Need cheap way/product to produce acurrent at very low voltage.

  • Thread starter mikeryan
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  • #1
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Main Question or Discussion Point

I need to produce at 0-5AAC in the millivolt range to test a current to current transducer. The ac amp source to the XDCR is from a 150:5 CT which is then converted to a 4-20mA signal. If my company had the money I would go with an Arbitor panel meter calibrater but that's not an option.

Any suggestions?
 

Answers and Replies

  • #2
dlgoff
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Welcome to PF mikeryan.

Why do you need the source to be in the millivolt range? The transducer should only be concerned with current not voltage.
 
  • #3
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Welcome to PF mikeryan.

Why do you need the source to be in the millivolt range? The transducer should only be concerned with current not voltage.
I'm actually not sure if the voltage is that big of and issue. I was comparing the imput signal another CT to another XDCR and it was 3AAC(at the time) at 175 mV. I just don't want to burn something out.

What I want to do is calibrate the 4-20mA output(to DCS net.) which is indicating motor current. My engineers think ther is insufciant power management because the 4-20 is out of cal. but I don't have anything to produce a 0-5AAC to confirm this, short of loading up the 1000hp motor.
 
  • #4
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OK. You can produce a 4 milliamp signal with a 1250 ohm resistor (a 100 ohm plus a 250 ohm resistor) in series with the 5 volt AC supply. You can produce the 20 milliamp signal from the same 5 volt AC supply by putting it in series with a 250 ohm resisotor (four 1000 ohm resistors in parallel.
 
  • #5
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The 4-20 mA isn't what I need to produce. I need the 0-5AAC to supply the xdcr which in turn is converted to the 4-20 mA that I need to cal. The xdcr takes the 5AAC off the motor CT and sends the 4-20 out.
 
  • #6
887
98
So what you're looking for is variable low voltage AC power source capable of delivering up to 5 amps and a calibrated amp meter?
 
  • #7
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Yes, and I already have all the calibration equipment I need, except, of course, for the 0-5AAC source.
 
  • #8
887
98
Ok, I have an idea for you. It's cheap and you may already have everything you need. Don't laugh because it just may work. All you need is a 120 volt variac (variable transformer) and a gun type electric soldering iron. Remove the tip from the soldering iron and use it's output as your low voltage ac supply. Connect the ac power plug of the soldering iron to the output of the variac. And that's it. Use the variac to adjust the current output. I have a Weller soldering iron here and I measured the output voltage as 345mv with the cord pluged into the wall outlet. So with the variac you should be able to adjust it down to whatever you need.
 
  • #9
dlgoff
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Or maybe just the variac and an electric range element (in series with your meter of course).
 
  • #10
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digoff said:
Or maybe just the variac and an electric range element (in series with your meter of course).
That would be more dangerous. And the variac would have to be able to supply 5 amps. The variac could be any size (even the smallest) when used with the soldering iron.
 
  • #11
dlgoff
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The OP is working with 150:5 CTs. I think he knows the hazards involved and will take the proper steps to ensure that he doesn't get hurt.
 

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