Help With Processing Serial Communications.. Please

[kieranmonk]

Hi 

 

I am trying to import data into DAQ factory via a rs485 connection from a VIPA CPU 214 ser.

 

The original system had a number of analog inputs, which were converted to serial communications with the VIPA unit at one end. These were sent via fiber optic over some distance and then another VIPA unit converted the serial back to analog outputs which we then imported in to DAQ factory with a labjack.

 

However one of the Vipa units is damaged and we can't get another.

 

So my thought was to simply import the serial data directly into daqfactory, thus removing the need for the serial to analog conversion by the receiving VIPA unit and the subsequent, conversion from analog back to digital by the labjack unit. 

 

I have made the  connection in daqfactory and the comms monitor is receiving the following data stream

 

Tx: \002\003\000\001\000\001\213\249

Rx: \254\158\234\254\254\254\254\158\254\254\254\254\254\254\118\022\114\060\246\014\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254\254

 

as there 79 channels on the system, and I am receiving 78, 3 digit signals separated by backslashes after the Rx: tag, i am assuming this is the correct serial feed.

 

My task now is to extract these 3 digit packets into separate channels in daqfactory. (well actually they should be pairs with the signal plus and minus voltages so there should be 39 signal pairs)

 

I have read around a lot but still have no idea how I might achieve this (I have very little knowledge on serial communications but I am fairly faimiler with daqfactory)

 

Any help would be greatly received 

 

Thanks

 

Kieran

 

 

 

[AzeoTech]

What exactly is the protocol?  How are the values packed into that response?

[SteveMyres]

It seems unlikely that each byte is a value, because then they'd be 8-bit resolution, which is pretty low for PLC inputs.  I bet there's some sort of (standard or custom-engineered) protocol involved.  Try injecting some known data by manipulating the various analog inputs on the other end and see what it does to the byte values.  Plus, 78 bytes obviously cannot transmit 79 values, even at one byte resolution.  I bet it's just a coincidence.

 

Also, most VIPA stuff is software and hardware compatible with Siemens S7 stuff.  Have you looked into replacing the broken unit with a currently available Siemens alternative?

 

Also, don't forget that you have the option to replace both ends.  Doing something like this isn't unheard of (analog-serial-replicated analog).  However, if the data is going nowhere but into DAQ Factory, I agree that it's way cleaner to look at the serial data than convert it back into analog, and then BACK into digital with a LabJack.

 

But then that brings us to yet another option.  You could, whether with this PLC, or with another (or other SCADA product) get the data on the wire to be something industry-standard like Modbus (RTU or TCP) or Allen-Bradley DF1 that is already supported in DAQ Factory and you won't have to worry about trying to decipher the protocol.