Table of Contents
Advertisement
...2 DESCRIPTION
Metering
valve
Gas
sample
inlet
When the intrinsically safe stabilized current from the 4234
power supply unit (model 4234500 or 4234501) is passed
through this bridge, the temperature of the platinum filaments
rises to a point of thermal equilibrium. Under conditions which
are arranged to give minimum radiation and convection heat
transfer, the equilibrium temperature depends on the thermal
conductivity of the gas surrounding the filament. Thus any
difference between the thermal conductivity of reference and
sample gases causes an imbalance in the bridge; this imbalance
(as a millivolt signal) is indicated by the monitor unit.
Zener diodes are connected across the input connections from
the power supply unit to the katharometer in order to limit the
maximum voltage which could be developed across the filament
bridge under external fault conditions. The current is limited to a
safe value under fault conditions by the power supply unit.
2.3 Model 4234500/4234501 Power Supply Units
(PSU) – Fig. 3.3
Warning. Do NOT connect mains supply to the
PSU with the output terminals on open circuit. This causes
premature component failure.
Caution. Ensure that the PSU is correct for the
mains supply voltage available. A nominal 115 V unit cannot
be adapted for use with a nominal 230 V supply, or the other
way around.
To operate a katharometer unit in the hazardous area, one Model
4234 PSU is required for each katharometer. The PSU supplies
a stabilized mA d.c. signal, and must be mounted in the safe
area. There are two separate versions available:
Model 4234500 for a nominal 230 V a.c. supply voltage
Model 4234501 for a nominal 115 V a.c. supply voltage
4
Katharometer
unit case
Drying chamber
Fig. 2.2 Location of Items – A Katharometer Analyser Panel
Local zero
adjustment
The stabilized current output is current and voltage limited to
restrict the energy supply into the hazardous area.
The PSU is housed in a metal case fitted with lugs for wall/panel
mounting. Cable gland entries are provided at opposite ends of
the case for supply voltage input and stabilized output cables to
the hazardous area.
The circuit is protected by a cartridge fuse. This fuse must have
a high breaking capacity (h.b.c.) rating of 1500 A to comply with
the terms of the certification.
2.4 Remote Indicator/Controllers
The 6553 monitor unit has provision for retransmission values
and ancillary indicator/controllers may be connected to these
outputs, providing that they are installed in the safe area and the
installation conforms to the requirements given in Section 5.1.
Gas sample
outlet
Electrical
interconnections
Flow gauge
Advertisement
Table of Contents
