Eurotherm bisynch

[bjlv]

Hello all:
I have a customer who was running just fine on old Eurotherm 815 controllers using the LabVIEW driver from Gary Johnson (originally for the 808 controller).  The 815s are starting to die, so they are swapping in new 2404 controllers.  I have worked successfully with those (and 2408) controllers in the Modbus style, but I never tried before in the bisynch mode that duplicates the communications of the 800 series controllers.  The 2404 is behaving a bit weirdly.  It listens just fine when I send a set point, but often won't answer well when I ask it for a current Process Value.  It answers just fine always when I ask for status.  The weird thing is that if it ever does start respondng to the PV request, it will respond correctly ever after until the 2404 is turned off.  The bad response is being seen by a customer about 1200 miles away, so I don't really know what the response is from the controller, but from the error message I know that the response is too short to be correct, but not zero length.  A correct response would be somethng like (\codes ON) "\02PV123.\03", but the response I am getting must be between 0 and 4 characters long to cause the error message.  Does anybody have any idea why this controller does this?
Bart

[Bush-Man]

Hi,

I suggest you to replace the communication unit of the Eurotherm with one with Modbus. It cost not so much, and from the Eurothem company, I have been told that the Bisynch protocol is dyeing and to prefer the ModBus protocol unit.

I had the same problems and it will be worst (I think...). If you want your application will work more years, then I suggest you to change the protocol.

Bush-Man

[mikeporter]

To really troubleshoot this you would need to know exactly what the controller is returning, but I agree with BushMan. Now is the time to bring things up to date. In fact you can use this problem as a justification for the upgrade.

It's been many years since I have looked at Gary's drivers, but as I recall they were written very well and it would be easy to make the lowest level routines "switchable" between bisync and modbus--in fact I'm thinkiing that at one point they were...

Actually, the beautiful thing is that the only real added cost to the customer is the code modifications because they are buying new controllers anyway!

Mike...

[bjlv]

Hi all:
I have read the suggestion about switching the 2404 to use Modbus, and I don't disagree with your reasoning, but it isn't really practical.  I actually did do another system for them hthat is all 2408s, and that one is Modnus.  The reason that the change won't work now is the customer now has a mix of 815s and 2404s.  The system has 6 controllers in it (on one serial port speaking RS-485), and the program handles them in a loop running through the six addresses.  There is no good way to know which controller ID goes with which type of controller.  We know we have the 2404s wired in correctly, as they do receive the setpoints just fine, and eventually for reasons I don't understand, the 2404 starts to behave just as the 815s do, until the 2404s are powered down for a while.  Then we are stuck for awhile again, and then good again.  I can easily rewrite the Read VI to stop complaining about the "bad command response", but I don't really like redefining what an error is just to make it go away.  If I had the system a bit closer, I would probably know what was really going on, but I just get phone calls and emails from the customer between production runs that last about 61 hours.   There is then a window of about 6 to 8 hours before the next run is started.  A bit tough to debug with that kind of access to the hardware.
Still hoping for the words of widom as to what the 2404 controller is up to.
Bart

[Conseils]

You might want to try using the Eurotherm iTools software and consider OPC.

One suggestion is that you could have an earth loop problem. With Bi-Sync you have to be really carefull that someone didn't connect to an earth point or leave something floating when it shouldn't. You can get all sorts of odd things happening under these conditions. Typically unreliable comms is one I have had.

[Brian_Beal]

I have never used BiSynch, but have much experience with Modbus.  I have never experienced any problems.  The iTools software only works with the Modbus protocol.  I am convinced that OPC is the way to go with Eurotherm and Labview.  All configuration and programming can be done through iTools, which it is very good at.  DAQ and other functions can be used with Labview through the Eurotherm Modbus server.