Manual

4
3.1 95-8631
CERTIFICATION—
For complete approval details for the PIRVOLLT Process
Gas Monitor and the PointWatch Termination Box Model
PIRTB, refer to the appropriate Appendix:
Appendix A - CSA
Appendix B - ATEX/CE
Appendix C - IECEx
WARNING
Always ensure that the detector/termination
box hazardous (classified) location ratings are
applicable for the intended use.
DESCRIPTION
DETECTION METHOD
PIRVOLLT operates on the infrared absorption
principle. A beam of modulated light is projected
from an internal infrared source to a reflector, which
sends it back to a pair of infrared sensors. One of the
sensors is designated reference and the other active,
with different optical filters in front of the two sensors to
make them selective to different infrared wavelengths.
The reference wavelength is unaffected by combustible
gases, while the active wavelength is absorbed by
combustible gases. The ratio of the active to the
reference wavelength is computed within the PIRVOLLT
to determine the concentration of gas present. This
value is then converted into a 4 to 20 mA current output
for connection to external display and control systems.
CURRENT LOOP OUTPUT
During normal operation, the PIRVOLLT has a 4 to 20 mA
current output that is proportional to gas concentrations
from 0 to 100% by volume methane. A current output less
than 4 mA indicates a fault condition (see Table 1).
SIGNAL DISPLAY DEVICE
If a local or remote digital display for indication of detected
gas concentration is required, it is recommended to utilize
a scalable display device with a clearly marked unit of
measurement in % by volume. Under no circumstances
should a % LFL unit of measure display module be used
to display the PIRVOLLT signal output.
OPERATING MODES
Warmup
When power is applied to the PIRVOLLT, it enters a
Warmup mode (for approximately one minute) in which
it performs diagnostic checks and allows the sensors
to stabilize before beginning normal operation. The
current output during this period is 0 mA. At the end of
the warmup period with no faults present, the PIRVOLLT
automatically enters the Normal operating mode. If a
fault is present after the warmup, the current output will
indicate a fault.
Normal
In the normal operating mode, the 4 to 20 mA signal
level corresponds to the detected gas concentration.
The PIRVOLLT continuously checks for system faults or
initiation of calibration, and automatically changes to the
appropriate mode.
Fault
Faults detected during warmup, normal operation, or
calibration are indicated by the current loop output as
shown in Table 1.
Calibration
The PIRVOLLT is calibrated at the factory for detection of
methane. No field calibration is required under normal
circumstances.
In the event the PIRVOLLT optics are fouled and complete
optics disassembly for cleaning is required, device re-
zeroing may be required after re-assembly. Refer to the
“Calibration” section for details.
NOTE
A momentary connection of the calibration lead
wire to DC negative (common) of the power
supply initiates the zero and span calibration
sequence. When wiring the PIRVOLLT, use care
to isolate it from accidental contact with the PIRTB
and/or other conductors.
FM
APPROVED
®
FM
APPROVED
®