Cold Junction Compensation Setting Function - Mitsubishi Electric MELSEC iQ-R Series User Manual

1.8

Cold Junction Compensation Setting Function

This function enables two types of cold junction compensation (using a cold junction compensation resistor or an external
method (cooling bath)) by setting whether to use a cold junction compensation resistor. Only the thermocouple input module
can use the function.
Operation
The operations of cold junction compensation using a cold junction compensation resistor or using an external method are
described below.
■Cold junction compensation using a cold junction compensation resistor
Cold junction compensation using a cold junction compensation resistor is automatically executed by setting With cold
junction compensation (0) in 'Cold junction compensation with/without setting' (Un\G298).
Connect provided cold junction compensation resistor (RTD) to the relay terminal block as shown below.
Thermocouple input module
Relay terminal block
RTD
■Cold junction compensation using an external method
Set Without cold junction compensation (other than 0) in 'Cold junction compensation with/without setting' (Un\G298), and
externally install a cooling bath (high-precision). Because the thermoelectromotive force generated at reference junction of
the thermocouple conducts to the thermocouple input module without change, the cold junction compensation accuracy is
improved. Use this type of compensation to perform highly accurate temperature measurement where an error generated by
the compensation using a cold junction compensation resistor (RTD) is not allowed.
Wire the module as shown below. Note that the connection of the cold junction compensation resistor (RTD) to the relay
terminal block is not required.
Thermocouple input module
Relay terminal block
The cooling bath has a structure where a thermocouple and a conducting wire is connected inside the bath
which temperature is controlled to be 0. Therefore, the thermoelectromotive force generated by the
thermocouple at the contact site of the thermocouple and the conducting wire becomes 0V. This prevents
unnecessary thermoelectromotive force that causes an error.
Compensation lead wire
Compensation
Conducting wire
lead wire
Cooling bath
Temperature measurement object
Thermocouple
Temperature measurement object
Thermocouple
1.8 Cold Junction Compensation Setting Function
1
1 FUNCTIONS
37