Single CT (600/5A) to infeed PLC Analog card+Amp analog meter

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Hello,
i have Current Transformer 600/5A, it connected with Amps Analog meter (0-600A @class2.5).
i want to update without remove connection of old analog meter and update PLC analog input card +signal convertor 0-4mA,
my doubt is will take connection for both (measuring device) at same point of seconder CT? (like mess the connections both) please advice me?
(my signal convertor is Action Park 6800 with shunt Resistance 0.1ohm+PLC Analog input card).
here i attached my analog meter image
 

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  • #2
jim hardy
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i want to update without remove connection of old analog meter and update PLC analog input card +signal convertor 0-4mA,
I'd get a millivolt input Action Pak and use the existing meter as a shunt. Its probably 50 or 100 mv. If you're lucky the meter has studs on the back so you can wire right to them by just adding another nut.

upload_2016-5-7_5-50-40.png


edit i see Balun and i crossed in the mail.....
 
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  • #3
Baluncore
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The new shunt resistance of 0.1ohm will need to be wired in series with the old analogue meter and CT secondary.
Then the same current will flow through both meter systems. Check the calibration after you have modified it.

It is very important that you do not operate a CT with an open circuit output.
Make sure that the new meter can be disconnected without needing to remove the shunt.
 
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  • #4
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The new shunt resistance of 0.1ohm will need to be wired in series with the old analogue meter and CT secondary.
Then the same current will flow through both meter systems. Check the calibration after you have modified it.

It is very important that you do not operate a CT with an open circuit output.
Make sure that the new meter can be disconnected without needing to remove the shunt.
for my confidence to do i need connection diagram,of series resistance connection with Analog meter of CT Secondary .
if possible please provide to me.
Thanks for your support above
 
  • #5
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I'd get a millivolt input Action Pak and use the existing meter as a shunt. Its probably 50 or 100 mv. If you're lucky the meter has studs on the back so you can wire right to them by just adding another nut.

View attachment 100403

edit i see Balun and i crossed in the mail.....
for my confidence to do i need connection circuit diagram,of series resistance connection with Analog meter of CT Secondary .
if possible please provide to me.
Thanks for your support above
 
  • #6
jim hardy
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for my confidence to do i need connection circuit diagram,of series resistance connection with Analog meter of CT Secondary .
You've been offered two different approaches
1. Connect a high impedance Action-Pak millivolt transducer in parallel with the existing meter , and let it report the AC voltage developed across that meter to your PLC analog input.
2. Connect a 0.1 ohm Action-Pak AC current transducer in the CT circuit, in series with your meter, and let it report the resulting 0 to ½ volt AC signal to your PLC analog input

Post the wiring diagram of what you have now and the details of your existing meter and we could look at it.
But i won't guess at what you have and try to give detailed instructions based on a guess.
 
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  • #7
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Thanks again to your solutions.
here i attaching my circuit connection CT name( TP3)& explained in arrow marks.
my Analog meter back side is have screw studs, like your attached image in earlier post.
i expecting connection circuit help me.
my Action Park part number 6380-0000-1 ( Action model C006 resistor (0.1Ω, 5W, 1%) and set the input for 0-500mV AC)
 

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  • #8
jim hardy
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The ActionPak instructions seem pretty self explanatory.
http://www.actionio.com.cn/support/datasheets/actionpak/ap6380.pdf

It is a voltage measuring instrument with high input impedance, >100kΩ they say.
So it can sense voltage across a 0.1 ohm shunt that you add to the CT circuit if you wish, as shown in the instructions.
Or it can sense the voltage across something that's already in the CT like your existing meter. You will have to find what is the voltage across that meter at full scale indication so you know at what voltages to make the ActionPak's span and zero adjustments(see calibration on page 2 of instructions) .. I would expect to find between 50 and 100 millivolts. There are several meters on Ebay that say they're 60 millivolts full scale.

Snips from ActionPak instructions and your diagram.

PuttaCT1.jpg


Of course you can add the -.1 resistor in series with the meter and connect the ActionPak terminals 5&6 across it instead
and you'll run AC power to Action Pak 1&3, gnd to 2
and you'll run signal wire from ActionPak 7&8 to PLC analog in; i'd shield that one.
 
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  • #9
Baluncore
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I try to learn by others mistakes. Once upon a time, signals were taken from amplifier outputs that had moving coil meters. There were funny ripples in the data that turned out to be correlated with meter movements. The meters were acting as a motor / generator for some frequency components and so responded as a tuned element to steps in the signal. I doubt that will happen in this case with what appears from it's low end scale to be a moving iron meter.

But as the devil's advocate I must suggest that a moving iron meter will have a coil wound with copper wire. The Resistance of an element like copper is directly proportional to temperature, so for a +/–15°C variation you can expect a +/–5% variation in meter resistance.
On the other hand, the resistive shunt supplied with an ammeter will be made from an alloy with a very low temperature coefficient. That will probably now be an alloy of nickel, chrome and possibly some iron. Call it Nichrome.

When a moving iron meter is used as a current meter with a current transformer, the resistance variation of the meter is not important. But if you use the moving iron meter coil as a resistive shunt, any thermal variation in resistance will appear as a scale error on the new instrument. So, rather than use the moving iron meter as a shunt, I would advise wiring the new current shunt in series with the existing moving iron meter and CT secondary.
 
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  • #10
jim hardy
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Indeed it would be good to know the details about that meter.
The instrument technicians or electricians in your maintenance department should be able to help.

I didnt think about an iron vane movement. Wouldn't it he embarrassing if its impedance were a function of needle position?

@putta - you'd better check that before issuing the design package..
 
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