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这个现象是由于9216/26接线端至接线盒电阻和接线盒内部电阻不一致引起。在做四线制测量时不存在这个现象。三线制测量时RTD+和COM两路的电阻不一致会导致额外的误差。
可以通过校准或者调整来补偿这个误差。将RTD+和RTD-短接,将RTD-和Com短接。将电阻值读出后,在以后的读值中减去这个值进行补偿。
在减去这个值时要注意在将电阻值转换为温度之前操作。将电阻转换为温度有一个函数,Convert RTD Reading.vi,这个函数在函数选板>>数值>>转化中。 还有一个函数可以将电阻转化为温度,RTD to Temp.vi,可以在下面找到。
这个校准/微调可以被跳过,而除此之外的在NI9216/9226数据手册中指出的由三线制测量引起的误差也可以由这个方法进行补偿。
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