AI835 ch8 as cold junction

I am working on one project, the susyem is AC800M PM856 + AI835 for industrial frunace project.

If I use all 8 channels of AI835 as TC input, the error is about 5 degree, same for 3 boards, we used a gauge meter to simulate TC signals.

So I used Ch 8 as cold injunction, connected to one 4-wire PT100 RTD, connected as shown in the manual. but It doesn't work. Ch8 shown a triangle error, I dn't know what is wrong?

in the property tab, I set channel 1 to7 measured via channel 8, set ch 8 Pt100, -40~100. also has one variable connected to ch8.

thanks

zhanhg/zhihong, former ABB service engineer.

zzh1967ca@hotmail.com

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zhang/zhihong Rank: 3051

Asked 3 years ago

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Hi,

the cjt setting is measured via ch8 for ch8 also ? it should not be fixed junction temp.

Then you have not mentioned which TU you are using but check connection should be as mention below w.r.t TU830

Also take a note where RTD should be placed ?

I recommend to test first using FJT(fixed junction temperature) if the TC reference junction temp. is not varying and remains stable or almost fixed. For this you need to select second option in marked circle above. as well as enter FJT value in 'C in module parameter.

Also check if you are getting row values for all the channels and using some scale block or you are getting direct physical value ? if there is any scaling blocks check input/output range to convert row value to physical value ! you get row values in memory map doc.

Hope that helps.

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by zhang/zhihong Rank: 3051 on 8/25/2014 1:24:18 AM | Like (0) | Report

Thank you very much for your support. I called the customer to check the wire, by mistake , they jump L1+ and L2+ as the AI810+TU810 did,The ch8 now shown the right value, 27.8 degree. Ch1~ch7 will be ckecked tomorrow. I am travelling to the site.

by zhang/zhihong Rank: 3051 on 8/25/2014 7:27:46 PM | Like (0) | Report

I am in the customer's site. The peoblem is, The AI835 are installed in the cabinet, when the machine runs, the environment temp inside the cabinet change, the value of Ch8 measuring via the PT100 also change, C1~7 also change values accordingly, this method for measuring the furnace cannot be accurate. The customer need to calibrate every channel, so we need to setup an fixed offset, Did anybody make it via changing the fixex parameter like 25 degree or other way?

by Sumit Gargav AKS expert

Rank: 3 on 8/25/2014 7:40:59 PM | Like (0) | Report

Ok, then as mentioned above fixed offset you can set via selecting option "fixed junction temperature" instead of CJT via ch8. for all channels, note that if you use this option you get ch8 spare and that you can use for measuring field temperature. Set fixed value of offset(room temp) in module parameter in 'C. Hope that helps.

by brluson Rank: 522 on 8/27/2014 6:20:42 AM | Like (0) | Report

Hi, maybe you could move the Cold Junction outside your I/O cabinet, like a junction box. If your junction box does not have any heat sources the temperatura inside will be almost the same in the whole cabinet. Then you move your Pt100 to the junction box and connect the junction box to the I/O using cooper cable (Cu). The compensation will be very accurate. I have already used this several times.

BR\

Luciano Sonoda.

by zhang/zhihong Rank: 3051 on 8/28/2014 8:49:40 AM | Like (0) | Report

Hi Luciano, you are right,Thank you for your support. We installed the AI835+TU810 in the electrical cabinet. The cabinet has air cooling unit. I found that the compensation is very accurate in the morning when we switch the power, After a few minutes, the compensation is not accurate, we found he reason is the cooling air make the environment temp unstable. Then I covered this AI835 Unit and reduce the direct blow from the air, It became more accurate. I am trying to put this AI835 Unit in a junction box inside the cabinet, then we should get a very accurate result.

by brluson Rank: 522 on 8/28/2014 9:07:27 AM | Like (0) | Report

This option looks fine, but watch the temperature of the module, maximum temperature in operation is 55ºCelsius with Din rail in horizontal position. If you move just the could junction (by that I mean cold junction and Pt100 reference) you can solve your problem.

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Sumit Gargav AKS expert

Rank: 3

Answered 3 years ago

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AI835 ch8 as cold junction

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