库卡 00-168-334 伺服系统

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.
 

 在3线模式下，来自AIN4的引脚补偿激励电流也会流经3 kΩ返回电阻，在AIN0处产生一个附加电压：250 μA × 3 kΩ = 0.75 V。因此，AIN0处的总电压等于2.71 V + 0.75 V = 3.46 V，这违反了裕量要求。 所以，在3线模式下，各激励电流必须降至100 μA以提供足够的裕量。 

In 3-wire mode, the pin-compensated excitation current from AIN4 also flows through the 3 kΩ return resistor, generating an additional voltage at AIN0: 250 μA × 3 kΩ = 0.75 V. Therefore, the total voltage at AIN0 equals 2.71 V + 0.75 V = 3.46 V, which violates the margin requirement. Therefore, in 3-wire mode, the individual excitation currents must be reduced to 100 μA to provide sufficient margin.