attempting to read registers on Watlow F4 temperature chamber controller via modbus_rtu instance

[Motorola_Bob]

All,

I am trying to read registers on a Watlow F4 temperature chamber
controller via the instance modbus_rtu instance, so using RS-232. I
can write to register 300 although it looks like the modbus-tk module
throws errors but I just catch the exception and move on. However,
when I attempt to read a register using the command:

self.RTU_handle.execute(1,cst.READ_HOLDING_REGISTERS,register,3) where
register is 100, I get an error that not response was received.

I can get the register value when I use proprietary Labview VIs from
test equity, maker of the temp controller.

Do you have any idea what may be wrong?

Thanks,

Bob

[Luc JEAN]

Hello Bob,
Just an idea, have you tried to read some other registers?
Is the Labview query the same?
Best
luc

2010/11/6 Motorola_Bob <bobwa...@gmail.com>

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[Motorola_Bob]

Luc,

I got it to work on Saturday (U.S. central time zone). It was the
number of expected bytes coming back was the issue I think, although I
don't have the code right in front of me.

You can add the Watlow F4 with RS-232 serial interface as another
supported device.

Bob

On Nov 6, 3:14 pm, Luc JEAN <luc.j...@gmail.com> wrote:
> Hello Bob,
> Just an idea, have you tried to read some other registers?
> Is the Labview query the same?
> Best
> luc
>

> 2010/11/6 Motorola_Bob <bobwalk...@gmail.com>

[Luc JEAN]

Hello Bob,
Congratulations and Thanks for the feedback.
I'll add this one to the list of tested device (Every modbus device should be supported ;-) )
Best
luc

2010/11/7 Motorola_Bob <bobwa...@gmail.com>

--
http://www.apidev.fr

[trinadh k]

Hi,

I have installed modbus-tk tools to control Watlow F4 temperature controller. I am using a RS232 to USB cable to connect between Watlow F4 chamber and Linux x86 host.

I am seeing the below error, can you please explain how to fix this

2020-09-08 07:26:46,988 INFO    modbus_rtu.__init__     MainThread      RtuMaster /dev/ttyUSB0 is opened

2020-09-08 07:26:46,988 INFO    run.main        MainThread      connected

2020-09-08 07:26:48,989 DEBUG   modbus.execute  MainThread      -> 1-3-0-100-0-3-68-20

2020-09-08 07:26:49,490 DEBUG   modbus.execute  MainThread      <-

Traceback (most recent call last):

  File "run.py", line 52, in <module>

    main()

  File "run.py", line 34, in main

    output = logger.info(master.execute(1, cst.READ_HOLDING_REGISTERS, 100, 3))

  File "/home/ssdlab/.local/lib/python2.7/site-packages/modbus_tk/utils.py", line 39, in new

    raise excpt

modbus_tk.exceptions.ModbusInvalidResponseError: Response length is invalid 0

Thanks,

Trinadh

[Luc JEAN]

Hello

It seems that your slave doesn’t answer to the request. You may have to check communication settings and cable.

I hope it helps

Best

luc

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[Knucklehead]

Your Watlow F4 does not have an RS232 interface. It is RS485. You need a different adpater:

https://www.watlow.com/-/media/documents/specification-sheets/win-ca-0518.ashx

[trinadh k]

Thanks for the responses,

I am having a thermal chamber from Espec which uses watlow F4 temperature controller. The communication interface is a RS232 port, hence i am using RS232 to USB cable for communication between the chamber and host. I did match the controller settings like address/Baudrate in the software/python code, will double check

Thanks,

Trinadh  

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