如何使用34980A构建多ch TC模拟器？

你实际上需要一个像Fluke 5520A这样的热电偶模拟器，我不记得究竟是如何工作的。
不知何故，它必须补偿34921T中参考结的温度。
我记得它实际上非常简单，但它现在还没有找到我。
34921T输入端子处的热电偶电压是测试热电偶相对于0C的电压与参考结温度下热电偶相对于0C的电压之间的差值。
参考结温越高，34921T端子的电压越低。
因此，如果您只是将端子上热电偶类型的温度与电压表中的热电偶电压放在一起，34980A将读取测试热电偶温度+参考结温度。
这有点难以想象。
我建议您在Keysight网站上查找Keysight 34980A并找到应用说明290“实际温度测量”并查看热电偶部分。
完成此任务的最佳方法是什么？
我们应该关闭内部数字万用表并使用其中一个模拟总线来获取每个通道的DCV信号吗？
各个点的冷补偿怎么样？
- 您可以这样做，但由于上述原因，您将无法获得正确的温度读数。
这完全是关于冷端补偿。
我们是否应该让内部DMM运行并设置为将每个通道测量为K型，然后将DCV电源连接到公共总线（馈入内部DMM）并施加不同的电压？
我认为被测单元和349890A都表示相同的温度。
- 你有上面讨论过的同样的问题。



     以下为原文

  1. You actually need to have a Thermocouple simulator like the Fluke 5520A for that and I can't remember exactly how that works.  Somehow it has to compensate for the temperature of the reference junction in the 34921T.   It's actually pretty simple as I recall, but it's not coming to me right now. 

The thermocouple voltage at the 34921T input terminals is the difference between what would be the test thermocouple voltage relative to 0C and the voltage from a thermocouple at the reference junction temperature relative to 0C.   The higher the reference junction temperature, the lower the voltage seen at the 34921T terminal.  So if you just put the thermocouple voltage from the table of temperature versus voltage for the thermocouple type on the terminals, the 34980A would read the test thermocouple temperature + the reference junction temperature.  This is a little difficult to visualize.  I recommend you look up the Keysight 34980A on the Keysight web site and find Application note 290 "Practical Temperature Measurements" and look up the section on thermocouples.

What is the best way to accomplish this?
Should we turn off the internal DMM and use one of the analog busses to get the DCV signal to each channel?  What about cold compensation at the various points?
- You can do that, but you won't get the correct temperature reading for the reasons discussed above.  It is all about the cold junction compensation.

Should we leave the internal DMM operational and setup to measure each channel as a type K, then connect the DCV supply to the common bus (feeding the internal DMM) and apply different voltages?  I think the unit under test and the 349890A would both indicate the same temperature.
- You have the same problems discussed above.

谢谢您的帮助。
现在还不清楚会发生什么，但这是我（简单）的理解。
如果我们仅根据TC材料和CU来考虑该电路，则只需要两个需要冷端补偿的地方。
1）在UUT的输入端（我们正在校准的PLC输入模块）（T1）。
2）3491T等温接线端子（Cu），其中来自UUT的TC导线着陆，（T2），在这个例子中使用通道01。
我们现在有两个测量仪器相互连接输入，因此它们基本上都是测量开放式TC。
无论存在什么噪声，都会转换为某些模糊温度读数，这些温度读数已由每个单元冷端补偿（CJC）校正。
CJC - 我相信34980A将测量T2，根据34980A中编程的TC计算电动势，然后通过该电动势值数字地偏移34980A DMM读数。
如果我们将另外两根导线（Cu）连接到相同的3491T CH01输入端子（也是Cu），然后通过这些铜线施加额外的电压，DMM仍将读取CH01处的电压并仍然被数字偏移
T2 CJC值。
这些卡片应该在几天之内就可以了，我们将把它们全部连接起来，看看它是怎么回事。



     以下为原文

  Thanks for the help.  It's still not clear what will happen, but here is my (simple) understanding.

If we think of this circuit only in terms of TC material and CU, there are only two places where cold junction compensation are needed. 
1) At the input of the UUT (which is the PLC input module we are calibrating) (T1). 
2) The 3491T isothermal terminal block (Cu) where TC wires from the UUT are landed, (T2), lets use channel 01 for this example.

We now have two measuring instruments wired to each others inputs so they are both basically measuring an open TC.  Whatever noise is present will be converted to some ambiguous temperature reading that has been corrected by each units cold junction compensation (CJC).

CJC - I believe the 34980A will measure T2, calculate an emf based on what TC has been programmed in the 34980A, then digitally offset the 34980A DMM reading by this emf value.

If we connect 2 more wires (Cu) to the same 3491T CH01 input terminals (which are also Cu), then apply additional voltage through those copper wires, the DMM will still be reading the voltage at CH01 and still be digitally offset by the same T2 CJC value.

The cards should be here in a few days and we'll connect it all and see how it goes.

我将不得不研究这个并回复你。
它在这里非常忙碌而且我落后了。
您可能需要研究附带的实际温度测量应用说明的热电偶部分。
如果您可以附上您的设置图纸，对我来说也会非常有帮助。



     以下为原文

  I'm going to have to study this and get back to you.  It's gotten very busy around here and I'm way behind.  You might want to study the thermocouple section of the attached Practical Temperature Measurements application note.  Also it would be very helpful to me if you could attach a drawing of your setup.

附件

• Practical Temperature Measurements.pdf1,018.7 KB
  

“CJC - 我相信34980A将测量T2，根据TC h计算一个电动势



     以下为原文

  "CJC - I believe the 34980A will measure T2, calculate an emf based on what TC h