17 replies to this topic

[MFX]

Just had a result on EBAY :-
Amptec 620A4

Failsafe resistance meter. More info :-
http://www.amptec.co...heets/620A4.pdf
http://www.amptec.co.../A4optionNP.pdf

Also for any techies building their own test equipment there are some details of the failsafe current source here:-

http://www.amptec.co...ets/630ESfs.pdf

Martin.

[BrightStar]

Looks like a very good bit of kit. Couldn't follow the Ebay link - how much did you pay? Nice how they get such high precision with fairly low currents. I'm sure it will impress paying customers

I always hesitate (and stand well back) when testing continuity with a cheap multimeter. I'm thinking of making up some test prods with 100 ohms of resistance built in just in case the DMM gets dropped and decides to short its PP3 across the terminals

Edited by BrightStar, 30 August 2007 - 10:00 PM.

[MFX]

Looks like a very good bit of kit. Couldn't follow the Ebay link - how much did you pay? Nice how they get such high precision with fairly low currents. I'm sure it will impress paying customers

I always hesitate (and stand well back) when testing continuity with a cheap multimeter. I'm thinking of making up some test prods with 100 ohms of resistance built in just in case the DMM gets dropped and decides to short its PP3 across the terminals

Paid about £150 (depending on whether C&E get interested in the import) New they're about £1000.

Good idea about the resistor in the test probes. Other ways to quickly check a cheap meter before sticking it on live pyro are to stick a bare igniter across it first (I always have one in a box in my toolbag) or much cruder, stick the probes across your tongue if you get more than a barely noticeable tingle dont use it!

[Arthur Brown]

I know one pro pyro tecnician who uses the Maplin cheapy meter ( N20AX ) price varying from £5.99 according to sale lists! Yes his is checked with a bare igniter.

He tests every setup before he considers it ready to fire. Part of his prep is to calculate the resistance he expects for each cue - If the real resistance is not the same he will recheck the wiring and connections.

While the approved failsafe tester is best, it is expensive enough to deter prospective purchasers. As a general rule digital reading multi meters are probably worth testing with an ematch and swing needle ones not so.

When you know what your controller will safely fire, you can measure that all the circuits are within that.

[MFX]

While the approved failsafe tester is best, it is expensive enough to deter prospective purchasers. As a general rule digital reading multi meters are probably worth testing with an ematch and swing needle ones not so.

I would say test ANY meter regardless of whether it's display is a needle or digital, they can both fail. If a meter is dropped (maybe without your knowledge) how do you know what damage may have been done internally?

The other advantage of dedicated low ohm/pyro meters is that they can measure milliohms. So to an extent parallel igniters can be tested, simply short the bell wire at the igniter end and measure the bell wire resistance, then remove the short and measure again and subtract the bell wire resistance. You should now be able to get a good idea of how many parallel igniters you have connected.

[Arthur Brown]

I agree with you! However from experience on a pyro course where several people had problems with the concepts of series and parallel and disasters trying to arrange igniters in series for an excersise. Several people wouldnt understand series, parallel, or digital meter. The higher error analysis is beyond many folk.

The maplin digital meter at £6 is a good start, test it for malfunction with a bare ematch on a short wire.

[marble]

A DMM wont pop a ematch

My DMM's output doesn't exceed 0.2v and the maximum currant would be under half a milliamp

Paying £150 for a expensive multimeter just to test e-matches is crazy

Edited by marble, 06 September 2007 - 10:40 AM.

[MFX]

A DMM wont pop a ematch

My DMM's output doesn't exceed 0.2v and the maximum currant would be under half a milliamp

Paying £150 for a expensive multimeter just to test e-matches is crazy

A CORRECTLY FUNCTIONING DMM won't pop an Ematch, but does your DMM have a failsafe current source? does it have a means of checking that the the output current is a safe level? Do you know how the wires are routed inside/what would happen if the wire to the PP3 battery inside it (which CAN pop an Ematch) came adrift and ended up somewhere it shouldn't? If you've ever opened up a DMM you'll know that the power, range selecting etc. is generally done by a horrendously complicated circular arrangement of PCB tracks and wipers on the range select knob. Some of those tracks carry full battery voltage (depending on the meter), do you have anyway of knowing what would happen if one of those wipers came adrift from the plastic knob (something which has happened on cheap meters I've owned) and shorted the wrong tracks? Another operational benefit as I've already pointed out is the ability to check parallel igniters which a cheap DMM can't do. Besides £150 is cheap for a professional pyro company.

[YT2095]

another way is to send a frequency down the wire at the ignition end, and then use a Dip Meter to walk along that wire path, any breaks or errors will show up quite nicely.
Telephone engineers use something similar too.

Edited by YT2095, 06 September 2007 - 05:12 PM.

[MFX]

another way is to send a frequency down the wire at the ignition end, and then use a Dip Meter to walk along that wire path, any breaks or errors will show up quite nicely.
Telephone engineers use something similar too.

We actually use one of those, but we mainly use it for identifying bell wires that have some how got mixed up between the field box and the pyro Clip the tone generator on at the field box end and use the tone probe to find the other end. It also means that if you have several long runs of several hits you can simply run all the bell wires out at the same time by putting the rolls on a stick, and then identify them by using the tone probe.

[YT2095]

neat!
and Much better than using a Megger

[marble]

A CORRECTLY FUNCTIONING DMM won't pop an Ematch, but does your DMM have a failsafe current source? does it have a means of checking that the the output current is a safe level? Do you know how the wires are routed inside/what would happen if the wire to the PP3 battery inside it (which CAN pop an Ematch) came adrift and ended up somewhere it shouldn't? If you've ever opened up a DMM you'll know that the power, range selecting etc. is generally done by a horrendously complicated circular arrangement of PCB tracks and wipers on the range select knob. Some of those tracks carry full battery voltage (depending on the meter), do you have anyway of knowing what would happen if one of those wipers came adrift from the plastic knob (something which has happened on cheap meters I've owned) and shorted the wrong tracks? Another operational benefit as I've already pointed out is the ability to check parallel igniters which a cheap DMM can't do. Besides £150 is cheap for a professional pyro company.

And what are the chances of that happening? same thing could happen with your expensive DMM, mains wire could come loose, transformer could malfunction, wiring could come loose etc

Im not using some cheap shit meter, it passes all legal standards for working with mains wiring here and cost a fair bit ($80) so i feel completely safe using it. Even my cheap multimeter's have exceptional build quality.

[MFX]

And what are the chances of that happening?

25 Feb 1987
Explosive: Flare
Event: Explosion
Activity: Testing
Location: Manufacturing Site
Fatalities: 0
Injuries: 0

An operator experienced a problem with a flare training aid.
She took the maroon to another room and used a continuity meter to check it instead of a safety 'o' meter.
During this procedure the maroon activated.

Crown copyright
EIDAS Database


Unfortunatly there is no more detail than that

[marble]

Each to his own, but i still like my odds

[pyrotrev]

I built an ohm meter incorporating a safe current source into my firing panel, the latter was quite simple using a series resistor and clamping diode to make sure if the constant current generator went wrong, you could never exceed 10mA through the igniter. If you use premade cables you can calculate the likely resistance of the parallel/series igniters and then put those on the cue sheet for checking. It's saved a few embarrassing moments where stuff has been plugged up wrongly or there's been a dodgy contact. Also means you can do ALL the testing remotely, giving a further safety margin.