Cold Junctions In Thermocouples - Pepperl+Fuchs LB Series Manual

LB Remote I/O System
Installation
LB2*

The valve control circuit is monitored by a current pulse. This current pulse is brief enough
not to operate a connected valve. If the I/O module is being used with indicator lights or
sounders, you can switch off the current pulse for each channel. It is not always possible
to monitor the valve circuit when booster valves are used because these valves have a
storage capacitor that behaves like a short circuit when the valve is switched off. In such
cases, depending on the valve, a 10 k parallel resistor enables line fault detection for
booster valves. If line fault detection is still detected when the valve is off, even with the
parallel resistor connected, disable the line fault detection function.
The line fault detection function of the analog I/O modules is based on a current measurement.
An additional resistor circuit is not required.
For more information, refer to the software manual for the com unit used.
3.9

Cold Junctions in Thermocouples

The I/O modules LB5*02* and LB5*05* are equipped with an internal cold junction. However,
they can be used with an external cold junction. The temperature detected by the external cold
junction at the terminal connection is used by the I/O module to compensate for the influences
of the ambient temperature.
External cold junctions are available as accessories. See chapter 2.6.2
1
Figure 3.12
1. Protective cover
2. Cold junction consisting of a terminal block and a Pt100 thermocouple on terminal open-
ings 1 and 2
If the cold junction is operated in a 2-wire configuration, the line resistance can be entered into
the configuration software to compensate for the line resistance to the external cold junction.
For more information, refer to the software manual for the com unit used.
40
2
2
1
External cold junction for thermocouple measurements