General
The cables have to be chosen that they are appropriate for the corresponding environment that means resistant against thermal, mechanical and chemical influences. All cable connections have to be well done. Measuring cables shall be laid separately and > 0.5 m away from supply cables and cross the latter rectangular. All measuring circuits shall be operated ungrounded; if necessary a one point grounding is recommended. In order to avoid electrostatic or magnetic interference the cables shall be screened respectively have twisted cores.
Valid standards and prescriptions have to be taken into account.
Cables for resistance thermometers
Between thermometer and measuring device copper cables have to be laid. In order to keep cable resistances and their temperature dependent fluctuations as small as possible, an appropriate cable section has to be chosen. Resistance thermometers can have a 2-, 3-, or 4- wire circuit depending on the requirements on accuracy. The 2-wire circuit causes the highest measuring fault. For the 2- and 3- wire circuit the so called line balancing is recommended, if the topped instruments are appropriate; thus feeding faults can be reduced or almost completely suppressed.
Cables for thermocouples
Between thermometer and measuring device the correct compensating or extension cable suitable for the thermocouple has to be laid and connected in correct polarity. The colour code of the compensating or extension cable corresponds to the applied standard for the thermocouples. All connection points are bare metal and shall be free of intermittent contacts so that they have negligible transition resistances.