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Trouble reading from Watlow 96 Controller using Modbus 232

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I am using the Watlow Series 96 controller and trying to communicate with it using Labview. The controller is configured to communicate over RS232 at 9600 baud.  I've connected to the communications port using a null-modem cable from the DB9 Serial port on the PXIe-8133. 

I've tried using the watlow library but it doesn't seem to do anything. The VI doesn't error out but it also doesn't return anything when I read or write regardless of which register I try.  I've checked that Com1 is configured to the correct baud rate in NI-MAX but even the Visa test panel is unable to read from the controller. 


Please let me know if anyone has any suggestions. 

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Message 1 of 4

I have never used this product, and just some basic things came to my mind, sorry if you checked these already:

  • Do you have some software to test from the producer? Does it work with the same cabling?
  • Are you sure your product model version support RS232? Maybe it requires RS485?
  • I had a quick look at the manual if this is your product (, did you check the cabling is properly done (Figure 3.7b)?
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Message 2 of 4

1. I called Watlow and the existing library that I attached is for a different controller series. The 96 is old enough that they don't have anything available for it, they say that Labview Modbus library should work but I've yet to succeed.

2. According to the Setup menu on the controller, I have the RS232 version.

3. I've checked that the cabling is correct going from PXI to communications port. I guess I haven't checked that the wiring inside the oven that actually connects the communications port to the controller is correct so maybe I'll try that. 

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Message 3 of 4
Accepted by valcham

After more investigation it seems like the error lies with the controller itself and since we're getting a different one in a few days I'm going to lay this to rest. 

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Message 4 of 4