库卡 KRC2/VKRC2 伺服系统 

所示电路可连接到2线、3线或4线RTD,大可测量3.92kΩ电阻，因此它适用于Pt100和Pt1000RTD。使用电流激励，电阻测量为RTD与3.92kΩ精密基准电阻(RREF)之间的比率式测量结果。所示，RTD测量在AIN1和AIN3之间进行，REFIN1+和REFIN1-用作测量的基准输入。线模式:仅AIN0上的激励有效，设置为250 μA,线模式:AIN0和AIN4上的激励电流均有效，各设置为100μA,线模式:仅AIN0上的激励有效，设置为250 μA。

The circuit shown can be connected to a 2-, 3- or 4-wire RTD and measures up to 3.92kΩ resistance, making it suitable for Pt100 and Pt1000 RTDs.Using current excitation, the resistance measurement is a ratiometric measurement between the RTD and a 3.92kΩ precision reference resistor (RREF). As shown, RTD measurements are made between AIN1 and AIN3, with REFIN1+ and REFIN1- used as reference inputs for the measurements. Line mode: Excitation on AIN0 only is valid and set to 250 μA,Line mode: Excitation current on both AIN0 and AIN4 is valid and set to 100 μA each,Line mode: Excitation on AIN0 only is valid and set to 250 μA.

使用高端电流检测技术。 对于较低的RTD引线电阻值，此技术可降低3线模式下电流失配的影响,基准电阻(RREF)选择为3.92 kΩ，高支持850°C的Pt1000 RTD测量（850°C时RTD电阻为3.9048 kΩ）。 RREF的值必须根据RTD的大预期电阻来选择。 RREF电阻的精度直接影响测量精度，因此，必须使用精密、低漂移电阻。 

High-end current detection technology is used. For lower RTD lead resistance values, this technique reduces the effect of current mismatch in 3-wire mode. The reference resistance (RREF) is selected to be 3.92 kΩ, which is high enough to support Pt1000 RTD measurements at 850°C (RTD resistance of 3.9048 kΩ at 850°C). The value of RREF must be selected based on the large expected resistance of the RTD. The accuracy of the RREF resistor has a direct impact on the measurement accuracy; therefore, precision, low-drift resistors must be used.

4线模式下，激励电流必须设置为250 µA，3线模式下设置为100 µA。 对于4线模式，假设RTD值为3.92 kΩ。 来自AIN0的激励电流流经RREF + RRTD + RRETURN = 3.92 kΩ + 3.92 kΩ + 3 kΩ = 10.84 kΩ。 因此，AIN0处的电压等于250 µA × 10.84 kΩ = 2.71 V。AD7124-4指定激励电流输出端的输出顺从电压为AVDD − 0.35 V，即3.3 V – 0.35 V = 2.95 V。 因为2.95 V > 2.71 V，所以即使对于大RTD电阻，250 µA激励电流也能正常工作。

The excitation current must be set to 250 µA for 4-wire mode and 100 µA for 3-wire mode. For 4-wire mode, assume an RTD value of 3.92 kΩ. The excitation current from AIN0 flows through RREF + RRTD + RRETURN = 3.92 kΩ + 3.92 kΩ = 10.84 kΩ. Ω + 3 kΩ = 10.84 kΩ. Therefore, the voltage at AIN0 is equal to 250 µA × 10.84 kΩ = 2.71 V. The AD7124-4 specifies the output compliance voltage at the excitation current output as AVDD - 0.35 V, i.e., 3.3 V - 0.35 V = 2.95 V. Since 2.95 V > 2.71 V, the 250 µA excitation current works even for large RTD resistors.