Eurotherm 2704 connection via serial port with ModBus

Question

Hello guys,
first some words about my problem:
I have to develop a software which allows reading and writing the
temperature (we have 3 Eurotherm 2704) (I think some of you know this problem yet ).
I wrote already the program and it works, but I used "iTools OPC
Server" for my program and it was the demo version (works only 30 minutes).
The group doesn't want to pay for the iTools, I should solve this problem without
iTools .
In this forum I found out, that I can use the ModBus for it:
http://forums.ni.com/ni/board/message?board.id=170&thread.id=468139&view=by_date_ascending&page=2
I know, there are some similar threads here, but I am new with LabView
and need some help.
I downloaded one example “my modbus serial query.vi “
http://forums.ni.com/ni/board/message?board.id=170&thread.id=135288&view=by_date_ascending&page=2
but it does not work (I am not really sure, what I have to change in the
file)
With OPC Server I found out:
COM5
Baud Rate 9600
Parity: None
Flow Control: None
Data Bits: 8(RTU) (I can choose RTU, but where can I change to 8 bit ?! )
And by other properties, I have no idea what I have to change there
For Example
Modbus Data Unit In (all read and write mode ? Which one do I need to read the temperature and to set the set temperature?)
Modbus Command ?!!!
No idea.
I have folowing adresses (comms address 0x00030001, canonical address: 1)
Which one do I need ?!
I think if I get the signal from one temperature controller, I can do it for
other, but my problem is now THIS one.
Can you help me whit it ?
Should I use a other example ?! Maybe do you know better one?
Thank you, very much.
Alexander

Answer 1

Hello Putnam and Christian,
I think the problem because you can not understand my question is my English, sorry
I'll try it again: 
@Christian:
Thank you for the links, but I think all threads in NI Forum with topic "Help, Eurotherm 2704 ?" were written by me
You understood my problem correctly.
We have 3 temperature controllers and I have to develop a LabView program, which allows reading the temperature from the controllers. It should be possible to write the set temperature from LabView to temperature controller as well.
The controllers are connected already (I think with RS485) and I can read/set the data from/to controllers (with “iTools OPC Server”), but I have to change my program so, that it works without “OPC Server”
@Putnam:
In the meantime I found out, why I got an error with  “my modbus serial query.vi” (the solution was very simple, I had to close the OPC-Server ). 
It runs now and I try to understand now how the VI exactly works. 
Maybe you can help me with it? 
I try to explain what I understood, if something is wrong, tell my please: 
The “my modbus serial query.vi” allows to read the multiple values (maximum 125 register) (default block read size is 125) from controller (I can see the data in the register array). In each register I have values for different variables. The Modbus address of Loop1 PV (I need this value) is known ( 00001, Eurotherm manual).
Does it mean that the first element in the register-array is the value for the temperature from Loop 1 ?! (multiplicated by a factor, if it is correct, how can I find out this factor? It is linear?)
And if I need the value of Loop2 (the address is 01025), I have to set the start address for example to 1000 and in this case the 25-th element in register-array is the value for PV Loop 2 ?! 
I got this idea, after I left the laboratory and could not try it out. I can do it first at Monday, but I would know if it is correct what I think.
If it is correct, I think I will able to change  “my modbus serial query.vi” on my own, that it works in my program.
Or there is a better example/solution than “my modbus serial query.vi” ?!
The other problem would be writing of temperature, but I will ask about it later . First temperature READING problem!!  
Thank you! 
Alexander.
Message Edited by alexphysiker on 01-29-2010 05:30 PM