Rockwell Automation 1790-XXXX CompactBlock LDX I/O DeviceNet RTD and Thermocouple - Manual (Page 10)

10
Publication 1790-IN011B-EN-P - April 2003
When using a 3-wire configuration, the block
compensates for resistance error due to lead wire length.
For example, in a 3-wire configuration, the block reads
the resistance due to the length of the wires and assumes
that the resistance of the other wire is equal. If the
resistance of the individual lead wires are much
different, an error may exist. The closer the resistance
values are to each other, the greater the amount of error
is eliminated.
IMPORTANT
The RTD block requires three wires to
compensate for lead resistance error. We
recommend that you do not use 2-wire
RTDs if long cable runs are required, as it
reduces the accuracy of the system.
However, if a 2-wire configuration is
required, reduce the effect of the lead
wire resistance by using a lower-gauge
wire for the cable (for example, use AWG
#16 instead of AWG #24). The block’s
terminal strip accepts AWG #14 gauge
wire.
IMPORTANT
To ensure temperature or resistance value
accuracy, the resistance difference of the
cable lead wires must be equal to or less
than 0.01 ohm.