Communication with Eurotherm 2408 via LabVIEW

[5211]

Hi there. I encounter a problem with my project. My project is to use LabVIEW Driver to make communication with Eurotherm 2408 temperature controller. The version of LabVIEW is 7.2. The driver is et24xx I downloaded from  http://www.eurotherm.co.uk/labview/ The serial port I am using is RS485/422 from UTEK Technology (Model UT-885). My problem is that even though i set all the values correctly (group unit , baud rate, and COM number on LabVIEW), The time out error message still pops up about 20 sec after I clicked the start buttom, which I assumed that the communication has failed.

I do check the wiring on Eurotherm 2408 and wiring on RS485/422 I am using but I am still failed to do the task.

Also, I am thinking if the issue is due to the incorrect serial port I am using. Is it really necessary for me to use the serial port from NI instead of using random brand serial port?

Can anyone give me a hand?

[Kyle_M]

5211,

Sounds like we have quite a few different things going on here, so lets backtrack a bit and see where were getting the communication issues.

First, can you find the card and complete a serial loopback test in MAX with the RS485 card? Instructions for that are here: 

http://zone.ni.com/devzone/cda/tut/p/id/3450

If that works, we can dive into the LV code and see whats going on there. 

Regards,

Kyle Mozdzyn

Applications Engineering

National Instruments

[5211]

Hi. Thanks for the reply
The loopback works well and the LabVIEW driver I am using is directly downloaded from NI website (et24xx) so it can be assumed that the problem is not on the code? The REM should flash when there is a connection however I cant get it flash so I assume the problem is in connection.

Also, just wonna make sure that whether the serial port I am using is compatible. Or should I buy the serial protect from NI?

[rolfk]

The Eurotherm controllers can be delivered with either RS-232 or RS-485 interface (it's a module that can be replaced inside the controller). Now I have a strong suspicion that the Eurotherm driver you downloaded was actually developed and tested with a controller with RS-232 interface.

I have had a few projects with the Eurotherm controller and a compactFieldpoint controller with LabVIEW, and initially we used the RS-485 solution. This was not possible to get working although I didn't have a chance to go very deep into debugging with this. The unit I got from the client to do some testing in our office appeared to be defect, and testing in the factory installation is a hassle. What did work is to replace the RS-485 interface in the controller with a RS-232 module and connect it to an RS-232 port on the compactFieldpoint. Another solution we also successfully used was to place an Eurotherm KD485 converter between the RS-232 interface on the computer and the RS-485 interface in the Eurotherm controller.

My suspicion is that the malfunction with direct RS-485 connection is due to the missing bias resistors on the compactRIO RS-485 interface (and also on the NI-USB-485 interface I had available to do some testing onsite). However time and other constraints did not allow us to debug that deep enough to make it work as a full RS-485 connection. Do a search on RS-485 bias resistor on the NI sites and you should get a document that explains about this. Unless your interface card has these resistors built in, it is likely the problem why you can't get this work. Some of the NI plugin boards do have programmable bias resistors that can even be switched on and off through a VISA attribute node if I'm not mistaken.

[Kyle_M]

5211,

Rolf makes some great suggestions.

Also, the et24xx driver maybe shouldn't be assumed to work. It is not an NI certified or supported driver, so we cant  guarantee it will be fully functional. We primarily host it for convenience. 

Regards,

Kyle Mozdzyn

Applications Engineering

National Instruments

[tadao93117]

I also spent quite a bit of time for setting up Eurotherm RS485 Comm.

I use USB-RS485 converter sold by U.S.Converter.com.

It uses Silicon Labs CP2102 chip and the terminal has T+, T-, R+, R-, GND.

The eurotherm has HD (GND), HE (A+), HF (B-).

I connected T+ and R+ together to HF(B-) and T- and R- together to HE(A-).

I found that terminal registor cause significant voltage drop, so I do not use any termial registor.

On software configuration, here is the list.

Func -- Modbus

Baud -- 9600

Delay -- no

Parity -- none

resolution -- Full

8 data bits

1 stop bit

flow control none

Timeout 1000msec

Block read 125

With this configuration, I made it work. I hope this information will help you make your system work

and avoid buying expensive KD485 ($569 quoted to me).