RTD is a temperature responsive device consisting of one or more sensing platinum resistors within a protective sheath, internal connecting wires and external terminals to permit connection of electrical measurement instruments. Mounting means and connection heads may be included.
| 2 Wire: In 2 wire RTDs, one lead wire is connected to each wire of the RTD element. 2 Wire RTDs are an economical option for the applications where high accuracy is not required. Since there is no compensation wire, the accuracy of RTD can be affected if long lead wire is used. 3 Wire : 3 wire RTDs are the most common type of RTDs used in the industry. In 3 three-wire Rtd 1 wire is connected to the one side of the RTD element, and on the other side, 2 wires are connected to compensate for the resistance. With compensating wire, accuracy is very close to the element accuracy at the termination end. 4 wire: 4 wire RTDs are highly accurate. In 4 wire RTDs 2 wires are connected to each side of the RTD element. With additional wire on each side of the RTD element, the output at the termination is highly accurate. 4 wire RTDs are recommended where high accuracy and long lead wire is required. |
| Element Type | Pt100 | Pt200 | Pt1000 | Ni120 |
| Wire Wound Ceramic | x | x | ||
| Thin Film | x | x | x | |
| Alpha Value | IEC 0.003850ºC JIS 0.003916ºC | IEC 0.003850ºC | IEC 0.003850ºC | 0.00672ºC |
The tolerance values of resistance thermometers are classified in Table 3. These tolerances apply for thermometers of any value of R0. Where the specified temperature range of a particular thermometer is smaller than in this table, this shall be stated.
