The difference is measurement accuracy. Using 2-wire resistance temperature detector (RTD) sensing provides good accuracy (maybe), the accuracy of 3-wire sensing is better, and 4-wire sensing provides the best accuracy. In addition, there’s the option of using Wheatstone bridge topologies to improve the performance of 2- and 3-wire RDTs. This FAQ begins with a review of the basics of RDT devices, looks at the tradeoffs between 2-, 3-, and 4-wire sensing, and closes with a brief look atWheatstone bridges和温度传感。
Designers can choose from thermistors and thermocouples in addition to RTDs. In many applications, RTDs are especially good choices due to their fast response times, repeatability, and superior sensitivities up to a few hundred µV/°C. And RTDs can be used over a wide range of –200°C to +800°C with a nearly linear behavior.
RTDs are available using various materials such as nickel, copper, and platinum. While platinum RTDs (PRTDs) can be more costly, other metals are not as widely used since they are not as stable or repeatable as PRTDs(Figure 1)。另外，PRTD不受腐蚀或氧化的影响。如果在工业，医疗和航空航天应用中，准确性和可重复性在-200至+800°C的温度中很重要，那么PRTD是最佳选择。
The development of modern PRTD standards such as IEC 60751 and ASTM 1137 allows substantial interchangeability of sensors between systems based on the specified tolerances and temperature coefficients. These standards make it easy to replace a sensor with one from the same or a different manufacturer while ensuring rated performance with minimal redesign or recalibration of the system. However, designers need to be aware that IEC 60751 was revised by the IEC in 2008 and again in 2022. IEC 60751:2022 introduced several significant technical changes. A review of those changes is beyond the scope of this FAQ.
The three most-common PRTDs are the PT100, PT500, and PT1000, which have resistances of 100Ω, 500Ω, and 1000Ω, respectively, at 0 °C. PT1000 is currently the most commonly-used PRTD type. RTDs are available for use in 2-, 3- and 4-wire configurations（图2）。
最简单的实现中的2线RTD配置，以及为RTD提供激发电流（i）的两条电线以测量传感器电压（以及温度）。由于计算出的电路的电阻包括导线和连接器中的电阻以及RTD元件中的电阻，因此结果将始终包含一定程度的误差。由于传感器电阻较低，甚至相对较低的电阻性（r）L）可能导致明显的测量不准确。
Using the shortest possible lead lengths and connectors with low contact resistances can reduce this error, but it’s impossible to eliminate it. A larger gauge wire with less resistance also helps minimize the error. In cost-sensitive applications that don’t require high accuracy, a 2-wire RTD configuration can be a viable option.
3条电线更好
The most common RTD configuration in industrial systems uses three wires to provide a good balance between cost and accuracy. Two wires connect the sensing element to the monitoring device on one side of the RTD, and one links to the other side of the RTD. If three identical type wires are used, and their lengths are equal, then RL1= rL2= rL3。指Figure 1above, a total system resistance is measured by measuring the resistance through leads 2, 3, and the resistance element (RL2+ RL3+ RTD）。仅导线的电阻可以通过铅2和3（r）测量L1+ RL2）。由于所有铅线电阻都相等，因此减去该值（rL1+ RL2）来自总系统电阻（rL2+ RL3+ RTD) leaves RTD, and an accurate temperature measurement can be made.
There are a couple of concerns with this approach:
- 仅当所有三个连接电线都具有相同的电阻时，测量才能准确。
- 在实用设计中，测量各种铅电阻可能具有挑战性。
If these concerns are not addressed, the basic 3-wire configuration is not necessarily an accurate way to measure temperature using an RTD. The 4-wire approach overcomes these challenges.
4条电线是巢
In a 4-wire RTD configuration, two wires link the RTD to the monitoring device (RL2and RL3， 在Figure 1）和另外两根电线（rL1and RL4) deliver the current used for measurement. Separating the excitation current wires from the measurement wires eliminates the sources of error found in 2-wire and 3-wire configurations. This configuration produces the most accurate measurements, but it’s the most complex, time-consuming, and expensive to implement.
桥梁以改进2线和3线测量值
Wheatstone bridge configurations can be used to obtain improved accuracy when using 2- and 3-wire RTD devices. To detect the small variations of resistance in an RTD in a 2-wire configuration, a temperature transmitter in the form of a Wheatstone bridge can be used (Figure 3A). The circuit compares the RTD value with three known and highly accurate resistors. In this circuit, when the current flow through the measuring device (V出去）为零，据说桥处于零平衡状态。这称为RTD温度输出的零或设定点。随着RTD温度的升高，V出去increases, and the temperature can be measured. If the RTD is installed some distance away from the Wheatstone bridge transmitter, the resistance of the wires changes as the ambient temperature fluctuates, introducing an error into the measurement. To eliminate this problem, a three-wire RTD Wheatstone bridge configuration can be used（图3b）。
在3线RTD Wheatstone桥配置中，连接电线（L1，L2和L3）的长度相同，因此具有相同的电阻。激发电流源连接到RTD的一端和Wheatstone桥。由于L1 = L2，因此电线的电阻取消，并消除了连接电线的效果。
Summary
When accurate and stable temperature measurements are needed, PT1000 RTDs are the most commonly used measuring device. The choice between 2-, 3- and 4-wire thermal sensing involves tradeoffs between increasing cost and complexity versus improved measurement accuracies. In some applications, Wheatstone bridge configurations can improve the accuracy of 2- and 3-wire sensing, but with increased complexities.
References
RTD测量的基本指南德克萨斯州Instruments
高准确的温度测量要求铂抗性温度探测器（PRTD）和精度三角洲ADC，Maxim集成产品
如何在RTD PT100与PT1000之间进行选择？, Omega Engineering
电阻温度计：电阻温度计和热敏电阻的原理和应用, Minco
RTD桥电路，流程技术和运营商学院
简单实现完全集成的4线RTD温度测量系统，用于高精度测量应用，模拟设备
提交以下：传感器提示
