I haven't made RS-485 communications work

[jpmcgee]

(I've done RS-232 a lot, but I'm pretty clueless about 485 and about USB. I'm using magic spells that I don't understand.)

EKM Omnimeter I v3, S/N 000000013480.
USB to RS-485 adapter, purchased from EKM about a month ago.
EKM Dash v 503, downloaded earlier today.
Running on a Mac, with the required drivers for the USB to RS-485, downloaded about 2 weeks ago.

I've tried several things. I always get the error message "No Response - Check RS485 Connections".

Here's my setup:
From the computer, I've got a USB extender cable to the USB to RS-485 adapter. I'm pretty sure that works because the program says "No Response - Check RS485 Connections" when it's plugged in and "Bad Connection to USB or RS-232 Converter" when it isn't.

The RS-485 side of the adapter has 4 connections: +5v, B-, A+, GND. I've got a 720 Ω resister between +5 and B-, a 120 Ω between B- and A+, and another 720 Ω between A+ and GND. (I also tried it without the resistors.)

With the USB plugged in but the program not running, I get +4.96 v between +5 and GND. I get +3.451 between A+ and GND, and +3.547 between B- and GND.

The GND connects to the uninsulated ground wire in the cable to the meter. A+ goes to red, and B- goes to black.

The cable is 2-pair with a ground for each pair and a separate shield around both. It's 75' long and purchased new. I'm using 1 pair and its ground. The shield is not connected at either end.

At the meter end, the red goes to 11 (T+), black to 12 (T-) and uninsulated to 13 (ground).

There's a 120 Ω resister between 11 and 12.

In "EKM Dash", I entered the meter number, "13480". I also entered it as "000000013480", but the leading zeros got dropped by Dash.


Any suggestions on what different magic spells I can try? Or even better, any suggestions on how to understand better what's happening so I actually diagnose the problem?

Thanks,
Pat

[Jameson]

Hello Pat,

Welcome to the forum.

It looks like you have a pretty good understanding of RS845 to me

First I would just connect your RS485 wires up without terminating resistors or biasing resistors. I would not even use ground. Just RS485 A on the meter to A on the USB converter, B on the meter to B on the USB converter.

If you cannot get a good read from meter 13480 I would first try "Discover".

Sometimes our meters will be set to a meter number that does not match up to the number that is laser etched onto the face of the meter under the LCD screen. In this case you can "Discover" the actual meter number. Connect only one meter to your communication converter (USB, or iSerial). Then go to the Dash, select Edit Meter > Advanced then click "Discover" this will send a generic request and the meter will respond with it's programmed serial number. For example it might respond with 13490, but your meter is marked with a 13480. You can change the meter number to 13480 and then click "Set" (password "0"). This will set your meter to the correct value (13480 in this example case).

Another helpful tool in the EKM Dash is the Hex Inspector under the Help menu item. Click on the meter you are communicating with to see it's data. Then try to read the meter and see what data you are getting back.

Let us know how this works for you.

Regards,

[jpmcgee]

Hi Jameson,

Thanks for the quick reply.

OK. Where's "Discover"? I don't see it in my copy of Dash.

Pat

[Jameson]

Once you have a meter entered into the Dash, go to "Edit Meter" then click on the "Advanced" tab. The "Discover" button should be towards the top.

With just 1 meter connected to the USB converter over RS485, click "Discover" this should read your meter and the meter will respond with the number it is set to internally.

Thanks,

[jpmcgee]

Found it. It says "Please Wait. Communicating With Meter...". That message didn't change in the 10 minutes I waited. (I had to force-quit the app.)

I removed the resistors. This time it said "Please Wait (etc)" for a few seconds, followed by "Unable to discover the meter number. Please try again."

Thanks,
Pat

[Jameson]

In this case we will have to look at how you have the EKM Dash configured and how you have the meter connected to the USB converter.

If you can email us photos of your installation that would be the best.

Also in the EKM Dash, please go to Help > Send Diagnostic Information. This will email us your settings. An alternative to this would be to email us screenshots of the Meter Setup window in the EKM Dash.

Did you happen to do the 'Discover' with the Hex Inspector window open?

Thanks, we will get you sorted out.

[jpmcgee]

OK, I tried several things:

1) I did a continuity check on the cable. It passed. It was new, so I didn't really think it wouldn't, but I realized that I hadn't actually checked it before now.

2) I did "Send Diagnostic Information" in Dash. I added a comment to direct it to your attention.

3) I removed all the resistors at one end. I realized that when I tried it before, I hadn't removed all of them. Anyway, with just two connections to the cable and no pull-up/down or terminator resistors, it still didn't work.

4) I opened the Hex Inspector window before trying stuff. It showed the expected stuff (attached below) for send but nothing at all for received data. (Neat feature, thanks. I had tried to open it when I already had the Edit Meter panel open. I finally realized I had to open the hex inspector window first.)

5) I took pictures of my installation. They're at [http://xorandor.com/EKM/]. If it isn't clear from the pictures, all of the resistors at the USB end are connected only at one end and the ground wire from the cable is disconnected. Click on any thumbnail to get the larger picture.
--
(Data from Hex Inspector window:)
Send
2F 3F 30 30 30 30 30 30 30 31 33 34 38 30 21 0D
0A

Send
2F 3F 30 30 30 30 30 30 30 31 33 34 38 30 21 0D
0A

Send
2F 3F 30 30 30 30 30 30 30 31 33 34 38 30 21 0D
0A

Send
01 42 30 03 75

Send
2F 3F 30 30 30 30 30 30 30 31 33 34 38 30 21 0D
0A

Send
01 42 30 03 75

Send
2F 3F 39 39 39 39 39 39 39 39 39 39 39 39 21 0D
0A

Send
01 42 30 03 75

Send
2F 3F 39 39 39 39 39 39 39 39 39 39 39 39 21 0D
0A

Send
01 42 30 03 75

Send
2F 3F 39 39 39 39 39 39 39 39 39 39 39 39 21 0D
0A

Send
01 42 30 03 75

[Jameson]

Thank you for the data and for the photos.

Your system is acting as though the meter is not connected at all. I cannot see from your photos where you have the RS485 data wire connected to the meter. It looks like your Red wire is RS485 A+, where do you have this connected? Please double check your connections.

When connecting the data wire it is best to back the terminal block screw all the way out and then insert your wire. Then tighten the screw.

One thing to be aware of:

You have your CT wires connected to the meter White, Black, White, Black from left to right. It should be Black, White, Black, White from left to right.

Thanks for your patience.

[jpmcgee]

Hi Jameson,
Success at last!

I did have the RS-485 wires connected to the meter incorrectly.

It took me a while to figure out why I made that mistake. On the bottom row of the meter, the connections are numbered 1-10, with 1 on the left. On the top row, the connections are numbered 11-16, with 11 on the RIGHT. I had wired things as if 11 was on the left, similarly to the direction in which they are defined on the bottom row. I still have a hard time wrapping my mind around the concept of having two parallel rows of connections with the numbers going in opposite directions. It didn't help that the hookup sheet didn't have a diagram of this connection.

I also just now switched the CT wires around. When I hooked them up the first time, the diagram didn't specify which color went to which connection. So I just hooked them up randomly. I see now that this is mentioned in the text. Since so much of the information in the text is just duplicated from the diagram, I didn't read the whole text.

Thanks very much for your patience with me.

Pat

[Jameson]

Pat,

Not a problem at all. All's well that ends well.

Glad you got it sorted out. Let us know if you need anything at all.