34980A 4线电阻测量得到负值

你尝试过使用偏移补偿吗？
（SENS：FRES：OCOM ON，（@）。我怀疑有一些热电偶效应会产生干扰测量的电压。



     以下为原文

  Have you tried using offset compensation? (SENS:FRES:OCOM ON,(@).   I suspect that there is some thermocouple effect that is generating a voltage that is interfering with the measurement.

是的，经过一段时间阅读手册并查看所有可编程参数后，我们激活了偏移补偿。
激活此参数后，我们对温度变化的响应速度更快，系统不会产生太大的负值。
即使我们仍然有一些负面价值。
我们进行的一项测试是直接在4W通道的所有四个连接之间的接线端子中做短路。
读取该通道上的值，我们在两种情况下都得到负值（偏移补偿与否）。
如果我们增加接线端子的温度，我们会得到负电压的负增加，如果我们冷却它，我们会得到正电阻的增加是否有任何文件解释了安捷伦使用的4W测量方法。
我们无法准确理解如何，但似乎不同时采取电压和电流测量。
因此，如果阻力随时间变化（由于温度变化）会导致奇怪的结果。



     以下为原文

  Yes, after some time reading the manual and seeing all the programmable parameters we activated the Offset compensation. 

With this parameter activated we have a faster response to the temperature changes and the system does no get too negative values. Even that we still have some negative values. 

One of the test we made was making a short directly in the Terminal block between all four connections of a 4W channel. Reading the value on that channel we get a negative values in both cases (Offset compensated or not). If we increase the temperature of the terminal block we get negative increases of the resitance and if we cold it down we get positive increases of the resistance

Is there any document that explains the method of 4W measures used by Agilent. WE can not understand exactly how, but it seems that Voltage and Amperage measures are not taken at the same time. So if resistance is changing along in time (due to temperature changes) can lead to strange results.

我相信这个34980A数字万用表需要进行校准以消除负电阻偏移。
34980A不测量电阻测量的电流源。
它是一种已知值的精密校准电流源，其稳定性高。
虽然我没有改变接线盒的温度，但我没有看到任何带有短路的负读数。
我确实看到，如果改变电流源极性，它将读取负电阻。
我认为这是故意这样做的，你可以看到电流源的极性。
1欧姆或更低值的精度为范围的+/- 0.004％，因此对于最低100欧姆范围，对于Tcal +/- 5℃范围内的温度，其为+/- 0.004欧姆。温度系数为
超出该范围0.0005欧姆/℃。
我会再看一下这个。



     以下为原文

  I believe this 34980A DMM needs to be calibrated to remove a negative resistance offset.   

The 34980A does not measure the current source for resistance measurements.  It is a precision calibrated current source of known value that is stable over the .   

I was not able to see any negative readings with a short although I didn't vary the terminal block temerature.  I do see that if you change the current source polarity, it will read negative resistance.  I think this is intentionally done so that you can see the polarity of the current source.

The accuracy for values of 1 ohm or less is +/- 0.004% of the range, so for the lowest 100 ohm range, it's +/- 0.004 ohms for temperatures in the range of Tcal +/- 5 C.  The temperarure coefficient is 0.0005 ohms/C outside that range.

I'll look into this some more.