There are limitations for RTDs (resistance temperature detectors), so knowing the difference between each type is an essential part of proper engineering and functionality. The most common RTDs include 2-wire, 3-wire, 4-wire sensors. To pick the proper sensor for your application, you need to know the basic differences.
Two-Wire RTDs are the most simplistic versions because they are only a wire resistor. These resistors only have two leads, which means that resistance increases as temperature goes up. The highest quality RTDs are constructed with platinum wires because they offer linear and predictable resistance. When platinum is applied to two copper wire leads, the resistance of the wire goes up drastically. The longer the wire lead, the more resistance the wire has.
Three-Wire RTDs are a great option for avoiding lead wire resistance. The three-wire variant is often seen as the most commonly used configuration because they are robust and accurate. The three wires contain a single lead attached to a terminal, and the other two wires are connected to the terminal of the RTD. For the sake of consistent performance, all wires are constructed from the same material, are the same length, and have an approximately equal resistance throughout.
Four-Wire RTDs have a similar principle as a three-wire variant. The main difference between these two RTDS is that a four-wire version has two wires attached to both terminals. Although they are typically more expensive than the two versions listed above, they are the most accurate RTD.
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