Answer / imran aslam

3rd wire is used as compension and if we use 4 wire RTD it
elemeneted more resistence as compere to 3 wire.4 wire is
more perfect

Answer / all

3 wire rtd sensor have a 1 postive(red) and 2
negative(white).whenever 3 wire rtd used for long distance
that means 10 meter wire..that time wire resistance also
increased.(r=pl/a).in 4 wire rtd sensor have a 2
postive(red) and 2 negative(white).4 wire rtd used for long
distance that time the red and red wire have short.so the
resistance variation is equal.

Answer / ravikant

Lead-wire resistance in two-wire measurements causes
potentially large temperature measurement errors.

Other types of resistance measurements include three-wire
and four-wire resistance measurements. Four-wire
measurements are preferred in temperature applications
because they eliminate lead wire resistance from the
measurement.

Answer / sam.r

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.

The voltage drop is measured across the inner leads, 2 and
3. So from V = IR we learn the resistance of the element
alone, with no effect from the lead wire resistance. This
offers an advantage over 3-wire configurations only if
dissimilar lead wires are used, and this is rarely the case.

Still another configuration, now rare, is a standard 2-wire
configuration with a closed loop of wire alongside (Figure
5). This functions the same as the 3-wire configuration, but
uses an extra wire to do so. A separate pair of wires is
provided as a loop to provide compensation for lead
resistance and ambient changes in lead resistance.

Answer / saravanan

In RTD 2-wire - lead wire resistance can drastically reduce
the accuracy of the measurement by adding additional,
uncompensated resistance into your system.

In RTD 2-wire - Third wire to help the circuit compensate
for lead wire resistance and thus provide a truer indication
of the measured temperature.

In Four wire RTDs we can obtain slightly better
compensation, but are generally found only in laboratory
equiptment and other areas where high accuracy is required.

Answer / kashyap ramavat

ys 3 lead wire is most widely used in industry...
but 4 lead wire is generally usd in LAB FOR CALIBRATION PURPOSE....as it GIVES MORE ACCURACY....

Answer / vikas dubey

3-wire construction is most commonly used in industrial applications where the third wire provides a method for removing the average lead wire resistance from the
sensor measurement. When long distances exist between the sensor and measurement/control instrument, significant savings can be made in using a three wire
cable instead of a four-wire cable.The 3 wire circuit works by measuring the resistance between #1 & #2 (R 1+2) and subtracting the resistance between #2 & #3 (R 2+3) which leaves just the resistance of the RTD bulb (R b). This method assumes that wires 1,2 & 3 are all the same
resistance..

4-wire construction is used primarily in the laboratory where close accuracy is required. In a 4 wire RTD the actual resistance of the lead wires can be determined
and removed from the sensor measurement.
The 4-wire circuit is a true 4-wire bridge, which works by using wires 1 & 4 to power the circuit and wires 2 & 3 to read. This true bridge method will compensate for any
differences in lead wire resistances.

Answer / b. ram thakur

to avoid led resistance when measure the temperature using 3 wire or 4 wire in RTD sensor

Answer / basker

above 200 m distance 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

Answer / lalit

FOR FULL COMPENSATION ONLY.

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