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Author Topic: BRX analog output problem  (Read 16742 times)

Watermark_JS

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BRX analog output problem
« on: October 17, 2020, 01:09:17 PM »
I could really use some help with this.  I am on-site, 1,000 miles from home, and my customer is waiting for me to resolve this issue.  I was on the phone with A/D tech support multiple times yesterday and got nowhere. 

I have a BX-DM1E-10ED23-D that is sending 19.2mA from WY0 when there is a value of 6553 in the output register.  It should measure 4.0mA.  A value of 32767 yields 31.7mA. :o

This has been verified with multiple meters and I have connected several different devices to be sure the field device isn't causing this.  I have attached a table that shows measured mA at various output values.

To eliminate wiring or interference issues, I removed the PLC from the enclosure and have it sitting on a desk, powered from a different 24VDC supply.  The analog output is the only I/O wired at this time.  I also cleared all of the PLC memory and re-flashed the firmware.  This had no impact on the results.  Normally, I would just RMA the unit, thinking there is something wrong with the analog output...

HOWEVER, I when I attach a BX-4AD4DA-3 analog combo card, all of its outputs exhibit the exact same behavior!  Could the problem just be the CPU?  Is it capable of causing the add-on module to do this? ???

Best case, I get A/D to overnight a CPU for arrival Tuesday.  I need to be confident that it will solve the problem, as the customer is waiting. :'(

Any ideas would be appreciated.
« Last Edit: October 17, 2020, 01:26:28 PM by Watermark_JS »
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RBPLC

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Re: BRX analog output problem
« Reply #1 on: October 17, 2020, 01:58:32 PM »
Can you post a picture of your setup including PLC, meter and wiring? Also a picture of the configuration settings in the Analog I/O section of the controller.
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BobO

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Re: BRX analog output problem
« Reply #2 on: October 17, 2020, 02:00:39 PM »
No, the CPU can't cause the module to misbehave in the same way. Leads me to believe something is wired wrong, or the measurements are being done wrong.
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Watermark_JS

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Re: BRX analog output problem
« Reply #3 on: October 17, 2020, 04:29:47 PM »
Sorry it took a bit to get this reply out.  Had to clean up wiring to get everything in one photo.

WX0 is scaled 0 - 100 at RX0 and is functioning as a stand-in for my field device and also as a secondary meter.

WY0 is scaled 0 - 100 at RY0 and is my sourcing analog out, wired to WX0.  My mA meter is on this wire.

The value in RX0 is pretty close to the % my meter is reading.  I couldn't get the high-res photo to upload, so there's a closeup of the data view and meter values in the next reply.

Thoughts?

« Last Edit: October 17, 2020, 04:36:41 PM by Watermark_JS »
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Watermark_JS

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Re: BRX analog output problem
« Reply #4 on: October 17, 2020, 04:34:41 PM »
Here's a closeup of the values.
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BobO

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Re: BRX analog output problem
« Reply #5 on: October 17, 2020, 04:41:06 PM »
I'm not sure about your wiring, but it looks like it is wired to the power supply. Pretty sure that's wrong.
« Last Edit: October 17, 2020, 04:48:23 PM by BobO »
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Watermark_JS

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Re: BRX analog output problem
« Reply #6 on: October 17, 2020, 04:48:51 PM »
1C on the CPU is connected to DC- on the power supply to make input WX0 sinking. 

1C on the combo module output section is connected to DC+ on the power supply to make those outputs sourcing.

Is that incorrect...?  I'm digging into the online manual now...
« Last Edit: October 17, 2020, 04:52:33 PM by Watermark_JS »
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BobO

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Re: BRX analog output problem
« Reply #7 on: October 17, 2020, 05:03:35 PM »
Quote from: Watermark_JS on October 17, 2020, 04:48:51 PM
1C on the CPU is connected to DC- on the power supply to make input WX0 sinking. 

1C on the combo module output section is connected to DC+ on the power supply to make those outputs sourcing.

Is that incorrect...?  I'm digging into the online manual now...

That is not correct.
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Watermark_JS

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Re: BRX analog output problem
« Reply #8 on: October 17, 2020, 05:10:53 PM »
Thanks BobO!  I tied the two commons together and it works.  That seemed very wrong.

So, does the combo card auto-detect whether it's sinking or sourcing somehow?  I'm not sure I get it.
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BobO

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Re: BRX analog output problem
« Reply #9 on: October 17, 2020, 05:18:17 PM »
It shouldn't be tied to the P/S at all. Commons are tied, input tied to output. There is no sinking or sourcing.
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Watermark_JS

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Re: BRX analog output problem
« Reply #10 on: October 17, 2020, 05:22:03 PM »
 :o  Mind blown.
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BobO

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Re: BRX analog output problem
« Reply #11 on: October 17, 2020, 05:29:28 PM »
Quote from: Watermark_JS on October 17, 2020, 05:22:03 PM
:o  Mind blown.

BRX internal and -3 analog are fully internally powered. It's a feature.  ;)
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