Red Lion to Watlow Comms

Rube

Member
Join Date
Sep 2003
Location
Fort Worth, Texas
Posts
958
Has anyone had any experience with a Watlow to Red Lion modbus comms setup? We have a pair of Watlow controllers that I want to set up to comm with a RL CSMSTRSX using modbus TCP/IP. The Watlow units are doing their thing, controlling a furnace, but I want to monitor them. I will not make any writes to the Watlow.

I have set the RL 2nd protocol for "Modbus TCP/IP Master" and I can see (display on the PC screen) that hex data and 16 bit data gets to the RL but I can't see the real data (temperature) in decimal form. I have tried using the Word, Long and Real settings on the tag mapping with no success.

I have used CAS's Modbus Scanner to read the Watlow data so I know I'm getting all the data from the Watlow to my ethernet. CAS does an "Auto Update" poll and the data stream follows the readings shown on the front of the Watlow so, again, I know I'm live to the ethernet. I also know that the RL is getting the hex and 16 bit data since it too shows what the Watlow shows.

I really just need to show the temperature in decimal form, that is being sent by the Watlow to the RL, on the PC screen. I'm sure I am just missing that "one little thing"! Any help would obviously be appreciated.
 
I haven't done any comms with Watlow devices before, but floats over Modbus can be a challenge. They usually use two registers (32 bits), and it depends on the format. I would select word as Real under the Source section in Crimson, then play with Manipulation and try Reverse Bytes and Reverse Words to see if the situation improves.

Do you know what format the Watlow uses to transmit Float data?

I found this link somewhat helpful:

http://www.chipkin.com/articles/how...32-bit-data-is-encoded-in-modbus-rtu-messages
 
Thanks Robert, I'll look into that though it would appear that the data is coming through in one register (example below). In the screen shots attached, I'm reading the data from the Watlow (line 362 on the CAS file). and all I've been able to display on the RL is shown on the RL file (attached).

CAS.jpg RL.jpg
 
Take a closer look at CAS.jpg - it says float32. Notice in the table the floats are only listed every other row... that tells me 32 bits are used. As you probably know, all registers (well, 3/4 types, not the bits) are 16bit so there is no restriction on how they are accessed - it just depends on how we look at what is in there.

Also check out this page... I found that 0x4292003D gives me 73.0 in 32 bit float. This isn't exact, but it is close for registers 362 and 363.

Try the other direction... 0x4292530a which is 73.162186 which is exact (to precision shown in picture). So your float is32 bits, register 361 and 362. Of course there are endianess issues and such, but playing with Word as Real and then the byte and word swaps, and selecting different starting registers should get you there in short order.
 
Thanks again for your help Robert. I had used the wrong type of tag--now that I have the right type, I'm seeing what I wanted too.

Thanks for the time, however. I'm not very versed in modbus and was thinking that was my issue.
 

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