Continuity Check at the Pad

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Zonie

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I've noticed a lot of folks, including the several clubs that have torture racks check the continuity at the pad.

I Guess there are two camps in this topic. Check at the pad or minimum safe distance (MSD). I prefer to do it at the MSD. My thinking is that if you have an anomaly like a shorted relay, Very low current igniter, flakey igniter, shorted indicator (LED, Lamp, Buzzer, etc.) you could have the ignition right now, when you are at the pad. Can ruin your day.

The current wireless systems naturally have this feature, as do some wired and club systems I've seen. You never know what someone will show up with at a launch igniter-wise, and using club pads can create a situation that is unsafe in this situation.

What D'yall think?

Being a member of a club that does not use club racks, We bring our own. My current setup is 15 years old and the Cable is getting a bit worn, so I decided to go wireless myself. I've got two basic concepts, one with a transmitter at both ends, and one simpler concept that uses very bright led's and sound so you can see/hear the indicator from the MSD. The latter more appropriate for LPR/MPR.


Waiting for my modules to arrive to work out the concepts. Gotta love the wireless stuff you can get from Hong Kong these days.
 
I've never been to a High-Power Launch in Hobby Rocketry, so I can't really speak about the Pad part of it, but I have been around a few Controlled Detonations, and thus would say that I'de be in the Camp of checking Continuity from MSD. Safety First, Every Time!
 
I too eventually want to have a Wireless Setup so that I can launch a MD 29mm With a Spool of Wire to trigger a lightning Strike.

A friend of mine was killed by Lightning, and I've been afraid of it ever since then. If I can trigger a Lightning Strike, it will likely make me feel better.
 
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I too eventually want to have a Wireless Setup so that I can launch a MD 29mm With a Spool of Wire to trigger a lightning Strike.

A friend of mine was killed by Lightning, and I've been afraid of it ever since then. If I can trigger a Lightning Strike, it will likely make me feel better.

Talk about minimum safe distance...:y:


[video=youtube;34NpyA2OuaE]https://www.youtube.com/watch?v=34NpyA2OuaE[/video]
 
I Guess there are two camps in this topic. Check at the pad or minimum safe distance (MSD). I prefer to do it at the MSD. My thinking is that if you have an anomaly like a shorted relay, Very low current igniter, flakey igniter, shorted indicator (LED, Lamp, Buzzer, etc.) you could have the ignition right now, when you are at the pad. Can ruin your day.

Pad circuits should be designed so that it requires more than one failure to get an unsafe current.
 
Pad circuits should be designed so that it requires more than one failure to get an unsafe current.

Like What? A shorted LED would allow full current even with a resistor.
 
Like What? A shorted LED would allow full current even with a resistor.

A shorted LED would still have the current limited by the resistor. On the other hand if the resistor fails to a short then you get lots of current until the LED fails.

But if you are using a 1K series resistor to limit current to the LED, just use two 500 Ohm resistors in series. Now if one fails you will get twice the current but it will still be safe. Assuming that twice the normal test current is still safe of course.
 
Ahhhh, I'm in another camp. I don't feel the need to test at the pad. Before I connect the igniter, I slap the ends of the wire together to see if there's sparks. Places I go don't use clips and just bare wire to twist to the igniter.
If there are no sparks, ie. busted relay or what have you, I attach the igniter and go back to arm the pad. I don't feel the need to check continuity at all. If the igniter is bad, I go out and put a new one in. The extra time doesn't phase me. Kurt
 
Yeah, I was thinking of using multiple resistors just for that reason.

I keep a 12V Auto lamp at the pad to test for fused contacts and to troubleshoot pad issues when others use my pad... That usually end up as igniter issues. :facepalm:
 
Our club equipment is only used at BALLS. When it was made we told him not to have a continuity check. You never know what kind of igniters will be used. We don't want something bad happening with an O motor.

Clips-- we have best intentions to have clips on the wires. For some reason flyers think igniter wires an inch out of the nozzle is OK. We bring rolls of wire, ask for a piece to save the equipment.

M
 
Yeah, they are little tiny blast deflectors, ain't they?
 
I believe that a high power launcher without a continuity check is a hazard. I want to know if the relay contacts are welded closed and powered before I connect my igniter and I can't do that without a continuity check circuit.

A proper pad continuity check circuit should have an LED, piezo beeper and a resistor in series to limit the current to not more than 20 ma which should be is a safe current for any igniter used on a high power rocket. Any igniter that can't be continuity checked is itself unsafe and should be prohibited from use.

Bob
 
I believe that a high power launcher without a continuity check is a hazard. I want to know if the relay contacts are welded closed and powered before I connect my igniter and I can't do that without a continuity check circuit.

A proper pad continuity check circuit should have an LED, piezo beeper and a resistor in series to limit the current to not more than 20 ma which should be is a safe current for any igniter used on a high power rocket. Any igniter that can't be continuity checked is itself unsafe and should be prohibited from use.

Bob

I don't care what's used for continuity. I slap the wires or clips together several times. If there's sparks, there's a problem. I've considered a small pocket meter too. The real big issue I have is those who use igniters that are close to being ematch based.
If so, if the system isn't designed for it, a launch could occur with a continuity check. Not good if people are standing close to a large motor.

Another good test. Connect your igniter to the system away from the motor. If it goes off, there's a problem relay or otherwise. You don't need a continuity circuit Bob, it's a convenience only. As long as the powers that be test the continuity circuit out on ematches and they don't pop it sure will be safe with standard nichrome jobs. If I don't know the status of a given system, I proceed with caution and once I "clear" the circuit to attach the igniter, I don't feel the need to "test" continuity thereafter. Kurt
 
you could have the ignition right now, when you are at the pad. Can ruin your day.
What do you mean? I've always wanted to know what it would feel like to lie down underneath an M motor coming up to pressure... :D

But seriously though - our club launch system (wired) has continuity checks at the relay boxes for each pad. I almost always use them, but I also use my own igniters (NOT low current either) which I check with a multimeter beforehand so I know they'll fire anyways...
However, my personal launch controller (also wired) does not have a continuity check built in - don't really care and not worth the trouble IMO.
 
But seriously though - our club launch system (wired) has continuity checks at the relay boxes for each pad. I almost always use them, but I also use my own igniters (NOT low current either) which I check with a multimeter beforehand so I know they'll fire anyways... .

The purpose of the pad check is to check the connection to the igniter, not the igniter. Damn dirty clips. :)

As for low current igniters, there is a reason why the NASA Standard Initiator can pass a five minute test with 1 Watt of input power while doing nothing.
 
The purpose of the pad check is to check the connection to the igniter, not the igniter. Damn dirty clips. :)

As for low current igniters, there is a reason why the NASA Standard Initiator can pass a five minute test with 1 Watt of input power while doing nothing.
Agreed. If you have large launches like CMASS does with 50 or more launches an hour you can't afford to have continual failures due to dirty clips or igniters with open bridgewire. That's why a continuity check circuit is important on all pads. We make our launch equipment, and have verified the standard continuity check circuit we use is safe for all known hobby ignition systems including flash bulbs. I've been with the club for 15 years and during that time we have launched over 50,000 rockets and not one of them has ever been launched on the continuity check......:rolleyes:

A 20 ma maximum continuity check current should not activate any safe hobby rocket igniter. P <= I V = 0.02 x 12 ~ 0.25 watts. If you have a low current piezo beeper in series with a LED and a > 560 ohm resistor, the current will be ~ 10 ma and if any of the 3 devices short the current will not exceed 20 ma......

If you have any doubts about a continuity check circuit, you should test it with your igniter before you insert the igniter into the motor. The worst case scenario then is you burn the igniter if the circuit is not safe for your igniter.....but it's outside the motor so you don't have an accidental launch. And I can't say I've seen that happen with any club owned launch system......

Bob
 
Well I've been doing some testing, and I have breadboarded a two-way wireless controller which allows for remote power enable, arming, continuity check, and launch. The system needs two series relays to be latched to allow the launch button to sink the coil of the ignition relay to initiate full current path through the igniter.

Each relay lights specific LED's at the pad to tell the user what state the system upon approach.

I have test button to check for fused contacts in the launch relay to test it at the pad without resorting to slapping the clips together as you may not see sparks in the bright sun, although in 15 years, I have never had an automotive relay fuse, and the ones I have been using have over 500 launches on them.

It's a bit overkill on the safety side of things, but I figured what the hell. Double redundancy in the latching circuit is better than not.

I also have a wired circuit in it that can be used instead of the radios, so I can use it at a launch does not allow wireless systems by just adding a 4 conductor phone cable.

My continuity circuit has been tested with Q2G2's, Solars, First Fires, Copperheads, and E-matches with pulse and extended in circuit testing.

Two way comms have been successful for about 150 feet through several rooms in my house to standing down the street. Should go much farther with unobstructed Line of Sight.

Now to build the launch system and field test it.
 
Well I've been doing some testing, and I have breadboarded a two-way wireless controller which allows for remote power enable, arming, continuity check, and launch. The system needs two series relays to be latched to allow the launch button to sink the coil of the ignition relay to initiate full current path through the igniter.

Do you mind sharing a schematic (if you have it) of the pad-side circuit? I'm also building a controller and am interested in your safety features.
 
Here's a nice report on allowable max current for safe continuity checks of various ignitors. Found this just yesterday along with a few other nice papers on the same site:

https://www.psc473.org/howto/Igniter.pdf

Found it while considering a very small, dirt simple 1.5V at-pad continuity tester for BP clusters to allow individual ignitor continuity tests before connecting cluster adapter leads, all without bothering the LCO or involving a high current 12V firing system which does have the capability of firing the ignitors.
 
Nice resource. Like Bob mentions, if one connects the igniter outside of a rocket motor and it doesn't "poof", the relay isn't shorted. Push the continuity button and it doesn't poof, safe for that particular igniter. Kurt
 
Here's a nice report on allowable max current for safe continuity checks of various ignitors. Found this just yesterday along with a few other nice papers on the same site:

https://www.psc473.org/howto/Igniter.pdf

Found it while considering a very small, dirt simple 1.5V at-pad continuity tester for BP clusters to allow individual ignitor continuity tests before connecting cluster adapter leads, all without bothering the LCO or involving a high current 12V firing system which does have the capability of firing the ignitors.

That's a useful article, however it really does not address what is a safe current for a given igniter, because no timed measurements were reported. While it adequate for non-critical situations like launching a hobby rocket, a more stringent standard is required for military and civilian pyrotechnic initiation.

Professional igniters are tested to determine the all-fire and the no-fire currents. A number of igniter are tested to determine the range of currents and times require to activate the igniters. The results allow the determination of the no-fire current which is the maximum current that can be passed through the igniter for a given time, typically 5 minutes, and not have any of the igniters fire. Conversely, the all-fire current is the minimum current that must be delivered to fire all of the igniters within a specified time period. Once you have these limits, you can set a design factor for your circuit.

For example, if the igniter has a no-fire current of 1 amp, and an all-fire current of 3 amps, a specification for a firing circuit might be: 1.) the maximum continuity current shall be 25% of the no-fire current or 0.25 amps and 2.) the firing current shall be 200% of the all-fire current which would be 6 amps in this example. The purpose of this type of standard is that ordnance systems may be armed for several minutes before use and the operator must have an indication that a specific weapon is actually ready to go if and when he presses the fire button, and then when he presses the fire button, the device will be activated within a known time window.

Bob
 
That's a useful article, however it really does not address what is a safe current for a given igniter, because no timed measurements were reported. While it adequate for non-critical situations like launching a hobby rocket, a more stringent standard is required for military and civilian pyrotechnic initiation.
Thanks, that's all that I'm after, checking model rocket igniters already installed in clustered motors at the pad.

I thought I had some 1.2V LEDs on hand, but I don't know why I did as that's a lower Vf than any I can find referenced anywhere on-line. I'll have to go with 3V, either via two AAAs (easily found and cheep) or a CR123A or CR2032, much more compact, but harder to find and significantly more expensive from non-mail-order sources. I have both more compact types on-hand but don't have a single-cell CR2032 holder, unfortunately. I want to put this in a tiny plastic project box.

EDIT: I figured this must have been done before:

Build a Super Simple Safe Cheap Igniter Tester

https://www.apogeerockets.com/downloads/Newsletter287.pdf

but I don't like that one because it relies solely upon the current limiting of the LED (even though every LED I've destroyed during max current testing failed open, not shorted) and it looks like it's made for checking igniters prior to installation in the motor. Considering the Estes type igniters can be damaged during installation, that won't do. I want a daylight visible LED with a current limiting resistor in series, a proper momentary pushbutton switch, and a short length of 24ga speaker wire with microclips installed to put minimum stress on the installed igniters prior to attaching the cluster adapter lead.

Anyone done that sort of thing before? How else can one test parallel wired igniters at the pad without bothering the LCO and taking the risk with a system designed to actually fire the igniters? I don't trust series wired clusters for obvious reasons although I've read that the (currently unobtainium) Q2G2 clustered igniters wired in series are reliable.
 
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Professional igniters are tested to determine the all-fire and the no-fire currents. A number of igniter are tested to determine the range of currents and times require to activate the igniters.

The results aren't worth much now that the Estes and Quest igniters have changed, but I performed this testing a while back.
 
The results aren't worth much now that the Estes and Quest igniters have changed, but I performed this testing a while back.
Is your user name a reference to a response from "Clem" in a Firesign Theater sketch?
 
Thanks, that's all that I'm after, checking model rocket igniters already installed in clustered motors at the pad.

I thought I had some 1.2V LEDs on hand, but I don't know why I did as that's a lower Vf than any I can find referenced anywhere on-line. I'll have to go with 3V, either via two AAAs (easily found and cheep) or a CR123A or CR2032, much more compact, but harder to find and significantly more expensive from non-mail-order sources. I have both more compact types on-hand but don't have a single-cell CR2032 holder, unfortunately. I want to put this in a tiny plastic project box.

EDIT: I figured this must have been done before:

Build a Super Simple Safe Cheap Igniter Tester

https://www.apogeerockets.com/downloads/Newsletter287.pdf

but I don't like that one because it relies solely upon the current limiting of the LED (even though every LED I've destroyed during max current testing failed open, not shorted) and it looks like it's made for checking igniters prior to installation in the motor. Considering the Estes type igniters can be damaged during installation, that won't do. I want a daylight visible LED with a current limiting resistor in series, a proper momentary pushbutton switch, and a short length of 24ga speaker wire with microclips installed to put minimum stress on the installed igniters prior to attaching the cluster adapter lead.

Anyone done that sort of thing before? How else can one test parallel wired igniters at the pad without bothering the LCO and taking the risk with a system designed to actually fire the igniters? I don't trust series wired clusters for obvious reasons although I've read that the (currently unobtainium) Q2G2 clustered igniters wired in series are reliable.
The tester article explains why the tester works without a series limiting resistor. "Here’s a guaranteed safe design. Why? It is safe because the battery chosen for this project can only produce about 25 milliamps. The lowest current igniters I know about, the Q2G2 from Quest (www.apogeerockets.com/igniters.asp#Q2G2_igniter), need over 100 milliamps, so you have a wide safety margin."

The CR2032 Lithium battery is the most commonly used Lithium battery. It's used in most auto locking and starter remotes. You can get one at any auto parts/drug/hardware stores so they are readily available. In a convention circuit where the voltage supply has a low impedance (can push our a lot of current), you can convert the voltage to a current with a series limiting resistor (I = V/R). These batteries have an open circuit voltage of 4.2 volts so their internal resistance is R = V/I = 4.2/0.025 = 168 ohms. The bottom line is that as long as you use the CR2032 battery used in an auto remote you can't get more current out of the circuit. Change to another battery, all bets are off.

A simple way to determine the series limit resistor value is to invert the desired current to find the ohms per volt that will be necessary for your supply voltage. If I = 0.025 amps, R = V/I = V/0.025 = 40 ohms x V = 40 ohms per volt. Take this number and multiply it by the battery voltage and you have the resistance value you need.

Bob
 
The results aren't worth much now that the Estes and Quest igniters have changed, but I performed this testing a while back.
Dave, I don't think I've read anything you wrote that wasn't worthwhile. Whether the igniters are in production or not, you illustrated the a proper method to determine the all-fire and no-fire values and that is very useful.
 
Anyone done that sort of thing before? How else can one test parallel wired igniters at the pad without bothering the LCO and taking the risk with a system designed to actually fire the igniters? I don't trust series wired clusters for obvious reasons although I've read that the (currently unobtainium) Q2G2 clustered igniters wired in series are reliable.

I use a four wire Ohm meter. Commercial ones are usually a bit expensive and actual igniter testers even more so. So I built one
 
If your using a relay, then a safe relatively easy means of checking continuity would be to use a small programable IC with a very high value pull up resistor. Then allow the igniter to pull the pin low. Power your LED from another pin.

Now if you want to test to ensure the pull up didn't fail short (which I have never heard of) short the leads and ensure the LED senses it. If the pull up fails short, it will destroy the pin on the IC. Typically the can only sink about 35 mA.

But, if high power, I simply would have the entire box deactivated while making the connection. Stepping back to test isn't that big a deal to me.
 
The tester article explains why the tester works without a series limiting resistor. "Here’s a guaranteed safe design. Why? It is safe because the battery chosen for this project can only produce about 25 milliamps. The lowest current igniters I know about, the Q2G2 from Quest (www.apogeerockets.com/igniters.asp#Q2G2_igniter), need over 100 milliamps, so you have a wide safety margin."

The CR2032 Lithium battery is the most commonly used Lithium battery. It's used in most auto locking and starter remotes. You can get one at any auto parts/drug/hardware stores so they are readily available. In a convention circuit where the voltage supply has a low impedance (can push our a lot of current), you can convert the voltage to a current with a series limiting resistor (I = V/R). These batteries have an open circuit voltage of 4.2 volts so their internal resistance is R = V/I = 4.2/0.025 = 168 ohms. The bottom line is that as long as you use the CR2032 battery used in an auto remote you can't get more current out of the circuit. Change to another battery, all bets are off.
Great, CR2032 it is. Didn't realize the high internal resistance limiting max current factor. I have a number of CR2032s on hand. Now, to buy a CR2032 holder.
 
Do you mind sharing a schematic (if you have it) of the pad-side circuit? I'm also building a controller and am interested in your safety features.

I'll share it when I am satisfied with the entire thing. I'm still working out some details, and want to be sure there are no sneak paths or other anomalous issues with the RF parts.
 
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