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DESCRIPTION

2.2

Model 006540203 or 006548000

Katharometer Analyzer Panel – Fig. 2.2

Refer also to IM/6517-6518 for further details.
Each panel comprises a metering valve, a drying chamber, a
thermally lagged katharometer (Model 006539 or 006548) and a
flowmeter. These items are mounted on a flat panel suitable for
fixing to a vertical surface close to the sample point. The
katharometers are calibrated for the hydrogen purity
measurement as well as hydrogen in purge gas* and air in purge
gas*.

Each katharometer assembly incorporates a Wheatstone Bridge
comprising fine, glass-coated platinum filaments. One pair of
parallel arms is sealed in the reference gas and the other pair
exposed to the sample gas.

When the intrinsically safe stabilized current from the 4234
power supply unit (Model 4234 500 or 4234 501) is passed
through this bridge, the temperature of the platinum filaments
rises to a point of thermal equilibrium. Under conditions that 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 display.

Zener diodes are connected across the input connections from
the power supply unit to the katharometer in order to limit the
maximum voltage that could be developed across the filament
bridge under external fault conditions. Under fault conditions the
current is limited to a safe value by the power supply unit.

2.3

Model 4234 500/4234 501

Power Supply Units (PSU) – Fig. 3.3

Refer also to IM/4234500 for further details.

Caution

. Do not connect the mains supply to the PSU

with the output terminals open circuit.

Caution

. Ensure that the PSU is correct for the mains

supply voltage available. A nominal 115V unit cannot be
adapted for use with a nominal 230V supply, or vice
versa.

To operate a katharometer unit in the hazardous area, one Model
4234 PSU is required for each katharometer. The PSU supplies
a stabilized DC current output and

must

be mounted in the

safe

area. There are two versions available:

Model 4234 500 for a nominal 230V AC supply voltage
Model 4234 501 for a nominal 115V AC supply voltage

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 current output
cables to the hazardous area.

The circuit is protected by cartridge fuses. The fuses (F2 and F3)

must

have a high breaking capacity (HBC) rating of 1500A to

comply with the terms of the certification.

2.4

Remote Indicator/Controllers

The 6553 Display Unit has retransmission outputs for
connection to indicator/controllers, providing that they are
installed in the

safe

area and the installation conforms to the

requirements given in Section 5.1.

Fig. 2.2 Location of Items – Model 6540 203 and 6548 000 Katharometer Analyzer Panels

Terminal box to connect low flow
sensor to low flow alarms