Servodrives / inverters series COSMOS 301X Installation, use and maintenance manual - EN
5.7.17 Thermocouple J input
Some versions of servo-drives/inverters are equipped with an input for reading type-J thermocouples; they
are commonly used for temperature detection in several industrial applications. Since these sensors deliver a
voltage signal depending on the different temperature of the hot joint and of the cold joint, it is necessary to
measure the cold joint temperature by means of a different device, in order to obtain the absolute
temperature of the hot joint (that is to say the sensor). The servo-drive integrates an electronic temperature
sensor, that is to say it compensates the cold joint temperature automatically. Since the sensors are
polarized, be careful to the polarity during the wiring.
Thermocouples of different types are made of different alloys; therefore, the use of different thermocouples
would imply a wrong detection. If the thermocouple cable should not be long enough, use the provided
extension cables, made of the same material as of the thermocouple. Also the junctions must be made with
the provided polarized connectors.
The thermocouples can be insulated or not insulated; in the latter case, the junction is electrically connected
to the sheath. Since the acquisition stage is of non-insulated type, it is strictly recommended to use insulated
thermocouples; otherwise, eddy currents may generate, due to imperfect equipotentiality between the
thermocouple and the servo-drive, with consequent errors of measurement.
The recommended connection scheme, including extension cable, is shown in the following picture.
Since the amplitude of the signals delivered by the thermocouple is very low, the signals are particularly
susceptible to electrical interference. For this reason, above all when the wiring extends over great
distances, it is strictly recommended to use a shielded cable. If an extension cable is used, it is necessary to
join the thermocouple shield and the extension cable (see picture).
Ver. 1.09 SMITECdd 58/74
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