Compair air compressor on Modbus RTU - How to?

[danw]

You have working Modbus slaves. Can you connect from your PC (running a Modbus master program) through the 232/485 converter and read a value from a register on one of your previous Modbus slaves, proving the PC, client program, converter, and wiring?

You know the comm setup for drive slaves. It is ? 9600 8N1?

Are your pre-existing slaves running the same comm settings?

When you added the drive slaves to the wiring network, are they added without spurs, but daisy chained in multidrop fashion?

When you get response, is that no response from the PC/converter/single slave or with other devices on the network?

Are there terminating resistors on the network A or B lines?

 

[rguimond]

Yes, I can see the existing slaves and collect data from them using various modbus "sniffers".

Current network setting is 19200, 8N1. I've tried every possible combination.

Terminating resistors on both ends of daisy-chained network. To rule out network trouble, I even tried connecting the converter right to the compressor with a 6' long piece of twisted-pair (with and without terminating resistor). I don't even see traffic indicator on the converter, but I do if I connect the converter to the "working" rs-485 network.

Im at a point now where I'm seriously doubting that ModBus communication is even possible with the controller, even though the literature states it is and the on-screen configuration allows changing of the baud rate and slave address.

 

[danw]

Your suspicion that there's no Modbus firmware might be correct.

However, there are so possibilities if it's there.

Modbus RTU must be 8 bits. You can set the baud rate.

Parity is questionable. If it's odd or even parity it has to be one stop bit. If it's no parity it could be 1 or 2 stop bits. It is quite rare to encounter 2 stop bits.

The functionality of the A & B RS-485 lines can be reversed, even if they are marked. Phoenix Contact's converter is marked the opposite of their industrial wireless radios - two divisions withina company interpret A & B differently.

But with a known working Modbus master PC program and a converter, you can try the following matrix to confirm it does nothing.

A & B in the current wiring:
even parity
odd parity
no parity, 2 stop bits (if you can)
no parity, 1 stop bit

A & B reversed from current wiring:
even parity
odd parity
no parity, 2 stop bits (if you can)
no parity, 1 stop bit

The terminating resistors can load the circuit. For a short run directly to the drive with a PC (nothing else on the comm link), I'd try it without the terminating resistor(s), just to see if you get connection

 

[Mickey]

Are you sure its Modbus RTU and not Modbus ASCII?

 

[danw]

Compair's documentation has been somewhat "sketchy".

The statement that it was Modbus RTU was made in the first post. Good point, though, is that confirmable?

 

[rguimond]

Your suspicion that there's no Modbus firmware might be correct.

However, there are so possibilities if it's there.

Modbus RTU must be 8 bits. You can set the baud rate.

Parity is questionable. If it's odd or even parity it has to be one stop bit. If it's no parity it could be 1 or 2 stop bits. It is quite rare to encounter 2 stop bits.

The functionality of the A & B RS-485 lines can be reversed, even if they are marked. Phoenix Contact's converter is marked the opposite of their industrial wireless radios - two divisions withina company interpret A & B differently.

But with a known working Modbus master PC program and a converter, you can try the following matrix to confirm it does nothing.

A & B in the current wiring:
even parity
odd parity
no parity, 2 stop bits (if you can)
no parity, 1 stop bit

A & B reversed from current wiring:
even parity
odd parity
no parity, 2 stop bits (if you can)
no parity, 1 stop bit

The terminating resistors can load the circuit. For a short run directly to the drive with a PC (nothing else on the comm link), I'd try it without the terminating resistor(s), just to see if you get connection

Thanks, but I already tried every possible combination of baud rate, parity, stop bits, resistor on one end, resistor on both ends, no resistors, etc.

 

[rguimond]

Are you sure its Modbus RTU and not Modbus ASCII?

Documentation clearly states "ModBus RTU". See attached.

 

[Mickey]

So it does. How about error checking the PDF you posted says "CRC". The ML1100 can be "CRC" or "BCC". The working devices and your Modbus software are set to??

 

[robertkjonesjr]

Probably a couple of stupid questions:

You couldn't determine the pinout for your unit early on - but I saw pinout information in the pdf link you provided. So was it an oversight, or is the pinout information for different hardware listed and you had to ask the vendor for your particular hardware?

Related question - a lot of the items I buy for our plants have modbus as an option. We have ovens and chiller control systems that have communication options - they always cost a lot and no one ever looks at the options but me... so just a thought - is Modbus an option here, and if so, was it ordered and installed? Many times the connector is absent when the option is not there, so this is a long shot but might be worth verifying because you have a connector. It looks like you have tried everything else.

Also another long shot - are you using a PC with real serial port? Sometimes USB to serial adapters are flaky. At the very least, you could verify the send request from the PC and conclusively isolate the device as the problem. No LED indication at all means your not sending - right? So if this PC setup works elsewhere, sounds like a physical layer issue between the serial ports.

 

[danw]

from the manual:
1) Character Frame: 1 Startbit / 8 Databits / 1 Stopbit
defines this comm setup as a "no parity" character frame
2) handles only 03 commands (4xxxx Holding registers)
3) registers:
0004h final pressure ( 1/10 bar ) [Byte]
0005h line pressure ( 1/10 bar ) [Byte]
where [Byte] = 8 bit / UNSIGNED;

If you can't read a value from register 40005 or 40004 with command 03h on slave 3 at a baud rate that matches on the PC and the drive, with the PC COM port set for no parity, then something's missing or broken on the drive.

 

[rguimond]

So it does. How about error checking the PDF you posted says "CRC". The ML1100 can be "CRC" or "BCC". The working devices and your Modbus software are set to??

Regardless of what error checking was set to (I've tried both), I should still see indication of network traffic on the converter.

 

[rguimond]

Probably a couple of stupid questions:

You couldn't determine the pinout for your unit early on - but I saw pinout information in the pdf link you provided. So was it an oversight, or is the pinout information for different hardware listed and you had to ask the vendor for your particular hardware?

Related question - a lot of the items I buy for our plants have modbus as an option. We have ovens and chiller control systems that have communication options - they always cost a lot and no one ever looks at the options but me... so just a thought - is Modbus an option here, and if so, was it ordered and installed? Many times the connector is absent when the option is not there, so this is a long shot but might be worth verifying because you have a connector. It looks like you have tried everything else.

Also another long shot - are you using a PC with real serial port? Sometimes USB to serial adapters are flaky. At the very least, you could verify the send request from the PC and conclusively isolate the device as the problem. No LED indication at all means your not sending - right? So if this PC setup works elsewhere, sounds like a physical layer issue between the serial ports.

Yeah, I overlooked the pinout part before the first post.

Manufacturer claims Modbus is present, and the setup screen on the compressor indicates it is, too.

Using real serial port. I can (read & write) to/from modbus devices on the network, just not the compressors. Tried putting compressors on their own physical network (see previous posts) - no luck.

 

[leyva_9ap3d]

i have a big problem¡

Someone's gotto know how to accomplish this. I'm beating my head against a brick wall waiting for replies from Compair (US & Canada - even tried South Africa). Everyone I speak to seems to "know" this is possible, and promises to get back to me with the info, but never does. Frustrating.

Basically, the L45SR compressors I have are networkable on a Modbus RTU network. My problem is that I have no idea where to connect the twisted pair (I'm guessing it's at the 3-pin Phoenix connector at the back of the Delcos 3100 controller). Of course, I'm not overly eager to just blindly connect the cable and give it a try.

My second problem is that, even if I figure out how to physically connect the controllers to the network, I have no way to configure each with a unique slave address or to determine what memory address serves what function.

A bit of guidance would be appreciated!

hi¡ guys, i have no idea what are you talking about.....
i have a delcos 3100 electronic controller and someone expert decide to burnout (it was conncted and a 220 peak voltage came on and damage the supply section. we repair it but it doesn't display anything..... could you help and send me something about the wiring diagram or something to comunicate with the card.

 

[sthompson]

Leyva:

Start a new thread with a helpful title. In the post put in as much pertinent data as you can. Exact model numbers, exact problem, and specific questions. You are much more likely to get an answer that way. Appending to someone elses old thread will limit how many see it.

Stu.....

 

[327jwolf]

Have you double checked the msg settings in the ml1100? I have a simular problem and it ended up I had one msg setup wrong? Just a thought.