Power Measurement

How would you connect a current transformer to a PLC analog input module?

rshultis said:

How would you connect a current transformer to a PLC analog input module?

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You would almost certainly need some sort of signal conditioner, preferably a well-isolated one.

It would be helpful to know more about the specific application, but, absent that data, here's some things to get you started looking at the right kind of stuff to get it done.

Red Lion makes products that integrate a signal conditioner with a CT. Here are some links:

CTR True RMS AC Current Transducer

CTL Current Average Responding Transducer

CTD DC Current Transducer

{DISCLAIMER: No, I don't work for Red Lion, but I have found their stuff to be very useful in times past. With any controls application, the designer/implementer should always do their due diligence and assess for themselves the usefulness or fitness for a particular application of any piece of equipment.}

If I read you correctly, you already have a CT? You'd have to determine what its output is, and select a proper signal conditioner for it. Usually, CTs output in the millivolts, and you would need to convert that to a range acceptable to the PLC's analog inputs (usually either a current loop or voltage input, depending on the PLC, the input module, etc.)

There are many other vendors which make signal conditioning gadgets besides Red Lion. You might look at something from Moore Industries, Action Pak, or any of several others before you find what suits your application and price/performance point best.

Some examples of stand-alone signal conditioners that might suit your needs:

Action Pak Model AP6380

Moore Industries Signal Converter Selection Guide

Of course, if you are working outside the U.S., you may wish to consider other vendors that are more local, and I don't really have a clue there.

The tricky part is selecting a signal conditioner with enough input range to be able to calibrate it properly, and then having the prime standards (precise enough test equipment in this case) against which to calibrate it. It makes a good case for the more integrated CT/signal conditioner all in one transducer if the accuracy of the application is critical, since they are usually already well matched.

Here's wishing you all the best with your project.

Later On,
D

rshultis said:

How would you connect a current transformer to a PLC analog input module?

Click to expand...

To be a bit smart ***:
I would use wires.
OK got that out of my system

You are no longer restricted to current transformers whose output is 5 A.
1. Determine input on PLC ie 0 to 20 mA 4 to 20 mA 0 to 10 volt etc etc and whether AC or DC.
2. Once you know PLC end then pick a current transformer whose output matches the PLC input.

Dan Bentler

leitmotif said:

To be a bit smart ***:
I would use wires.
OK got that out of my system

Click to expand...

Yeah, I forgot that bit... probably want to use a shielded, twisted pair? (You're a funny guy, Dan... I like that.)

You are no longer restricted to current transformers whose output is 5 A.
1. Determine input on PLC ie 0 to 20 mA 4 to 20 mA 0 to 10 volt etc etc and whether AC or DC.
2. Once you know PLC end then pick a current transformer whose output matches the PLC input.

Dan Bentler

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Dan's right. It's a big, fast-moving world out there, and technology is constantly changing - part of the challenge of this job we do is mating old technologies with new stuff that's coming out to do the job with the best mix of both that is cost-effective, reliable, and accurate.

Best of Luck,
D

Thank you all very much.

4-20 mA output

I just finished installing 12 CT's on the mains in our plant. The problem I had was finding CT's that were compatible with the data logger I have, which required a DC input signal, therefore requiring conditioning as mentioned before. Adding that to the price of each CT was expensive. Finally I found the best product of all those I had researched, from a company in KOREA(they don't have direct distribution here yet). The model we are employing takes 0-500A input, giving a 4-20mA output. Best part is the company couldn't be more of a pleasure to work with and I got Split-Core CT's in a big diameter for less than all the others I researched.....All the stuff I was finding was usually solid core(no chance to shut down to slide over huge power wires) and often too small for the wires I wanted to measure. I ordered 2 to try em out, and they worked great so I ordered 11 more. They gave me a discount for the volume purchase and I ended up getting them for about 1/2 what a 4-20mA from automation direct was asking(and AD's were solid core to boot)

The company is called J&D Electronics Co. Ltd.
http://www.hqsensing.com /

KNeland said:

I just finished installing 12 CT's on the mains in our plant. The problem I had was finding CT's that were compatible with the data logger I have, which required a DC input signal, therefore requiring conditioning as mentioned before. Adding that to the price of each CT was expensive. Finally I found the best product of all those I had researched, from a company in KOREA(they don't have direct distribution here yet). The model we are employing takes 0-500A input, giving a 4-20mA output. Best part is the company couldn't be more of a pleasure to work with and I got Split-Core CT's in a big diameter for less than all the others I researched.....All the stuff I was finding was usually solid core(no chance to shut down to slide over huge power wires) and often too small for the wires I wanted to measure. I ordered 2 to try em out, and they worked great so I ordered 11 more. They gave me a discount for the volume purchase and I ended up getting them for about 1/2 what a 4-20mA from automation direct was asking(and AD's were solid core to boot)

The company is called J&D Electronics Co. Ltd.
http://www.hqsensing.com /

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would you happen to have the part number?

diat150 said:

would you happen to have the part number?

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Here's another option, see link

http://www.loadcontrols.com/products/products.html

im looking for cheap. I just want to monitor my current usage of my home. on top of that, I want to monitor how long my ac runs, temp in the house, temp in the attic, and possibly temp in one of the ducts.

I see some of those cheap korean ct's that plug into multimeters on ebay for like 20 bucks. might even use one of those if it works properly. I would use a phoenix contact signal conditioner to convert from mv to ma.

500A, 4-20mA output

The model CT I got from J&D:

JC36S500-RMS

I paid $96 each when I bought 2, and $84 each when I bought 11 of them. They are loop powered, so I grabbed a 24V power supply I had sitting around for power. The convenience of split core design was necessary for our application, and when comparitive shopping the price was great(including the shipping FedEx from KOREA). These would definitely be overkill for a persons house(one panel I was in is a 3000A panel) but for industrial applications work great.

diat150 said:

im looking for cheap.

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You might find this page useful for a home project.

http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm

Most modern KW hour meters I see now days have an LED that blinks in time with Power used, just monitor that pulse rate, to calculate watts used.

The bit I would like to find is a commercially made sensor to watch that LED pulse rate and feed it as a 24 volt DC input to a PLC
It would look alot better than my home rolled piece of bits.

diat150 said:

im looking for cheap. I just want to monitor my current usage of my home. .

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you don,t. use a signal converter to convert 0 - 5 amps to 4 - 20 ma