Answer / vinoth

In RTD, we are measuring temperature through Resistance
change. Normally we are measuring this parameter in the
field. while transmitting, these signal to control panel
through cable, some additional resistance due to distance
will add upto the RTD resistance value. which shows
incorrect value. in order to overcome these, normally in 2
wire system, we will manual add/subtract some resistance
value with the measured resistance value.but it is no percise
whereas in 3 wire system, a parallely third wire run with
the two polarity wires, but its direction of current flow is
opposite to the other two. so it will cancel the line
resistance and give exact value. similarly, for more precise
and accurate measurement, we mostly use 4 wire system.
In above mentioned description, the addition of resistance
or removal of line resistance through extra wire is called
compensation for RTD

Answer / sandip patel

RTD means resistor temperature detector .its resistance is increase with increasing of the temperature. 2wire RTD is used for direct use of it but 4 wire RTD used when the compansation is needed in plant for removing the errors.

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Sir,I am going to sit for IOCL written test exam. recently.Can anyone tell me the name of 'Objective type Question Book on Instrumentation Engineering ' which will help me. Pl. mail to bidyut_71@rediffmail.com / bidyut.saha2008@indiatimes.com / bidyut.saha09@yahoo.in

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