RS485 Bad Connection

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kennycaldas
Posts: 4
Joined: Wed Jun 18, 2014 8:58 am

RS485 Bad Connection

Post by kennycaldas »

Hello,

I recently got one EKM Metering for me, the I v.3
I already had a USB to RS 485 converter, which I believe use the same technology from yours:

http://www.ftdichip.com/Support/Documen ... CABLES.pdf

Says in the datasheet thar:

Orange Data+(A) Bi-Direction Data + (A) Signal
Yellow Data-(B) Bi-Direction Data - (B) Signal

I download the EKM Dash trial to test the readings, but I couldn't get the communication working
It keeps saying that I have a "Bad Connection" or "No Response"
I attached the pictures of the errors and how I connected the wires on meter.
Any ideas why is it not working?

Thanks!

Dash:
EKM Dash reading
EKM Dash reading
ekm test.JPG (73.5 KiB) Viewed 9139 times
Connections:
Connections
Connections
20140618_104937.jpg (145.61 KiB) Viewed 9139 times
Jameson
Posts: 860
Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA
Contact:

Re: RS485 Bad Connection

Post by Jameson »

Hello kennycaldas,

Thanks for posting your question to our forum.

The message you are getting in the EKM Dash indicates that the Dash (your PC) is not able to connect to your third party USB converter. The Dash is converter model agnostic, but because it is not one of ours I would not be able to say why your USB converter is working or not. Please make sure you have your EKM Dash pointed to the correct port (on a PC this could be COM1 to COM24 or more). To check this on a windows PC I believe it is under Control Panel > System > Hardware > Device Manager > COM Ports

So the issue is not the connection from the USB converter to the meter, it is the connection from your PC to the USB converter.

And as a heads up, third party USB converters tend to give us a lot of headaches surrounding the communications from the USB converter to the meter as well. We use terminating resistor values and biasing resistor values in our USB converters that give them optimal communications with our products.

Hope this helps,
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371
kennycaldas
Posts: 4
Joined: Wed Jun 18, 2014 8:58 am

Re: RS485 Bad Connection

Post by kennycaldas »

Hi Jameson,

Thanks for replying,

So, I checked the COM ports; they are ok.
I tried to use some resistors, biasing and termination.
I only have 350Ohm with me right now,, so I did something like this:

2x 350Ohm (=700Ohm) series connected from B- to +5
2x 350Ohm (=700Ohm) series connected from A+ to GND
2x 350Ohm (=175Ohm) parallel connected between A+ and B-

But now what is showing is " Bad Meter Read Data "

Am I using the resistors correctly? Do you have any suggestions on which value for these resistors I should use?

Thank you!
Jameson
Posts: 860
Joined: Fri Nov 04, 2011 7:42 pm
Location: Santa Cruz, CA
Contact:

Re: RS485 Bad Connection

Post by Jameson »

Seeing as you are using a 3rd party USB converter, Im afraid this will take some experimentation on your part. Just keep changing values until you get 100% reliable communications.

B- to +5 (this is a biasing resistor) we use one 470 ohm

A+ to GND (this is a biasing resistor) we use one 470 ohm

A+ and B- (this is the terminating resistor). We usually leave this off. This only comes into play when you have really long runs (over a couple thousand feet) or a lot of meters.

Hope this helps.
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371
kennycaldas
Posts: 4
Joined: Wed Jun 18, 2014 8:58 am

Re: RS485 Bad Connection

Post by kennycaldas »

HI Jameson,

Thanks for the tips, the cable is now working!

Kenny
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