??? September 2022 NAR Electronic Rocketeer newsletter

[Antares JS]

I think that Steve is being conservative... VERY conservative. Has anyone actually seen an ematch spontaneously firing? Shuffling your feet on the carpet and touching one lead to the doorknob doesn't count...

I got the hair on my arm singed off once by an errant BP charge while I was installing my electronics into the rocket. I'm pretty sure ESD was to blame, but mostly because I don't have a better explanation.

 

[Hobie1dog]

You’ll need to log in to get to https://www.nar.org/members/magazine-archives/sport-rocketry-magazine/

from the front page MemberResources->PublicationArchives->SportRocketryMagazine you can then choose an issue to browse online or to download a PDF.

I'm not a member, so that's not going to work.

 

[WillMarchant]

I'm not a member, so that's not going to work.

You'll be able to buy it from NARTS https://blastzone.org/nar/narts/store.asp?groupid=1111200711430450 sometime.

 

[Johnly]

I was one of the RSOs at the NASA SLP launch when a team's transmitter fired off one of their deployment charges. There was an incident review after the launch and I can confirm that the team switched their RF power for their payload from the ~200mW used during their prior test flights to full available RF power which was several watts. It was a commercial altimeter that fired, and not a self-made unit (which is still permitted for the NASA Student Launch Program).

10+ years ago I worked in an ISO 17025 EMC testing lab and ran the 1000-4-3 RF Immunity test protocol on flashbulbs and e-matches with leads only and attached to powered altimeters. I gradually increased the power level of the test protocol to the maximum available, which placed the pyro devices in a modulated RF field of over 100 volts/meter. There was no effect on the raw elements.
The next phase was where things happened. Testing of an Adept Alts2s 50k fired one of the channels that was connected to a flashbulb at an elevated power level. The postmortem indicated that the firing circuit of the altimeter was fried and the output FET was shorted, which then caused the flashbulb to fire.
The take away from this is that coupling the power from the RF field into the altimeter electronics is the more likely mode of accidental firing.

 

[Johnly]

There have been documented instances of some radios (IIRC the early Garmin Astro was notorious for doing this to some altimeters) triggering altimeters by inducing noise, which is not the same as firing the ematch directly.

The 2023 SL Handbook says only "The recovery system electronics will be shielded from all onboard transmitting devices to avoid
inadvertent excitation of the recovery system electronics." I don't see an explicit power restriction.

It's there:
2.23.8. Transmissions from onboard transmitters, which are active at any point prior to landing, will not
exceed 250 mW of power (per transmitter).

 

[cerving]

I was one of the RSOs at the NASA SLP launch when a team's transmitter fired off one of their deployment charges. There was an incident review after the launch and I can confirm that the team switched their RF power for their payload from the ~200mW used during their prior test flights to full available RF power which was several watts. It was a commercial altimeter that fired, and not a self-made unit (which is still permitted for the NASA Student Launch Program).

10+ years ago I worked in an ISO 17025 EMC testing lab and ran the 1000-4-3 RF Immunity test protocol on flashbulbs and e-matches with leads only and attached to powered altimeters. I gradually increased the power level of the test protocol to the maximum available, which placed the pyro devices in a modulated RF field of over 100 volts/meter. There was no effect on the raw elements.
The next phase was where things happened. Testing of an Adept Alts2s 50k fired one of the channels that was connected to a flashbulb at an elevated power level. The postmortem indicated that the firing circuit of the altimeter was fried and the output FET was shorted, which then caused the flashbulb to fire.
The take away from this is that coupling the power from the RF field into the altimeter electronics is the more likely mode of accidental firing.

That's great input, I like seeing actual test data. 100 V/m at one meter is a lot of RF power.

 

[Johnly]

I started flying when flashbulbs were still in common use and they are quirky devices. Unlike many believe, they are not low current devices like e-matches, as you can pass several hundred mA of current through them steady state and not have them fire, but the are like an avalanche diode and the smallest high current spike like that delivered from a capacitor will activate them. The IR they emanate when firing will also synergistic fire another flashbulb if it is withing ~1/2".

 

[cls]

The take away from this is that coupling the power from the RF field into the altimeter electronics is the more likely mode of accidental firing.

thanks for posting this

 

[rocket_troy]

I started flying when flashbulbs were still in common use and they are quirky devices. Unlike many believe, they are not low current devices like e-matches, as you can pass several hundred mA of current through them steady state and not have them fire, but the are like an avalanche diode and the smallest high current spike like that delivered from a capacitor will activate them. The IR they emanate when firing will also synergistic fire another flashbulb if it is withing ~1/2".

I've personally had one go off by just *touching* it and I'm not the only one. Another club member had one go off by picking it up in his hand. In both cases there were no leads or anything attached to the bulbs. I'm assuming it was electrostatic cause. The incidents certainly terminated my days of using them.

TP

 

[cls]

If I *wanted* to conduct a magic trick and place an Ematch on a table top and fire it without the wires connected to anything, sure I could do that, holding a 5W 2way UHF transceiver radio under the table in close proximity to the Ematch, but, the wires of the Ematch would need to be cut to the 1/4 wavelength of the carrier frequency of the transceiver and be in a dipole configuration (unpractical for general wiring in rocketry applications).

Ok, I did that today. A bunch of different ways.

Doesn't work. Not with 5w. Not with long wires, or tuned 1/4 wave wires.

Sorry, wrong.

 

[cls]

I guess to prove that the ematch is still live, I should post both resistance measurement and a video of setting it off.

But first, I'm intrigued. I have 100w on 432MHz and 20dBi antenna... 10kW ERP. That ought to set it off! But I bet it doesn't.

I bet I can set it off with a diode across the two wires. That would explain why folks have observed such failures with the ematch connected to the altimeter. The FET driver DS junction is a diode.

Static... How to test that... I was reminded of my electricity class in 4th grade, we had a Van Der Graff generator. Lots of fun with hair flying around etc.

Too lazy to build one right 5. Anyone?

 

[waltr]

At work we have an ESD gun for pre-testing electronics before having them go to CE certification (big $$).
This is what one would use to test e-match and ignite susceptibility to static.
Not sure what my co-workers would think of e-matches going off in the R&D lab.....

I've never witnessed any of these going off by static but have seen bad altimeter's set off deployment charges. No one got hurt but did get a big scare. For DD altimeters I do not power them on until on the pad.

I do practice safe handling... e-match and igniter leads shorted until they need to be connected.
Never install ignites in motors until ready to launch.
Maybe none of these will even go off unexpectedly but I prefer to take precautions.

 

[WillMarchant]

At work we have an ESD gun for pre-testing electronics before having them go to CE certification (big $$).
This is what one would use to test e-match and ignite susceptibility to static.
Not sure what my co-workers would think of e-matches going off in the R&D lab.....

was shown in our last ESD certification class.