the Threshold
Limit Values established by the ACGIH, the eye’s self-
protection mechanism (blinking) activates and auto-
matically prevents overexposure. However, close
range viewing of the transmitter beam must be avoid-
ed.
FRONT PANEL CONTROLS
Front panel controls are described in the following
paragraphs and are illustrated in Figure 2. Access to
the front panel controls is gained by removing the
receiver window assembly.
OUTPUT ZERO POTENTIOMETER
The ZERO adjustment potentiometer is used to set the
analog output (RATIO) to zero volts when the instru-
ment views hydrocarbon-free air.
MODE SWITCH
The MODE selector switch permits adjustment of the
instrument’s response time and testing of the alarm
circuits.
4