Compax3 servo and ML1100 serial comm

Hi,



I need some input to a system that I’m altering at the moment.



I have a machine that is now using a servo drive instead of pneumatic cylinders. The servo is a Compax3 with RS485 communication port and my PLC is a MicroLogix 1100.



Originally what we intended was to use Modbus communication protocol but it turns out the servo speaks ASCII and the PLC RTU type Modbus, according to Wikipedia the two types are not compatible.



Since the PLC doesn’t speak plain RS485, but rather the Rockwell variant DH485 they can’t communicate directly that way either.



So we found a RS232 to RS485 converter on a dusty shelf and we are now able to send a command to the servo, and it answers back with the correct value (the position of the servo). However, this value we see only in hyperterminal not on the PLC.



I use the AWA instruction to send the command to the servo, but no matter what command I use to try to read the answer it will fail with the error code 09h. This is something with the device not being DH+ or DH485 compatible (sorry I’m at my home computer at the moment and I haven’t got RSLogix500 installed here), but CH0 is configured to DF1 Full Duplex and therefore I’m confused about this error.



Does anyone have experience with this combination of products or similar systems? I would be grateful for any hints and examples you might have.



Best regards,



Michal Rudbeck-Rønne

M2R

I'm not totally sure if I understand your problem. I am at work today and we are installing a message sign connected to a ML1100 using ASCII protocol. I simply selected ASCII as the protocol and now I have an RS232 connection with the sign.

I posted a question on this forum a few days ago about being able to transmit out of the ML1100 using an RS-485 connection. The Rockwell literature makes frequent mention of the ML110 be able to transmit rs485, but I have not had any luck doing so.

My thinking is that you should be able to use cable # 1763-nc01 to do RS-485 - but I have not had any luck - the problem could be the sign.

The way that I connected between the the sign and the plc (using RS232) was to "butcher" a 1763-PM02 cable.

We did try the ASCII setting for CH0 but that didn't work either.


And the 1763-NC01 is also what I tried using at first, but also with no luck.

Michal

Self inflicted wounds

Michal_dk said:

Originally what we intended was to use Modbus communication protocol but it turns out the servo speaks ASCII and the PLC RTU type Modbus, according to Wikipedia the two types are not compatible.

Click to expand...

There is no easy solution to make your system work. I would have made sure the drive can communicate with the ML1100 before buying it. The cheapest thing to do is to replace the drive with one that can communicate with a ML1100. How many drives are there? The drives can't be the expensive if the motor and drive were used to replace a pneumatic system.

I'm a newbie to AB plc communications, so take everything I say with a grain of salt. It sounds like you got your rs232 to work by selecting DF1 communications and using thev AWA instuction to send your commands. Apparently this setup works when talking from the plc to the drive, but not vice versa.

Did you set the terminations characters on the channel 0 comms setup? According to the AB literature, ascii communications is terminated with certain characters and those character need to specified.

I got a sneaking suspicion that your setup won't work, and will never work, because you are configured for df1 protocol. My guess is that you are going to have to have ascii protocol selected in order for your read instructions to work or else you are going to get that error whenever you try and do a read.

Your post has me wondering if I configured my channel 0 for DH485 andused the AW or AWA instruction if the message from my plc to the drive would be sent in ascii format via rs485. In my case, I do not recieve any data from the sign, so I don't do any ascii reads.

Keep us updated on what you find out.

Hi Guys,


PN: YES it would make sense to replace the drive with an AB compatible one, perhaps even an AB drive ;-) Unfortunately I got into this mess thru the local Parker Hannifin sales office, so I'm not about to try to sell the end customer an AB drive.
I did talk to AB and they have in fact offered the customer a very good deal on an AB solution, why they havent choosen it is still a mystery.

EB: This morning I switched to ASCII on the controller, and now I can at least read between the PLC and Hyperterminal.
But now I don't get a responce from the drive :-(

I'm hoping that the Parker technician will drop by on his way home, he has a "sniffer" for RS485 and then we'll be able to see what the drive recieves.

I'll keep you posted.

Michal

Hi Michal,

Do you have any software that communicates with the drive?
How you do the parametrization?

If you have one that talks to your 485 port either you sniff on 485 either you sniff on PC on RS232 side. From my point of view better on RS232 as the PLC is seeing same.

So sniff/monitor the RS232 side while you are comunicating with the drive with his own software and you will see what he wants.

Then make the appropiate ASCII conversion inside the ML1100.

However it will be a PITA to do conversion in ladder.

I proved myself right once doing exactly this, showing you can do ASCII comm between a SLC plc and Indramat servo, when everybody else was saying it is not possible, but in the end cost the SLC guys more than one week to do the proper conversion.

So it might me a sensible approach just to change the drive.

Hi,


yes I can see "inside" the drive with the Compax software, but I use a sniffer on both the 485 and 232 side.

Funny enough, today I got the comm working from PLC to drive and from drive to converter. But on the RS232 side of the converter the data is gibberish, and this is with the 1761-Net-Aic and with a Noname converter too.

So what I'm going to do tomorrow is try to somehow get my hands on an analog output module and send the two values for force to the drive that way and similarly use an analog input to convey the position of the drive to the PLC.

This is because I have to have the machine out and running by monday, and we have to do something ASAP.

Then we'll have some time to figure out what we can do to make this work the proper way.

But any input will still be apreciated, so keep them comming please!

Michal

Gibberish on RS232 side beats me.

Actually I used converters only for Modbus, never for ASCII, and it worked straight away.

And all RS232 sniffing on ASCII gave me plain and nice ASCII characters.

The analog way will be ok only for a couple of parameters.

Also looks like you are in badluck with the Compax3 models, as on a quick look I can see that on X10 connector they claim they have either RS232 either RS485 depending if you put 5V on pin1.

When you will work out a solution please tell us how you did it.

Hi again!


Well We did solve the problem!

The Compax3 is configured to RS485 and the ML110 to RS232.

Then the critical part (for me anyway) the right converter! We used a M485-CNV232-I bought from DANBIT in denmark.

Now there is no gibberish any more.

I will try to attach some schematics on how we configured the cabling.

Another thing that is crucial is how the PLC reads the data on the com port - I had to hire another guy to do that for me :-(
But to make a long story short, you need to make sure that you only read if the Copmax3 is finished writing!

I had my reservations if this would be fast enough, but we haven't had any problems yet.

Regards,

Michal_dk