Richards Thermocouple Catalog 15

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Resistance Temperatu re Detectors
Wiring Configurations and Lead
(RTD's) - Platinum
Wire Color Codes
T3rpical RTD Wiring Configurations and Richards Color Codes -
The Two Wire RTD (Red, Black):
The Richards two wire RTD is constructed with only one red and one black lead wire. This type of sensor is the least accu-
rate form of RTD since it does not compensate for lead wire resistance. The total resistance of the lead wire will be added to the cal-
ibrated elements resistance. This will result in a higher temperature reading than is actually being measured. The error created by the
lead wire can be quit substantial if it is not compensated. The two wire RTD is the least common type of lead configuration.
The Three Wire RTD (Red, Black, Black):
The Richards three wire RTD is constructed with two black lead wires and one red lead wire. This is the most common con-
figuration for RTD sensors used today. The three wire RTD is more accurate than the two wire version since the instrument or trans-
mitter can use this third lead to compensate for added resistance and ambient temperature changes along the lead length.
The Four Wire RTD (Red, Red, Black, Black):
The Richards four wire RTD is constructed with two black lead wires and two red lead wires. lt is the most accurate RTD
configuration since the instrument or transmitter can completely compensate for lead wire resistance and ambient temperature
changes along the leads. The four wire RTD can also compensate for errors caused by mismatched lead wires (does not occur often).
This is accomplished by passing a current through the outer leads (First Red + First Black) and measuring the voltage drop across the
inner leads (Second Red + Second Black). The instrument or transmitter can than calculate the resistance of the element alone. These
sensors are not as common as the three wire version. They are only used where very high accuracy is critical. Four wire RTDs can
be used as a three wire or two wire by removing one of the red leads or one of the red and one of the black leads.
Note: The lead color codes below are Richards standards. There is not an industry standard tor lead color codes.
Red Red
Red
Wire-
Black
Black
Wire-
Black
Black
Black
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