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11 MAINTENANCE
Warning.
• Each unit of this system forms an integral part of a
certified intrinsically safe system. Appropriate safety
precautions must be taken to prevent any incendive
electrical discharges in the hazardous area when
carrying out any of the following tasks.
• Equipment in this system operates on a.c. mains
supply voltage electricity. Suitable precautions must
be taken to avoid the possibility of electric shock.
• The maximum pressure and temperature specified for
particular parts of the system must not be exceeded.
The katharometer unit and its associated equipment are
designed for stable and accurate operation over long periods.
This section covers the requirements for fault finding,
diagnostic tests and maintenance tasks.
11.1 General Maintenance
11.1.1 Pressure
The operation of the katharometer units is not affected
significantly by changes in pressure providing that they are
within the pressure limits given in Section 13.
11.1.2 Flow
The
katharometer
zero
independent of the sample flowrate, as the sample gas
sensing system depends on molecular diffusion. But the speed
of response is affected by the flowrate. This means that the
flow resistance of the drying chamber is a compromise
between obtaining speed of response, and avoiding a rapid
degradation of the desiccant.
11.1.3 Leaks
There is an inherent safety requirement that there are no leaks
into or out of the sample system. Any leaks could also affect
the correct operation of the katharometer unit.
11.1.4 Vibration
The katharometer unit tolerates reasonable levels of
mechanically induced vibration. Pulsations due to unsteady
sample flow can affect the katharometer filaments and cause
errors due to excessive cooling.
11.1.5 Contamination
Contamination in the sample system can arise from oil or
suspended particles, or from erosion of material from the
sample system upstream of the katharometer unit.
11.1.6 Ambient Temperature
The calibration of the katharometer is not significantly affected
by variations of the ambient temperature. Temperature
changes can affect the sensitivity and reduce accuracy on
sensitive ranges.
balance
and
sensitivity
11.1.7 Bridge Current
The working current of the katharometer bridge is 350mA
supplied from the power supply unit. This value must remain
stable during normal operation as the katharometer output signal
is approximately proportional to the cube of the bridge current.
11.2 Diagnostic Tests
11.2.1 Checking Output of 4234 Power Supply Unit
Carry out the test procedure given in Section 6.3.1.
11.2.2 Checking Integrity of Zener Barrier Units
Carry out the test procedure given in Section 6.3.2.
11.2.3 Checking the Katharometer Output
Warning.
• This unit is part of the certified intrinsically safe system.
Appropriate safety precautions must be taken to prevent
any incendive electrical discharges in the hazardous
area when carrying out this task.
• Ensure that the proper electrical safety precautions are
taken at all times when undertaking this procedure.
1) Electrically isolate the monitor unit
2) Remove the outer cover from the 6548 001 katharometer unit.
3) With the katharometer operating, check if the voltage across
are
terminals TB1 - 1 and TB1 - 4 is not above 4V with 350mA
passing. If the voltage is above this value it is likely that one or
more filaments of the bridge is broken.
4) With the katharometer operating, check that the voltage
across terminals TB1 - 1 and TB1 - 4 is below 2.8V with
350mA passing. If the voltage is below this value and there is
no zero adjustment available, it is likely that there is an
accumulation of liquid within the katharometer block.
5) If the reading from the test made at step 3 is unstable when
the katharometer block is tapped gently, this could indicate
that a filament is damaged but not open circuit.
If any of these tests indicate that the katharometer is faulty the
complete katharometer unit must be returned for repair or
replacement.
The span adjustment of katharometer units are sealed and must
not be tampered with.
33
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