CTs to 1756-IF4FXOF2F

[TimWilborne 108]

I need to do some current measurement and was wondering if anyone has an idea how to hook CTs to this Controllogix module? Or in general to a Controllogix? I already have the module on the machine. Beyond that is is all motion, discrete I/O, and an Ethernet module

[snk 0]

Isn't it just an analog input?

[Ken Moore 23]

Have you puchased the CT's yet? I use this brand a lot: http://www.nktechnologies.com/products_cur...transducers.htm Output is standard 4-20mA, some models also have 0-5VDC or 0-10VDC, works with any standard analog input card.

[TimWilborne 108]

No I haven't purchased the CTs yet. The 1756-IF4FXOF2F can do current or voltage. The NK Technologies CTs look good but leave it to me to leave out a small detail . This is just something I am debating on whether to put on a machine or not but the max amperage would be 1390 amps, 50,000 amps, either or both. Looks like the ATR4 or the ATPR4 would handle the low amperage, do you think I'm out of luck on the high amperage? What is the advantage of the Powered Transducer?

[Ken Moore 23]

I assume you mean loop powered. Most of my instruments are located in Class I, Div I or Div II areas and are connected via I.S. (intrinsically safe) barriers. These instruments are all loop powered, so all my wiring is setup that way. When ever I get a device that provides it's own loop power, it's a pain, I either have to change the enclosure wiring or buy an isolator. I'd give them a call about the high amp unit, when I first contacted them about a potential project, they were extremely helpful, and provided a sample unit for me to "play" with.

[TConnolly 13]

TW, for high current CTs which you will interface to a PLC I strongly suggest you look at these guys. https://www.ohiosemitronics.com/ We use their products on the kinds of systems you and I have been discussing. They are particularly well suited to the non-sinusoidal outputs of SCRs.

[TimWilborne 108]

Well it's no secret, I'm rebuilding a flash welder. The main reason I didn't mention it is since I don't have enough knowledge yet to answer questions. Example - non-sinusoidal outputs of SCRs. So it does? Alaric and another fine gentlemen on this forum have been helping me with the SCRs. Peter has helped me here and on several other forums with the hydraulics. Might as well make it public, would you suggest putting the CTs on the primary or the secondary side of the transformer?

[TimWilborne 108]

How about as far as hookup? Do you put them on the primary side along with the SCR or on the secondary side?

[Craig 0]

If you use the primary side the current ratio will be a lot less you can step them down even further by just using two CT's until you get to the right ratio. Your frequency of switching is going to be pretty high so normal ct's with iron cores will be no good you will need some with ferrite cores. At the high current you are talking about I would step down with the ct's then use an loop isolating transducer probably an optical one. as you don't want a mess. The current reading is probably not going to be that accurate as the SCR switching will produce alot of harmonics. AN easier way is just to take a look at what the firing rates for the SCR's are and calculate the RMS current from that and them make the big ASSUME from there.

[TimWilborne 108]

Yes, I do this now and will probably just continue doing it but was toying with the idea of actually putting CTs on it. I'm not thinking that it will be worth it Thanks for your suggestions TW