Constant continuity checking

Constant continuity checking

Post by Wayne Johnso » Thu, 23 Feb 2006 03:19:03



I'm designing a new high tech launch controller.  I have one question
concerning continuity checking.

I plan to use a very low current continuity check, on the order of 1
microamp (.0000001 amps).  This should be low enough to safely test
just about any igniter, including flash bulbs.

Would it be acceptably safe to leave that current flow at all times?
That way you don't need to push a button to test continuity?  It would
also make it easier to see marginal connections, just keep at it till
the light stays green...

 
 
 

Constant continuity checking

Post by Cranny Dan » Thu, 23 Feb 2006 04:14:17



Quote:
> I'm designing a new high tech launch controller.  I have one question
> concerning continuity checking.

Hi Wayne,

more and more I see launch controllers being build with NO continuity
checking.

the club I belong to does not have any continuity checks and launches go
just as fine if not better then launches I attend with continuity checked.

I built mine this way also and it serve me well, and I never need fear a
continuity check ignition.

I mean why run current into an igniter if you don't plan to set it off ?

Really, if the igniter you chose had continuity when you checked it outside
the motor,
why check it inside the motor and run any risk ?

Also, I really would not want to have current running into my igniters or
matches at a launch continuously.

Just some food for thought.

CD

Quote:
> I plan to use a very low current continuity check, on the order of 1
> microamp (.0000001 amps).  This should be low enough to safely test
> just about any igniter, including flash bulbs.

> Would it be acceptably safe to leave that current flow at all times?
> That way you don't need to push a button to test continuity?  It would
> also make it easier to see marginal connections, just keep at it till
> the light stays green...


 
 
 

Constant continuity checking

Post by Wayne Johnso » Thu, 23 Feb 2006 05:35:39


We have quite a few High Power flights, using copperheads.  Continuity
serves us well there.
 
 
 

Constant continuity checking

Post by Cranny Dan » Thu, 23 Feb 2006 05:54:35



Quote:
> We have quite a few High Power flights, using copperheads.  Continuity
> serves us well there.

Hi Wayne,

Hi power flight is where having no continuity checks the best.

Most hi powered flight is done with either Hi-current igniters like
quick-burst ,
or with ematches like Oxral. Both are better to check before they are put in
the motor.

Copperheads and Hi-power are contradictory right ?

AT hi power motors come with first fires, Pro38/54 come with E-match, Loki
and AMW have you use your own, we use quick-burst.

Aero-Tech mid power still comes with Copperheads, and those are best split
with a match or many of the other tricks.

I still don't want to run current into something while I'm at the pad.

CD

 
 
 

Constant continuity checking

Post by J.A. Miche » Thu, 23 Feb 2006 07:26:30


Old skool Aerotech HPR loads came with copperheads.  They sucked just as bad
for HPR then as they do for mid-power now.

--
Joe Michel
NAR 82797 L2
http://geocities.com/jm44316


Quote:


>> We have quite a few High Power flights, using copperheads.  Continuity
>> serves us well there.

> Hi Wayne,

> Hi power flight is where having no continuity checks the best.

> Most hi powered flight is done with either Hi-current igniters like
> quick-burst ,
> or with ematches like Oxral. Both are better to check before they are put
> in the motor.

> Copperheads and Hi-power are contradictory right ?

> AT hi power motors come with first fires, Pro38/54 come with E-match, Loki
> and AMW have you use your own, we use quick-burst.

> Aero-Tech mid power still comes with Copperheads, and those are best split
> with a match or many of the other tricks.

> I still don't want to run current into something while I'm at the pad.

> CD

 
 
 

Constant continuity checking

Post by Bob Kapl » Thu, 23 Feb 2006 07:35:29



Quote:
> I'm designing a new high tech launch controller.  I have one question
> concerning continuity checking.

> I plan to use a very low current continuity check, on the order of 1
> microamp (.0000001 amps).  This should be low enough to safely test
> just about any igniter, including flash bulbs.

The system I've used for over a decade now does a continious continuity
check using an audible piezo buzzer rather than an LED. That way I can hear
what I'm doing when at the pad. The current flow through a piezo is on the
order of 10ma, quite safe for any ignitor I've ever encountered.

The NARAM system (and its predecessor) also do low level continious
continuity check. From the LCO control, you've got continious readout on all
pads continuity status. It really helps keep track of what's going on.

One problem with going as low as you're suggestion is spurious continuity.
The old NARAM system used too low a current, and got all sorts of false
readings from high humidity conditions.

--
  Bob Kaplow   NAR # 18L   >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle:      http://nira-rocketry.org/Document/MayJun00.pdf
    www.encompasserve.org/~kaplow_r/    www.nira-rocketry.org    www.nar.org

        S&T is becoming this decades Steve Weaver!

 
 
 

Constant continuity checking

Post by Bob Kapl » Thu, 23 Feb 2006 07:42:07


Quote:

> more and more I see launch controllers being build with NO continuity
> checking.

> the club I belong to does not have any continuity checks and launches go
> just as fine if not better then launches I attend with continuity checked.

> I built mine this way also and it serve me well, and I never need fear a
> continuity check ignition.

> I mean why run current into an igniter if you don't plan to set it off ?

> Really, if the igniter you chose had continuity when you checked it outside
> the motor,
> why check it inside the motor and run any risk ?

To make sure it's connected properly to the launch system. To make sure that
the clips are clean and it's got a solid connection. So that the LCO can
tell it's ready to go.

--
  Bob Kaplow   NAR # 18L   >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle:      http://nira-rocketry.org/Document/MayJun00.pdf
    www.encompasserve.org/~kaplow_r/    www.nira-rocketry.org    www.nar.org

        S&T is becoming this decades Steve Weaver!

 
 
 

Constant continuity checking

Post by Glen Overb » Thu, 23 Feb 2006 08:01:28


Quote:

>Would it be acceptably safe to leave that current flow at all times?
>That way you don't need to push a button to test continuity?  It would
>also make it easier to see marginal connections, just keep at it till
>the light stays green...

Are you going to limit the current input to the igniter, or limit the current
on the detect circuit?

If you connect the +12v clip to the igniter, then connect the ground clip,
then leg go of the ground clip, dropping it onto the blast deflector, and if
the blast deflector is on a metal launch pad staked into the ground, will the
igniter fire?

I liked the arrangement on the LMR / HPR pads at the McGregor NARAM a few
years ago:  A 3-way switch:  ON, OFF, Continuity.  When I was at the pad, I
could turn the switch OFF and the LCO could not mistakenly fire the pad.
Continuity was only on when it was on.

Chris Kraft wrote in his book that during the Gemini program, NASA learned a
lesson to leave things (like thrusters) powered off when they were not needed.

Glen Overby

 
 
 

Constant continuity checking

Post by Cranny Dan » Thu, 23 Feb 2006 10:48:15



Quote:
> To make sure it's connected properly to the launch system. To make sure
that
> the clips are clean and it's got a solid connection. So that the LCO can
> tell it's ready to go.

Hi Bob,

at our last club launch before winter, the club launched over 300 rockets in
one day.

no continuity checks needed, as their GSE does not do it, on purpose.

 
 
 

Constant continuity checking

Post by heninge » Thu, 23 Feb 2006 13:18:03


I'm not a big fan of continuity either. Check your igniter before you head
to the pad, may save you a trip back for a good one.

One thing I will share, We had a small grass fire (not uncommon in AZ) due
to a mis-fire on another pad that burned and shorted the wires to my
controller. My wires were running past this pad and no one noticed they were
burned. Fortunately I am in the habit of checking the for continuity to the
clips before hooking them to the igniter by touching them together and I saw
a spark. I am planning on adding an buzzer at the pad that will sound if the
line gets shorted again.

Before anyone freaks about the grass fire we do cancel launches if the
danger is too great. We take all fires very seriously in AZ.

Bob Heninger
Glendale, AZ


Quote:
> I'm designing a new high tech launch controller.  I have one question
> concerning continuity checking.

> I plan to use a very low current continuity check, on the order of 1
> microamp (.0000001 amps).  This should be low enough to safely test
> just about any igniter, including flash bulbs.

> Would it be acceptably safe to leave that current flow at all times?
> That way you don't need to push a button to test continuity?  It would
> also make it easier to see marginal connections, just keep at it till
> the light stays green...

 
 
 

Constant continuity checking

Post by Bob Krec » Thu, 23 Feb 2006 23:15:49


1 uamp is way too low.  You should be able to use 10 ma safely for any
continuity tester.  If you can't, the igniter is far too sensitive.

Check out the specifications for your ignitor (if they exist).  All
professional ignitors have a specified no-fire and all-fire current
rating.  The common Estes ignitors have a 2 amp all-fire rating and
their continuity checker uses 50 ma for the check.

The old daveyfire N28F has an all fire rating of 1 amp and a no-fire
rating of 0.4 amps.  You could pass 0.4 amps through the igniter
indefinitely!

Using a very low currents in the uamp range is likely to give a lot of
false readings simply due to leakage.  You are definitely best using
currents in the low ma range to prevent this.  A simple piezo buzzer in
series with the igniter usually limits the current to ~ 10 ma.  A 1K
resistor in series with a led will also limit the current through the
igniter to ~10 ma, as will the piezo buzzer in series with a led.
Copperheads, Quickbursts, all e-matches and dipped igniters that I am
aware of will not actuate witha 10 ma constant current.

Bob Krech

 
 
 

Constant continuity checking

Post by Bob Kapl » Thu, 23 Feb 2006 23:36:18


Quote:

> I liked the arrangement on the LMR / HPR pads at the McGregor NARAM a few
> years ago:  A 3-way switch:  ON, OFF, Continuity.  When I was at the pad, I
> could turn the switch OFF and the LCO could not mistakenly fire the pad.
> Continuity was only on when it was on.

I hate pads with this type of switch. Quite simply, people forget that they
are there. So they connect up their clips without turning the switch off. Or
they turn it off, then forget to turn it back on, which causes a long HOLD
before that pad can be fired.

--
  Bob Kaplow   NAR # 18L   >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle:      http://nira-rocketry.org/Document/MayJun00.pdf
    www.encompasserve.org/~kaplow_r/    www.nira-rocketry.org    www.nar.org

        S&T is becoming this decades Steve Weaver!

 
 
 

Constant continuity checking

Post by Bob Kapl » Thu, 23 Feb 2006 23:39:28



Quote:


>> To make sure it's connected properly to the launch system. To make sure
> that
>> the clips are clean and it's got a solid connection. So that the LCO can
>> tell it's ready to go.

> Hi Bob,

> at our last club launch before winter, the club launched over 300 rockets in
> one day.

> no continuity checks needed, as their GSE does not do it, on purpose.

And how many times did someone press the button and nothing happened?

BTW, what club / event is this? When NIRA ran big MRFF launches on the
NARAM-33 site, we'd break 600 on Saturday, but never got enough people on
Sunday to get over 1000. IIRC we came close a couple times...

--
  Bob Kaplow   NAR # 18L   >>> To reply, there's no internet on Mars (yet)! <<<
Kaplow Klips & Baffle:      http://nira-rocketry.org/Document/MayJun00.pdf
    www.encompasserve.org/~kaplow_r/    www.nira-rocketry.org    www.nar.org

        S&T is becoming this decades Steve Weaver!

 
 
 

Constant continuity checking

Post by Cranny Dan » Fri, 24 Feb 2006 04:41:35



Quote:
> BTW, what club / event is this? When NIRA ran big MRFF launches on the
> NARAM-33 site, we'd break 600 on Saturday, but never got enough people on
> Sunday to get over 1000. IIRC we came close a couple times...

sent you a PM
 
 
 

Constant continuity checking

Post by Wayne Johnso » Thu, 02 Mar 2006 06:16:43


The reason I'm pushing the low current is that long ago, I had a friend
use flashbulb ignition (a flashbulb and several segments of jetx wick)
on a clustered D Saturn V.  The LCO ran a continuity test (this was an
Estes launch controller) and the flash went off.  Steve was standing a
few feet away and couldn't hear for several hours afterward.

I just want to prevent incidents like that.