8
Connecting Your Display (continued)
Connect an RTD temperature signal
to the transmitter as explained below, and run the
4-20 mA output of the transmitter trom P4-2 and P4-1 through an available gland.
t.
In 2-wire hookup,
the meter senses the com-
bined voltage drop across the RTD and both lead
wires. The voltage drop across the lead wires can
be measured by shorting out the RTD during meter
setup, and this voltage is then automatic-ally
subtracted from the combined total. However,
changing resistance of the lead wires due to
ambient temperature changes will not be com-
pensated.
In 3-wire hookup,
the meter senses the com-
bined voltage drop across the RTD plus two
excitation leads. It also senses the voltage drop
across one excitation lead, and then subtracts twice
this voltage from the combined total. This technique
effectively subtracts all lead resistance and
compensates for ambient temperature changes if
the two excitation leads are identical.
In 4-wire hookup,
different pairs of leads are used
to apply the excitation current and sense
the voltage drop across the RTD for ratiometric
operation, so that the IR drop across the excitation
leads is not a factor.
For more informatiin on Laureate thermocouple transmitters, see https://www.laurels.com/
transmitter-thermocouple.php and the user manual at https://www.laurels.com/downloadfiles/
LT-manual-analog-in.pdf
