20mA current loop serial data communication ? 4

[HannAri]

Hi,
I need to extend an old 20mA current loop (serial data communication). I have an rs232 to CL converter that does not have an external power supply. This works fine for short distances but now I have moved the machine and it has stopped working. The wire I am trying to run it through is about 200m (650ft.) and is about 8ohms back and forth.
The current loop has 3 wirers: IN, OUT and a 0 (Zero).

I rely need a solution to fix this, any ideas?

Thanks

 

[IRstuff]

Your data rate is probably too high for the distance

TTFN
faq731-376

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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[itsmoked]

How does a "loop" have three wires??

Keith Cress
kcress -

http://www.flaminsystems.com

 

[HannAri]

itsmoked, It is two loops with one common. (full duplex)

 

[HannAri]

I think...

 

[VEBill]

How about extending it with fiber optics?

http://www.lab-systems.com/products/fib-opt/afl300/

 

[robertjo24]

RS-232 current loop converters generally have 4 wires (TX+&-, and RX +&-), not three. Is it possible that in your configuration, the - lead from botht the TX & RX lines were tied together? What type of converter are you using?
When links are not properly configured, they will often work over short distances, but not longer ones.
Is it possible to get 4 wires for your link?
Also, for the longer distance I would get a powered device. B&B makes great converters.

http://www.bb-elec.com/Products/Datasheets/232CLDR_3713ds.pdf

 

[SteveWag]

Let’s step back and more clearly define the problem.
What is the process measuring device, how many wires connect that device to the converter? Did the measuring device to converter distance change or did the converter move with the device? Of the three mentioned terminals, are they connected to the device, just two or are all three used? Describe the RS232 connections, or alternately, at the other end of the 232 link. Is the converter recognized? It would help if you could identify the make and model of both the process device and the converter.
Maybe you could be helped if the problem is more clearly described
Steve

 

[HannAri]

The machine is an old Icelandic weighing scale called POLS FL-185-D2, since the early 90´s. The converter is also from them and is called EL-0e. So I do not think that any of you know it.

But regarding the 3 wires on the CL, from what i was told is that the 0 (zero) is a combination of the Tx- and Rx-. The other two IN and OUT are the Tx+ and Rx+.

I put a few pictures of the converter. The distance from the Pc to the converter is about 1m (3ft) and the distance fro the converter to the grader is about 200m (650ft). The cable i am running it over is a CAT5 where i use 3 of the pairs. I.e. I use one pear together for the IN, one pair for OUT and one pair for 0.

One thing i am wondering cold it be that i need a better cable?

Thanks a get for taking the time to help me.

 

[SteveWag]

You may try switching your pins 2 and 3 at one end only. You want RD connected to TD and vise a versa. I can’t tell if your setup as DTE to DCE or DTE to DTE. Check the wiring for Null Cable and Straight through Cable.
Steve

 

[Compositepro]

By using twisted pairs of wire as a single wire you lose the benefit of twisted pairs, which are less cross-talk and interference.

 

[djs]

I would recommend using high quality twisted shield pair cable. The conductors need to be as large as you can get them, at least #16 AWG. Use two cables, one for each current loop. At the scale side one conductor of each cable will be connected to the common. At the PC converter side keep the conductors separate. Also use a powered converter at both ends.