Compair air compressor on Modbus RTU - How to?

[rguimond]

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!

 

[danw]

If the 3 pin connector is the 'networking' connection, it's probably RS-485: A, B and a ground. An ohmmeter will probably tell you which of the 3 is the ground.

Telling which is A or which is B is a flip of a coin; the EIA-485 standard doesn't even define which is which, so most people try it one way and if it doesn't work, swap the two.

The comm parameters are not usually setup via the network link, they're usually setup in a configuration menu , buried somewhere at the end of all the other menu items.

Not knowing what register is what variable and in what format is also a problem.

You can always read the registers as integers or floats and see if any of the numbers makes sense, but you'd have to be more adventuresome than I to bother.

Have you googled for a manual that has the Modbus map and comm setup parameters?

 

[danw]

Unless updates or options differ from the publicly available information, you're out of luck. No Modbus. Proprietary serial protocol

page 72, User Manual L45SR:

1.6 RS485 Communications
The SureScan control unit is compatible with the
electrical RS485 communications standard. The
communication parameters are:

9600 baud, 8 data bits, no parity and 1 stop bit.

The message protocol is a proprietary multimaster
protocol compatible with the SmartAir Air Systems
Control Units and with the Active Network Interface
for connection to PCs etc.

http://87.243.193.82/ <> stationary screw > L45SR

 

[rguimond]

Unless updates or options differ from the publicly available information, you're out of luck. No Modbus. Proprietary serial protocol

page 72, User Manual L45SR:

1.6 RS485 Communications
The SureScan control unit is compatible with the
electrical RS485 communications standard. The
communication parameters are:

9600 baud, 8 data bits, no parity and 1 stop bit.

The message protocol is a proprietary multimaster
protocol compatible with the SmartAir Air Systems
Control Units and with the Active Network Interface
for connection to PCs etc.

http://87.243.193.82/ <> stationary screw > L45SR

Thanks, but this information is outdated:

I finally received a reply from a factory rep. today. He sent me a Programmer Guide for MODBUS-RTU Delcos 3100. At least now I know the memory addresses for holding registers.

Now it's just a matter of determining where the two-wire network connects to the controller. Strangely, the physical connection information isn't in the Programmer Guide. I'm tempted to try the 3-pin Phoenix connector... Hopefully the rep. replies with the connection diagram before I jump blindly into this!

 

[rguimond]

I have determined the pinout for the network - #14=RS485+, #15=RS485-, #16=GND.

Ran 2 twisted pair cables to the compressor, broke an existing cable and connected them at both ends. Tested communications to devices originally on the network and all are OK. Can't get controllers to reply to MSG from ML1100. Other devices work fine.

I've tried 4800, 9600 & 19200 baud; ODD, EVEN & NO parity; switched polarity of data wires at every baud/parity setting - no luck.

Any suggestions? Should I be able to connect directly to the Modbus network through a serial port on my laptop, or do I need an adapter? I suspect there's a free modbus communication diagnostics application somewhere...

 

[robertkjonesjr]

You'll need an adapter, and I think your approach is correct - be able to see it with a laptop first. I usually connect with a PC first to verify all wiring, serial port settings, registers, and data formats. I add the info to the documentation, then I move to the final control system (plc or whatever). That way most settings are correct, and it helps with troubleshooting by eliminating as much uncertainty as possible from the field connection.

I use this to start. If I have trouble with noise and other such things like blowing fuses and the like, I switch to this to connect.

There is plenty of free software to connect:

http://chipkin.com/cas-modbus-rtu-parser
www.azeotech.com (comes with free modbus utility as part of demo)
Kepware OPC server has a two hour demo limit, so can use to test
Redlion Crimson software Modbus driver works with the built-in emulator on a pc
http://modbus.pl/MTester.htm
And many more from google...

 

[danw]

I agree with Robert's points.

I always establish communications first with a Modbus Master on the PC, then move to whatever the other Modbus master is ( I use Modscan32 for a generic PC master).

The PC's COM port is serial RS-232. You'll need an RS-232/485 adapter to for the physical serial link to operate properly with the RS-485 on the compressor controller. I use the B&B's as well. However, I have found that the port powered unit might not work on some laptops, because laptops limit power to the serial port (if they still have a serial port) so I use a 12Vdc power supply with the B&B port powered model to ensure that the converter doesn't fail due to lack of sufficient power.

Since you now have the slave register map, you can attempt to read some value that (pressure?) that you can confirm elsewhere (pressure gauge?) from wherever the map tells you the value is at, like a 4xxxx register. If they don't tell you the format, then assume integer first.

The factory documentation had specs for the comm link: 9600 8-N-1 for their proprietary protocol. Are you sure you can't weasel the default comm link specs out of them for the Modbus? I'd probably start with 9600 8-N-1 or 19.2K 8-N-1 if otherwise unknown.

Being Modbus RTU it will NOT be 7 bit (7 bit is Modbus ASCII).

 

[rguimond]

Thanks for the assistance so far.

I have an Allen-Bradley 1761-NET-AIC. I know the manufacturer's literature doesn't specifically state that it will work with and RS-485 based network, but it doesn indicate that it's a RS-485 to RS-232 isolator. Do you think it might be worth trying?

 

[danw]

The 1762-NET-AIC definitely has an RS-485 port on it. See page 9 (pdf)

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1761-um004_-en-p.pdf

I'm not familiar with it, but it appears from a quick read that it is a combination RS-232/485 converter/isolator.

A very big question remains: can whatever controller you are connecting this module to function as a Modbus Master? The compressor is a Modbus slave and is silent until it is "spoken to".

 

[Mickey]

The

A very big question remains: can whatever controller you are connecting this module to function as a Modbus Master? The compressor is a Modbus slave and is silent until it is "spoken to".

I believe the OP said he had a ML1100 if so then see PDF below.
It should work.

 

[rguimond]

I believe the OP said he had a ML1100 if so then see PDF below.
It should work.

That's right. I already use the ML1100 as Modbus Master for two temperature controllers (Slave 1 & 2). The compresors are configured as Slaves 3 & 4.

I'll try using the NET-AIC module on Tuesday to see if I can establish comms that way. I already know the network is working becuase of the successful reads from the temperature controllers, so it should be easy to connect with my laptop using Chipkin modbus scanner.

 

[rguimond]

Update

1761-NET-AIC will NOT work as a RS-232 X RS-485 network adapter for this application. Not sure why - it just won't. I have proper adapter from B B - Elec on order.

 

[rguimond]

I purchases a proper RS-232 x RS-485 converter and tried it today. Worked like a charm on our existing Modbus network, but no luck on the Compair compressors. Getting really frustrated...

 

[danw]

You configured the compressors as slaves 3 & 4 in the uLogix, right? Did you configure the compressor slave node ID's?

 

[rguimond]

You configured the compressors as slaves 3 & 4 in the uLogix, right? Did you configure the compressor slave node ID's?

Yes to both questions. I don't even get indication of network traffic on the RS232 x RS485 converter.