Watlow Contollers - Any VIs?

[max]

Hello,

I need to write VIs to control the current model Watlow F4 controller
along with the obsolete Watlow 1500 controller. These are environmental
chamber controllers.

I have started on a crude Watlow 1500 VI. I can read the process variables
and the setpoints. I need to be able to also write to the controller. I
believe this one is simple enough.

The new one (F4) uses the Modbus protocol. That is where I am stuck. I
have unfortunately used up my budget ad can not get Busview or OPC server
software. At the moment, I just need to be able to monitor the process
variables. I have downloaded a generic VI for Modbus from a site in the
Netherlands (I can't remember its name, it at work where I don't have Newgroup
access)

Has anyone
worked with these two controllers?

Thanks
Max

[Brian_Vibert]

Modbus isn't too hard once you get the hang of it. Make sure you know if it uses ASCII mode or RTU mode Modbus (probably RTU if its anything like the watlow 96). If the vis you downloaded was from AIR Technical Automation then that should be a good starting point. I haven't used those vis only because I developed my own set before I found them, but they look good. It will help if you have the Modbus protocol manual so that you know what functions to use and what the command should be formated like for those functions. The manual can be found on the modicon website here: http://www.modicon.com/techpubs/TechPubNew/PI_MBUS_300.pdf . I have used my Modbus vis , which use similar methods to the AIR vis, to communicate with a Watlow 96 with much success. If
you need more detailed help let us know

Good luck!

Brian

[max]

In article <5065000000050000002A530000-1007855737000@exchange.ni.com>, Brian Vibert wrote:
>Modbus isn't too hard once you get the hang of it. Make sure you know
>if it uses ASCII mode or RTU mode Modbus (probably RTU if its anything
>like the watlow 96). If the vis you downloaded was from AIR Technical
>Automation then that should be a good starting point. I haven't used
>those vis only because I developed my own set before I found them, but
>they look good. It will help if you have the Modbus protocol manual
>so that you know what functions to use and what the command should be
>formated like for those functions. The manual can be found on the
>modicon website here:
>http://www.modicon.com/techpubs/TechPubNew/PI_MBUS_300.pdf . I have
>used m
y Modbus vis , which use similar methods to the AIR vis, to
>communicate with a Watlow 96 with much success. If you need more
>detailed help let us know
>
>Good luck!
>
>Brian


Brian,

I believe it was from AIR Technical. After a couple of false starts, I am
actually talking to the controller. It is a RTU mode. The AIR Technical VIs
help on that point calculating the CRC. Right now, I have to figure out
exactly how it is reporting negative temperature (I believe 2s Complement
which I have not had to deal with since grad school....).

I will check out the PDF.

Hopefully I will be able to do what I need to do. Its mainly get the process
variables and right them to a file. Late I need to write the setpoints back
to the controller. The big thing now is just monitoring.

Thanks
Max

[Brian_Vibert]

Now that you established communication the rest should be easy. I think the Watlow 96 uses 2s compliment for negative numbers, so it would make sense that your's does as well.

Good luck

Brian

[max]

Brian,

I believe it does. Thanks for the pointers. I have ran into one
minor problem. I believe I am sending commands to it too
quickly. I shall have to look into it some more. The VIs
from AIR made all the difference.

Thank
Max

In article <506500000005000000B7530000-1007855737000@exchange.ni.com>, Brian
Vibert wrote:
>Now that you established communication the rest should be easy. I
>think the Watlow 96 uses 2s compliment for negative numbers, so it
>would make sense that your's does as well.
>
>Good luck
>
>Brian

[Brian_Vibert]

Max,

I can't say that I've had that problem. What baud rate are you using? Make sure that you have sufficient time inbetween your messages. I think that slave must see at least 3.5 character times between messages or it will think it is all one big message. See the Message Framing section of the Modbus manual for details.

Good luck

Brian

[max]

In article <506500000005000000EE530000-1007855737000@exchange.ni.com>,
x@no.email says...
>
>Max,
>
>I can't say that I've had that problem. What baud rate are you using?
>Make sure that you have sufficient time inbetween your messages. I
>think that slave must see at least 3.5 character times between
>messages or it will think it is all one big message. See the Message
>Framing section of the Modbus manual for details.
>

Brian,

I do believe that is the problem. I am using 9600. Before I read
your message, I put in a 200ms wait state. Now I will shorten it.
It should speed up the program.

Thanks
Max

>Good luck
>
>Brian

[jmpugh]

Could anyone kindly point me in the direction of these AIR Technical Automation VIs? I've got two F4DH's coming in and since I've never used Modbus before I'm trying to find every angle I can to ease the process. I'll be monitoring them as well as plotting a relative hummidity and temperature versus time graph. Thanks guys!

-- Jason

[BarryGRAEllc]

The Watlow F4 does use modbus, but can also use rs-232, see the manual. I have written VI's this way. In fact it is right in front of me. Set comm on F4 for rs232 unit #1.

FYI, if you set the resolution to 20.1 (1 decimal place) you will have to rescale all your writes and readbacks for setpoints and temp in LV cause the F4 doesn't change the data format.

[jmpugh]

Thanks for the tip! Between the baud rate settings and data formats, hopefully there won't be too many surprises. While I would be more comfortable working with RS-232 (mainly because I've done it before) the fact that we are going to be controlling two of them might leave RS-485 to be the better method. That and the "newer" method is more impressive. 😉

-- Jason