Host Engineering Forum

General Category => Do-more CPUs and Do-more Designer Software => Topic started by: willpoll on September 17, 2014, 01:14:56 PM

Title: DoMore F2-04AD-1 loop break detection
Post by: willpoll on September 17, 2014, 01:14:56 PM

Hi all:

I'm trying to set up 4-20mA analog inputs on a DoMore DL205.  I have it working, but I'm not seeing anyway to detect that a current loop is open.  0mA reads 0, 4mA reads 1, 20mA read 4095.

Over a scale of 0-4095 is 1 enough of a difference to declare a loop fail/open?

The internal flags do not appear to go high even when I open the circuit, only if I remove power to the module.

Thanks in advance for the great help I'll receive  :)

-Will

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: willpoll on September 17, 2014, 01:17:04 PM

Also, I have some level transmitters that take the loop to 22.6mA to indicate an internal fault, is there a way to detect this?

Thanks, Will

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: Controls Guy on September 17, 2014, 01:44:31 PM

Using a voltage input module with shunt resistors across your 4-20 signals will solve both issues (at slight loss of resolution).   Use 400-450 ohms or so.

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: BobO on September 17, 2014, 03:40:01 PM

The X bit associated with each channel should indicate broken transmitter, and I believe the WX value will be 0. That is not what you are seeing?

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: willpoll on September 17, 2014, 04:01:45 PM

WX0 value goes from 1 at 4mA to 0 at 3.997mA according to my loop calibrator. The X bit associated with this WX, X32 never goes on unless I remove the 24volt power from the F2-04AD-1 24+ terminal.  My thought is that it should go on when I open the loop but it does not.

This is a two-wire device, the AI module is powered from a 24v PS.

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Title: Re: DoMore F2-04AD-1 loop break detection
Post by: BobO on September 17, 2014, 04:07:24 PM

Quote from: willpoll on September 17, 2014, 04:01:45 PM

My thought is that it should go on when I open the loop but it does not.

It should...I think...and per our tests here, it appeared to. Odd thing is that the manual doesn't document it that way. To throw another wrench into the discussion, there have been mutliple versions of that module over the years, so the behaviors may even be different between versions.

I would love to offer more on this, but it isn't our module. Other than talking about how we handle it in our I/O driver, I really can't add much about how the module itself works.

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: willpoll on September 17, 2014, 04:23:45 PM

Thanks, I'll take this over to the AutomationDirect Forum.

-Will

Title: Re: DoMore F2-04AD-1 loop break detection
Post by: ADC Product Engineer on September 18, 2014, 11:07:44 AM

The F2-04AD-1 does not support broken transmitter.