Beckhoff EL33-00 Series, Документация

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Commissioning
EL33xx-00x0 154 Version: 4.2
5.7 Operation with an external cold junction
For temperature measurement with an external reference point/cold junction, the value "2" (external process
data) must be set in object
0x80n0:0C [ } 157] . The thermocouple is not connected directly to the terminal in
this case (the cold junction compensation would take place internally in the case of direct connection), but
rather it is coupled to the terminal via a connecting cable.
In this case, the temperature T
v
is sensed by a temperature sensor at the cold junction and fed to the
process via the fieldbus master and fieldbus as a variable ("external") (see fig. External cold junction ). The
reference data are written into index 0x70n0:11 [
}
160] .
Alternative to cold junction measurement
As an alternative to the procedure described above, the cold junction can be maintained at a de-
fined temperature through ice water (0° C), for example. In this case, the temperature is known
without measurement of the cold junction temperature (Fig.
External cold junction ) and can be re-
ported to the EL33xx via the process data.
EL3314-0002, EL3314-0010
The EL3314-0002 since FW01 and the EL3314-0010 since FW03 does also support the external
reference point measurement. The user have to ensure, that an application of external cold junction
measurement have no negative effect to the measurement accuracy.
Fig. 173: External cold junction