Rotork Pakscan

Hi Cameron,

I had a project several years ago with two Modicon Compact 984-145s connecting via Modbus Plus to a BM85 Bridge Mux, which in turn used Modbus RTU to connect to the same Pakscan master station with 15 IQ actuators. Between my PLC address spreadsheets and what I remember, here are some notes:

IIRC, the Pakscan Modbus port is DCE, not DTE like the PLC, so your cable is Tx->Tx, Rx

Thanks, Mike. That is quite a help. A couple of questions though:

The examples in the back of the Pakscan Modbus Spec (Doc S171E) shows FCU's in blocks of 60! I don't doubt you, I'm just a bit confused.. Is there a better document I should read?

This was a lot simpler two years ago when I had direct Modbus RS485 to Limitorque valve actuators. Anyway...

Blame a memory glitch after 5 years and not having the Pakscan manual. This time I downloaded the document and read it first. It is 4 blocks x

60 valves/block, not 30 valves.

That's a read/write area. I was reading the Position Control for all

15 valves, but only writing the last two. The other gates and valves were all controlled manually at the master station.

That is incorrect. Valves #1 thru #15 were FCU1 thru FCU15. The problem stems from the difference between Modicon addresses and Modbus message formatting. In a Modicon PLC, addresses start at 00001 (coils), 10001 (input bits), 30001 (input registers) and 40001 (holding registers). In a Modbus message, the starting address is defined by the _offset_ from the first address, i.e. holding register offset 7 = 40008. The register locations in the Pakscan are actually the offsets, so you have to add 1 to get the correct Modicon address. 0x, 1x, 3x and 4x are implied by the message type. See Note 3 on page 32 of S171E.

I don't follow you. Is this the Modbus or Pakscan address?

Mike

No arguments from me there. If the IQ-series wasn't cheaper and easier all 'round, the customer would be getting Limitorque for this job too! :-)

Thanks, Mike. I'm getting the picture.

Gotcha.

'kay.. I think. I must be getting old - that addressing structure will take a while to get my head around.

Pakscan address. Caused by my misunderstanding of the above. As you've pointed out: Valve #1 = FCU1 = Pakscan address 01. It's the offset business that is stuffing me up.

Thanks again, Mike.

Cameron:-)

Hi Cameron,

We implemented one of these several years ago, along with a parallel network of the major competitor. Both RS485 IIRC. One of the networks suffered bigtime during an electrical storm, heaps of blown inputs. I really can't recall which of the two it was, and even if I could I'd probably take the

5th.... Cheers

Thanks for the advice, Bruce - it's a valid point. I will make sure we put surge protection (RS485) on the bus.

What exactly are you referring to by "take the 5th"? Is Pakscan *that* much of a pain to implement?

Cameron:-)