How to use LabView to Fire Pyros (electro-explosive devices)

[ichthyicide]

I've been searching NI Forums and google about this subject but can't find much of anything. 

Can someone help me figure out what modules I need to fire a few different pyros (aka electro-explosive devices, squibs) such as cable cutters, bottle openers, etc?  We use a 9172 chassis.  I can monitor and record data from a pressure transducer with a 9205 module and output voltage with a 9263 module without any trouble.  I just can't output sufficient current with the equipment I have now.  The pyros I have to use require anywhere from 1 to 5 amps and so far up to 6.15 volts to activate.

I haven't seen any module that can output that much current.  However, the 9481 relay module might be promising if it can give me another amp or two at lower voltage.  The range says 4 amps at 30 vDC.  My eventual plan is to have the VI fire the first pyro when the pressure reaches a specified point and then fire the second pyro at a specified time after the first.

Someone out there has to have done something like this before.

I'll worry about the programming after I figure out the hardware.

Thanks to anyone who can help

[thoult]

You usually have two options: run a SSR / EMR device, which will often limit you to a small number count; or, preferably, use a nice simple DIO device that can only supply small currents, but enough to switch relays / optoswitches and some interface electronics of your own to do the heavy work.

For instance, and at a much smaller current rating, I need to power my device under test (DUT) with 5 V, 100 mA. I have a power enable output from my DAQ system, which is a 5 V TTL line that sets the enable/disable pin on a voltage regulator. It's this regulator that supplies the voltage and current I need. The downside of this is needing to make my own electronics to interface with my DAQ system... although that's really not a problem for me or my employer!

There are C series SSR and EMR devices, but as you say, they don't appear to be able to match what you're after, current wise. I suspect you'll be forced to go down the second route.

[Sam_Sharp]

The NI 9477 digital output module has 32 channels and can drive up to 1A per channel (0.625A continuous, up to 20A per module). If you need more than 1A then you can parallel up multiple channels and write to them all directly (i.e. write to the port 0:7 rather than DO0, DO1 etc.) to make sure you don't overload a single channel.

Either that, or like others have said - use a digital output module connected to an appropriate relay/high-current transistor circuit for firing the pyros.

[ejkaiser · Accepted solution]

I wouldn't recommend to use parallel digital outputs. They may not really switch exactly synchronously. So during swiching on and off you may overload and destroy the channels switching first and last respectively.

I would recommend to add a simple electromechanical or solid state relay.

[crossrulz]

I'm in the camp of using a simple DIO module and use a Solid State Relay (SSR) to switch on your high power supply.

[Sam_Sharp]

It's actually mentioned as something you can do in the module documentation - with the same caveat that I gave that you should write to ports rather than individual DO items (I know that when using FPGA nodes it writes to I/O nodes sequentially rather than simultaneously).

http://www.ni.com/pdf/manuals/374182c.pdf

[LV_Pro]

And whatever route you go, put some safety interlock's on the det lines, with a key switch, so that you can absolutely, positively, remove any possibility of triggering accidently while you or some other tech are connecting the devices. I know it goes with out saying, but when you add complexity to a system like this ...

Also, pay a lot of attention to the state that the control circuit comes up from off in, some will output a high or low on all channels until they are up and running.

It is definitely a good idea to have a layer between your I/O card and its "target", like the SSR + external power supply, mentioned before. Source the power supply to be able to supply all of the currents needed (i.e. if setting off 5 squibs that each need 3A, then you'll need a supply that can source 15A +, which precludes a Digital I/O card)

[RTSLVU]

LV_Pro has some good points you do not want somthing like what happend in San Fransisco to happen to you.

https://www.youtube.com/watch?v=nCcmmRkVveA

 Due to a compuer glitch the entire firworks show fired all at once.

[ichthyicide]

ejkaiser:

Thanks for the input.  This solution is nearly unanimous.  I've asked our electronics consultant to help me find a relay that meets our needs.  I am a LabView and electronics novice.  I am trying to use my basic LabView training to accomplish this task instead of the old standby of firing the pyro by plugging it directly into the power supply.  I'll let everyone know how it goes after we run the test--hopefully this time next week.

[ichthyicide]

Sam_Sharp:

I'll keep this idea in mind when I have more time and resources.  My skill level is novice and I don't have a lot of time to figure this out.  Fortunately my employer is actively developing my training when time permits.

Thanks