Measuring the Voltage of a Spark

[Mad Phil]

Hi All, I've recently been working on a project testing the controller boards that are found in combi boilers domestic gas boilers. Most of the testing processes have been worked out but i'm still having problems testing a spark voltage as i have absolutely no idea how go go about this, so if anyone has any ideas that would be most appreciated.

Thank you for all your suggestions and it has given me food for thought.

Basically I'm trying to determine if the spark unit is good or on its way out, so really it would be a ball park reading not an exact voltage reading which would then go into a microcontroler.

[Marco]

AFAIK oven/boiler ignition transformers can do 10+ kV and the spark is going to be a high frequency signal, to know it's peak voltage I think you'll be wanting a MHz bandwidth divider/probe or better. So a 20+ kV MHz+ scope probe and a scope, or a fast peak detector (designed with input impedance similar to a scope) with a meter if you're only interested in the peak voltage (a multimeter built in peak detector does not qualify as fast).

[dr.diesel]

How accurate of a measurement do you require?  You can get a rough idea by measuring the spark gap distance.  There are several key variables that influence this, ambient pressure, humidity, etc, but will get you in the "ball park".

http://www.kronjaeger.com/hv/hv/msr/spk/

[KD0CAC John]

Automotive KV meter .

[Neilm]

Breakdowns (sparks) are very hard to measure accurately. They are very short term events - what you see is probably due to persistence of vision rather than the sparks presence. Not only do you need fast responding equipment, you also have to remember that the breakdown is a broadband artifact. It is what was used in early Morse transmitters. So any results you do measure could be affected by the EMI this generates and ruin the result.

So look at getting something that is properly designed to do this, rather than trying to make something.

[NiHaoMike]

Just add a second spark gap in series with the first and see how much margin is left.