Why use 3 wire RTD insted of 2 wire or 4 wire

IT IS DEPENDENS ON ACCURACY AND PROCESS REQUIREMENTS.THREE WIRE AND FOUR WIRE ARE USED FOR MORE ACCURACY THEN TWO WIRE.FOUR WIRE USED IN LABORATORIES MOSTLY.

MOST RTD’S INCORPORATE A THIRD WIRE WITH RESISTANCE R3.THIS
CONFIGURATION PROVIDES ONE CONNECTION TO ONE END AND TWO TO
THE OTHER END OF THE SENSOR. CONNECTED TO AN INSTRUMENT
DESIGNED TO ACCEPT 3-WIRE INPUT, COMPENSATION IS ACHIEVED
FOR LEAD RESISTANCE AND TEMPERATURE CHANGE IN LEAD
RESISTANCE. THIS IS THE MOST COMMONLY USED CONFIGURATION.
IF THREE IDENTICAL TYPE WIRES ARE USED AND THEIR LENGTHS ARE
EQUAL, THEN R1 = R2 = R3. BY MEASURING THE RESISTANCE
THROUGH LEADS 1, 2 AND THE RESISTANCE ELEMENT, A TOTAL
SYSTEM RESISTANCE IS MEASURED (R1 + R2 + RE ). IF THE
RESISTANCE IS ALSO MEASURED THROUGH LEADS 2 AND 3 (R2 + R3),
WE OBTAIN THE RESISTANCE OF JUST THE LEAD WIRES, AND SINCE
ALL LEAD WIRE RESISTANCES ARE EQUAL, SUBTRACTING THIS VALUE
(R2 + R3) FROM THE TOTAL SYSTEM RESISTANCE (R1 + R2 + RE)
LEAVES US WITH JUST RE, AND AN ACCURATE TEMPERATURE
MEASUREMENT HAS BEEN MADE.

A 4-WIRE CONFIGURATION IS ALSO USED. TWO CONNECTIONS ARE
PROVIDED TO EACH END OF THE SENSOR. THIS CONSTRUCTION IS
USED FOR MEASUREMENTS OF THE HIGHEST PRECISION.WITH THE
4-WIRE CONFIGURATION, THE INSTRUMENT WILL PASS A CONSTANT
CURRENT (I) THROUGH THE OUTER LEADS, 1 AND 4.

ABOVE 200 M DISTANCES WE HAVE TO USE 3 WIRE FOR COMPENSETION
THE RESISTANE LOSSES IN THE RTD CABLE

AND VERY LONG DISTANCE WE HAVE TO USE 4 WIRE FOR
COMPENSETION THE RESISTANE LOSSES IN THE RTD CABLE

ANY PROBLEM PLS REVERT.

shail2110

hello expert

please said why use 3 wire RTD instead of 2 wire or 4 wire

what is exact reason for choosen

thanks

shailesh

So Its Depend on you and your application...