Is This Right?

[masterelectrician2112]

I was watching a behind the scenes of a concert DVD set today, and in the video, there was a section on pyro. He talked through how he sets up propane heads, and he talked about connecting the main propane line, the pilot light light, etc. Then, the last thing he connected was, as he said, a dmx line to control the propane heads. From everything I have read on this site, it is bad to control pyro with dmx. Is this pyrotechnician wrong using dmx?

 

[Footer]

It depends on the implementation. If there was a dead man involved, yes its fine. If it was controlled completely via dmx then that is a bit of an issue. Also it is possible that he just called it dmx because it was a 5 pin cable and might not be actually using the dmx protocol. Which show are you talking about?

sent from my HTC Incredible

 

[masterelectrician2112]

Oh ok. It was the Rush Snakes and Arrows tour. Pyrotek was the company.

 

[MNBallet]

It is not wrong to use a DMX controller for controling a pyro system. What is wrong is using the same board that also controls your lighting. Using the same board that is attached to your lighting system is a bad idea because you can be doing a dimmer check and set something off. The Gruesome Twosome tour with Rob Zombie and Alice Cooper uses two DMX controllers, one to control the height of each individual propane head by a fader and the other to ignite by a bump button. The deadman switch or a E-stop is not in the DMX signal path.
Remember that they are only using the DMX board for a control interface, a physical button or fader to control something else. These systems are custom designed and not something that you could just buy from a DJ type store. The important part of the system is what takes that DMX signal and turns it into a command to open a propane valve.

Kenneth Pogin
licenced Pyro

 

[Les]

It is not wrong to use a DMX controller for controling a pyro system. What is wrong is using the same board that also controls your lighting. Using the same board that is attached to your lighting system is a bad idea because you can be doing a dimmer check and set something off

I thought it was because the DMX protocol has no error check (it just spits out commands)?

I guess the deadman switch is the magic link.

 

[Footer]

It is not wrong to use a DMX controller for controling a pyro system. What is wrong is using the same board that also controls your lighting. Using the same board that is attached to your lighting system is a bad idea because you can be doing a dimmer check and set something off. The Gruesome Twosome tour with Rob Zombie and Alice Cooper uses two DMX controllers, one to control the height of each individual propane head by a fader and the other to ignite by a bump button. The deadman switch or a E-stop is not in the DMX signal path.

I don't care if people are doing it or not, but you should not be using DMX to control anything that has the ability to harm someone. I have seen DMX systems that have been working flawlessly for months or years but get erratic because of the stupidest thing, be it a cable that got out of whack or a dirty connection. Ever seen a moving light freak out after working fine for days on end? Do you really want that to happen with a flame cannon? DMX receivers have no way of confirming a command came from the console. The protocol is simply not safe to use for pyro/rigging/automation. It can be used to cue the control systems that controls the final effect but there has to be some type of middle man with a safety system in place. Not having an deadman in place and directly controlling anything with DMX that is life threatening is simply irresponsible. The protocol was speced to control lighting and was never intended to control anything else. There are plenty of other process control languages that can safely be used with these systems. Leave DMX to control the lights.

Just because someone wired up a valve to a DMX interface does not mean you should do it or that it is safe.

 

[ajb]

It is not wrong to use a DMX controller for controling a pyro system. What is wrong is using the same board that also controls your lighting.

What is REALLY wrong is using a protocol with zero provision for error detection as the sole means of control for a system a malfunction of which could result in serious injury or death. It doesn't matter one bit what else is or is not controlled by the system, DMX is not suitable for controlling pyro, flying effects, automated scenery, or anything else that could seriously hurt someone. NFPA 79 addresses this:

9.2.7.4 Serial Data Communication. In a machine where the control of safety critical functions relies on serial data transfer, correct communcations shall be ensured by using an error detection method that is able to cope with up to three error bits in any command sequence.

A way around this is to ensure that your system does not 'rely' on the serial communication (DMX) by incorporating additional controls in the system that receives the DMX signal. IE, a deadman switch, which is incidentally also covered by NFPA 79, though it uses the less colorful term "Enabling Control":

9.2.5.7.1 An enabling control function incorporating the use of an enabling device shall, when activated, allow machine operation to be initiated by a separate start control and, when deactivated, stop the machine and prevent initiation of machine operation.

In this case, the DMX signal transports the "separate start control".

EDIT: I suppose that's what I get for taking the time to cite authority, beaten twice!

 

[MNBallet]

What is REALLY wrong is using a protocol with zero provision for error detection as the sole means of control for a system a malfunction of which could result in serious injury or death. It doesn't matter one bit what else is or is not controlled by the system, DMX is not suitable for controlling pyro, flying effects, automated scenery, or anything else that could seriously hurt someone.



A way around this is to ensure that your system does not 'rely' on the serial communication (DMX) by incorporating additional controls in the system that receives the DMX signal. IE, a deadman switch, which is incidentally also covered by NFPA 79, though it uses the less colorful term "Enabling Control":



In this case, the DMX signal transports the "separate start control".

Correct. I was not going to get into more detail about what the DMX boards are connecting to. But if you feel that there are better control languages out there, why are professional pyro companies like Pyrotek using it to interface into the system?

 

[Footer]

Correct. I was not going to get into more detail about what the DMX boards are connecting to. But if you feel that there are better control languages out there, why are professional pyro companies like Pyrotek using it to interface into the system?

Just in our industry acn, artnet, shownet, and ma net all offer error checking. The TCP protocol that is the basis for all computer networking and has been around longer then dmx offers error checking. Honeywell and mitsubishi both have protocols that are designed to operate in these situations.

They use dmx because that's what they know. They should not be using dmx to directly control any of their gear. Dmx is an extremly easy protocol to use. Everyone understands it enough to get a show up. OEM boards are cheap. The cable is everywhere. Control surfaces are available and everyone knows how they work. Just because you can do it not mean you should.


sent from my HTC Incredible

 

[len]

It's quite possible they are using dmx, but with dead man switches and all the other necessary safety precautions. You just didn't see it because it would have slowed the narrative of the show down. Documentaries should be informative, but they shouldn't be "how-to" videos.

 

[masterelectrician2112]

So then the final conclusion is that dmx is safe to use with pyro as long as deadman switches, etc. are in place, or am I missing something?

 

[Footer]

So then the final conclusion is that dmx is safe to use with pyro as long as deadman switches, etc. are in place, or am I missing something?

Essentially, yes. The dmx can not control the effect without another signal present from a deadman, proximity switch, etc.


sent from my HTC Incredible

 

[MNBallet]

So then the final conclusion is that dmx is safe to use with pyro as long as deadman switches, etc. are in place, or am I missing something?

Think of the DMX boards the R&R tours are using as your thermostat that controls your home furnace. The thermostat doesn't actually heat your house it just controls the unit that does the heating. All the safety stuff in in the unit that controls the flames, for example:They have electronic eyes that "see" if the pilot light is lit and will not open a valve if it doesn't. I too was under the impression that DMX boards were a total taboo until I starting working some larger R&R shows. I asked the touring Pyro guys about it and they gently chuckled. I miss the days of setting off pre-packaged pryo like gerbs and airbursts. Hazmat shipping cost for these type of materials has just skyrocketed and now most tours just use propane because it can be got locally and very cheap.

 

[themuzicman]

One of the production companies I do some work for uses DMX for pyro. My first day on the job I asked the pyrotech about it, because I had always assumed it was a no-no.

His response was that in pyro, the physical dmx cable is reversed (Female is input / Male is output) so as not to accidentally connect lighting to pyro! You use a second board on a completely separate dmx run. That was all I remembered, but they had been doing it for years and are a fairly reputable company in my region!

 

[ajb]

One of the production companies I do some work for uses DMX for pyro. My first day on the job I asked the pyrotech about it, because I had always assumed it was a no-no.

His response was that in pyro, the physical dmx cable is reversed (Female is input / Male is output) so as not to accidentally connect lighting to pyro! You use a second board on a completely separate dmx run.

Neither of these practices does a good god****ed thing to address the underlying issue with DMX: The absolute lack of any form of error detection. It doesn't matter how good your other practices are, if you have DMX carrying sole control for safety critical functions, you're risking people's lives. End of story.

If they had said that the DMX signal only carries the timing and level, and there's someone with a clear view of the pyro with his hand on a deadman switch that enables the pyro device to react to those timing and level controls, then fine, that's a good way to do it.

That was all I remembered, but they had been doing it for years and are a fairly reputable company in my region!

Just goes to show you that reputation sometimes doesn't mean a **** thing.