Beckhoff and PLC

Hey guys.

I have been asked to interface a Beckhoff Cx9001-0001, to a DMX system, has anybody done this, or anything similar?

If you have could you let us know what you did and where to start?

And what is "DMX" ?
Post a link.

reece,

I assume by DMX ( http://en.wikipedia.org/wiki/DMX_512 ) you mean DMX-512, the theatrical lighting control standard, and not the rap artist ( http://en.wikipedia.org/wiki/DMX_(rapper) ).

Assuming this is correct, are you trying to control the PLC with DMX, or have it control other devices (lighting, hazers, foggers, etc.) via DMX?

If it has to control other devices, take a look at these:

http://home.att.net/~northlightsystems/dmx512encoder.htm

The PLC can output a 0-10v signal and these cards will encode that signal into a DMX value.

If you need the PLC to be controlled by a DMX value, look at these:

http://home.att.net/~northlightsystems/dmx512decoder.htm

The PLC will need 0-10v analog inputs to read the voltage generated by PLC.

Keep in mind that DMX is an 8-bit standard, so there are only 265 possible analog values; this is much less than the average PLC analog card with 12 or 16 bit resolution.

What is the specific application - are you trying to control lighting with a PLC? While possible, PLCs are not really suited to this; a light board would be a much better choice for acting as the controller / transmitter.

Also, I know of no PLC that can directly output a DMX signal. The physical format is RS-485, but the data format is nothing like a PLC is capable of generating.

I hope this helps. Please provide us with more info about your specific project.


-rpoet

Hi Reece, as you probably already know, Beckhoff is planning on releasing an EtherCAT DMX Master interface...
http://www.beckhoff.com/english.asp?EtherCAT/el6851.htm

As you can see from the bottom of that web page, the release is scheduled for the end of this year, however, that date may slip. After the release, there should be supporting documentation.

Beckhoff has already released the EL6851, though at the moment there is no supporting documentation.

Yes i do mean the DMX512 as appose to the rapper.

The details of the job are still abit scetchy though, im led to beleieve that they would like a touch screen to overided some of the DMX controls, for when the Stage is not in use for a preformace and they just want to create an atmosphere for a presentation and rather then having to know the DMX controls, any one can just go and press a button on the touch screen.

reece,
I stand corrected. I was not aware that Beckhoff had released a DMX module - very cool.

Also take a look at these devices from Johnson Systems:

http://www.johnsonsystems.com/cs_2800.htm

I don't know muck about the Beckhoff module, but you may need to consider how the touchpanel solution you're providing interfaces with the needs of theatrical productions. Typically, setups like this use a highest-takes-precedence. That is to say, that the highest value for a particular channel, whether it comes from the light board or your controller, is sent on to the dimmer rack to control the lights.

Controllers like the one you're designing will have a "worklights" setting for daily use, as well as a "stage" setting that allows the light board to take full control. There is typically a lockout feature so that worklights cannot be turned on accidentally during a show.

Also extremely helpful is the ability to record a snapshot of the current DMX values. Since the location of worklights can change form production to production depending on where free dimmers are located, it's VERY helpful to be able to set a "look" on the light baord and then record that look in the controller. That way, when someone walks into the space and hits the "worklights" button, only the worklights come on, and the stage lighting stays off, saving their expensive lamps and gels.

Many companies have come out with specific products to do just this, and most are terrible. Electronic Theatre Controls' (ETC) Unison system - possibly the least user-friendly and most buggy POS out there. My point is, make sure to ask the end user how they will be using it, and make sure it's easy and straightforward.

Post back here, or PM me if you have any other questions about this. I work in the entertainment industry, and have spec'ed these systems before.

Beckhoff's release of that module has me thinking... Most PLCs do RS-485 COMs already. All that's really needed is some firmware to make almost any PLC DMX control.... manufactures?? Are you listening??


-rpoet

Beckhoff DMX Sample Code

reece, I do not have documentation yet, either, however I was able to locate a sample program, see attached. (Disclaimer: I haven't tested this myself)

The full documentation, including a TwinCAT Library for DMX communications has been released, the online version is here...
http://infosys.beckhoff.com/content/1033/el6851/html/bt_el6851_intro.htm

DMX TwinCAT Library documentation here...
http://infosys.beckhoff.com/content/1033/el6851/html/fb_dmxoverview.htm