AdvancedHMI Software

General Category => Open Discussion => Topic started by: MrPike on January 25, 2018, 04:58:20 PM

Title: 4-20 mA AC output
Post by: MrPike on January 25, 2018, 04:58:20 PM

I am hoping to leverage the controls experts on this forum to see if there is a device or output card that will give me milliamperes AC output from a PLC. I'm working on a project that I want to control AC mA to a device. This can be in the form of a converter or direct PLC output card. I can work with any range of mA but I figure 4-20 would be my best bet. For that matter a variable resistance output would work and I can supply the AC voltage. I am using GE PACS controllers. Thanks for any info.

Title: Re: 4-20 mA AC output
Post by: Phrog30 on January 25, 2018, 06:06:02 PM

4-20mA AC? Are you sure? Do you mean DC?

Title: Re: 4-20 mA AC output
Post by: MrPike on January 25, 2018, 07:17:27 PM

Nope. I'm looking for an AC output. I know it's not standard but looking if anyone has come across something before. I want to drive the secondary of a current transformer.

Title: Re: 4-20 mA AC output
Post by: jazzplayermark on January 25, 2018, 08:17:53 PM

Can you explain more about what you're trying to accomplish? By nature an AC signal is not a steady current.

Title: Re: 4-20 mA AC output
Post by: MrPike on January 25, 2018, 09:11:27 PM

Sure.  I'm trying to drive the 5 amp CT input to a power meter with a PLC program so I can create a simulated load on the meter.  To accomplish this, I am using a PLC wired to the secondary of the CT  and inputting the CT primary into the meter.  I just need to be able to alter the mA in the secondary.  I have done this manually in all fashions but want to automate it so I can emulate dynamic loads

Title: Re: 4-20 mA AC output
Post by: jazzplayermark on January 26, 2018, 11:46:26 AM

Do you by chance have three CT's?  If so, you might be able to use the 4-20 to drive a VFD and use the CT's in place of an actual 3 phase motor. Obviously you'd have to size accordingly. Just a thought.

Title: Re: 4-20 mA AC output
Post by: Archie on January 26, 2018, 12:07:18 PM

My thought is along the lines of a function generator with amplitude controlled by a 4-20mA signal. Every signal generator that I have ever used is controlled by a potentiometer. So if the was a way to convert 4-20mA to a potentiometer signal, it may get you there.

Title: Re: 4-20 mA AC output
Post by: billerl on February 09, 2018, 08:30:54 AM

http://www.advantech.com/products/7447e150-338d-402d-b5a1-c9ce6d98816e/adam-6224/mod_8e33d21a-7b6c-4175-9029-cfbdaa15b723 (http://www.advantech.com/products/7447e150-338d-402d-b5a1-c9ce6d98816e/adam-6224/mod_8e33d21a-7b6c-4175-9029-cfbdaa15b723)

Maybe check these out. I would assume these are for DC, but I don't see where it specifies AC or DC output. I have successfully used Advantech modules with Modbus TCP and AHMI in the past.

Title: Re: 4-20 mA AC output
Post by: jazzplayermark on February 09, 2018, 11:53:23 AM

These are nice modules but they are strictly DC.

Title: Re: 4-20 mA AC output
Post by: seth350 on February 16, 2018, 08:23:23 PM

Why not a solid state relay?

Title: Re: 4-20 mA AC output
Post by: MrPike on March 05, 2018, 10:18:25 PM

Thanks Seth, I had to step away from this for awhile to focus on other jobs.  I think you may be eluding to just switching AC circuits on or off with a solid state relay????  I'm looking more along the lines of controlling the AC output as an analog signal.  I want to do this so I can simulate loading and unloading via the CT inputs to a power meter with a PLC.  I'm open to any ideas, thanks.