WIKA RTD Manual De Instrucciones página 11

5. Commissioning, operation
5.1.4 Tapered threads
With NPT or other tapered threads, it should be checked whether it may be necessary
to seal them additionally with PTFE tape or hemp. The threads must be lubricated with a
suitable lubricant before fitting.
5.1.5 Mounting instructions for electrical thermometers with ceramic protection tube
Ceramic thermowell materials withstand changes in temperature only to a limited extent. A
temperature shock can therefore easily result in stress cracks and consequently in damage
to the protection tube.
For this reason, preheat thermocouples with ceramic or sapphire protection tubes before
installation, and then slowly immerse them into the hot process.
In accordance with DIN 43724, an insertion speed of 1 cm/min is recommended for protec-
tion tubes with a diameter of 24/26 mm. For smaller diameters of 10/15 mm, the speed can
be increased to 50 cm/min. As a basic principle, higher process temperatures require a
lower insertion speed.
In addition to the protection from thermal stress, ceramic protection tubes must also be
protected from mechanical loads. The reason for these harmful stresses are bending forces
in case of a horizontal mounting position. As a consequence, an additional support must
be provided in case of a horizontal mounting position depending on the diameter, greater
nominal lengths and the design.
In principle, the deflection problem also occurs for metal protection tubes, particularly
for insertion lengths > 500 mm. For process temperatures > 1,200 °C, vertical mounting
should be preferred.
5.2 Electrical mounting
Using a transmitter/digital display (option):
Observe the contents of the operating instructions for the transmitter/digital display (see
scope of delivery).
Cable glands
Requirements for meeting ingress protection:
Only use cable glands within their indicated clamping range (cable diameter suitable for
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the cable gland).
Do not use the lower clamping area with very soft cable types.
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Only use round cables (if necessary, slightly oval in cross-section).
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Do not twist the cable.
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Repeated opening/closing is possible; however only if necessary, as it might have a
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detrimental effect on the ingress protection
For cable with a pronounced cold-flow behaviour the gland must be fully tightened.
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WIKA operating instructions RTD and TC
EN
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