Notes for the Selection and Installation of Thermometers

For your Guidance

These notes have been prepared to assist in the selection and installation
of thermometers for the purposes of ensuring as far as possible that they
give satisfactory service on the application for which they are intended
and to ensure the highest possible level of safety.

1.         Materials

1.1        Standard brass bulbs and pockets are suitable for air, oil, water and
other non-corrosive fluids.

1.2        For corrosive fluids, alternative materials e.g. Stainless Steel, Monel,
Hastelloy etc. should be specified and as a general guide, the materials
used for the process pipework/valves/tanks etc., are normally
satisfactory for the application.

1.3        Environmental conditions should be taken into account when considering
suitable materials for cases, capillary etc.

2.         Maximum Working Temperature

2.1        It is recommended that the maximum working temperature does not
exceed 60% of the full scale reading.

3.         Ambient Temperature

3.1        Instruments are designed to operate in ambient temperatures of
-20 to +60 deg C. The instruments head and capillary should be
protected from localized heat or cold sources as this can lead to
indicating errors.

4.         Installation

4.1        Care must be taken to ensure the bulb is not damaged during installation. 

Do not attempt to bend the bulb.

4.2        The sensing bulb should be totally immersed in the medium which is
being measured.  If a thermowell is being used, the heat transfer
delay can be improved by filling the thermowell with a heat transfer
substance (i.e. graphite).

4.3        When fitting bulb into thermowell it is essential that the bulb is not
forced against the bottom of the thermowell when tightening the nut.
  This can lead to an increase in pressure within the bulb and cause
incorrect readings.  The bulb should be inserted into the thermowell
until it bottoms and then withdrawn approximately 5mm before tightening
compression nut to hand tight plus quarter turn.

4.4        Check capillary is the correct length by laying along proposed route. 
Never attempt to stretch the capillary as this will lead to fracture of the system.

4.5        The capillary should be securely clipped to a wall or other solid surface
and must be free from buckling and twists and have minimum bending
radius of 60mm. Particular care should be taken at the points where
the capillary enters the case and the bulb.  Excess capillary should be
coiled and arranged in free swinging loops between the last fixing
point and the bulb.

4.6        Do not tighten instruments into the system by grasping the case as any
distortion created will lead to calibration errors.

4.7        Instrument head should be mounted in the vertical position
unless agreed with the manufacturer.

5.         Vibration, Temperature Surges & Excess Temperature

5.1        All these factors can create stress in the temperature responsive element
and can lead to fatigue, loss of accuracy and reduce life span. The manufacturer
should be consulted where these conditions are present.

6.         Threads and Jointing

6.1        All connections should be leak tight and should be tested when
first applying pressure/temperature.

6.2        Recommended maximum pressure for each size of thread and type of material
must not be exceeded.

6.3        Care must be taken to ensure mis-match of threads does not occur.

6.4        Connections with parallel threads must have the seal made on the flat seating
using a washer of material compatible with the medium.

6.5        Connections with tapered threads have the joint made by mating the threads.
It is common practice to apply jointing material to the male thread. This must be
compatible with the medium and applied in the correct quantity to ensure
non-interference with the mating of the threads.

6.6        The joint must be made by tightening the connection by means of a spanner
on the hexagon or square provided.  Do not tighten by grasping the case of the
instrument.

7.         Maintenance

7.1        The function of the thermometer does not require any special maintenance
procedures but frequent checks must be made to ensure the instrument is still
working correctly and accurately.

7.2        Failure of the temperature responsive system is often (but not always)
preceded by temperature readings becoming increasingly higher or lower that
the value of the temperature being measured. Any shift in temperature readings
greater than twice the tolerance of the instruments must be investigated and
the immediate replacement of the thermometer if it is faulty.

8.         Repairs and Spare Parts

8.1        The repair and recalibration of thermometers should be undertaken only
by competent personnel who have at their disposal the necessary facilities.

8.2        We do not recommend the carrying of spare parts but advise the carrying
of complete instruments which will allow quick replacement and ensure the system
continues to operate within the requirements of the law.

8.3        Where the cost is justified, thermometers should be returned to the manufacturer
for any remedial work.

9.         Storage

9.1        Thermometers should be stored in dry, clean conditions and care should be taken
to ensure the ambient temperature does not exceed or fall below the measuring
range of the thermometer.

9.2        They must be protected against any impact damage.

9.3        Although care is taken in packing the thermometer it is possible they can sustain
damage during transport and should be checked for damage before use.

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