Electronic Flash Testing and Equipment?

[Ralph Javins]

Q1: are you using the photo-diode in voltage mode, or in current mode?
(the response times might be different)
Q2: flash duration on a digital storage scope sounds ok, if you are using a
period/frequency counter, you need to define a precise triggering level, this
might be very difficult to set?

if its getting too technical, you can also reply per pm. thanks.

Good morning, Lynux;

For the measurements we are taking in this application, the difference in the timing resulting from the way that we are setting up the test (voltage mode or current mode) will not be that significant. We are looking at something that will be measured in the region of a few milliseconds -- single digits -- and the response time of the phototdiode is at least in the microsecond range, if not nanoseconds. That is at least three (3) orders of magnitude different than the minimum response time of the testing unit element. If we are looking at the 10% level for our trigger and measurement points, we are definitely in milliseconds. If we are looking at the 50% level, then we will probably be down in the one or two millisecond range with an electronic flash unit at full power with a full dump from the flash capacitor. If we are looking at a partial power flash, then we may be down around 50 microseconds probably at the shortest. Then we might start looking at the effects of the timing capabilities of the components we are using. The 10% point and the 50% point seem to be the two levels where the photoflash people measure the duration of their electronic flash units. In this application, I do not think that we are approaching any real limitations of our test equipment. I know that my oscilloscope is rated to go to 200 Mc, so that will not be a limitation in showing the light output curve.

In any case, I am still interested in suggestions or references on how to test these things. I have worked in electronics all my life, but I admit that I am not really familiar with testing techniques for electro-optic devices.

I do admit that I am going by my memory of the specifications from the middle 1960s for the response time of the 1N2175, but I have not yet been able to locate a full data sheet for the photodiode. My TI Data Books from that time period disappeared with the death of a marriage.

[Sethasaurus]

You will easily be able to measure a pulse of the order of milliseconds with your average soundcard.
You will amost certainly be able to capture and measure the trace on a halfway decent scope.

The old quote holds true - "Can't never could".

[Nicholas Lindan]

If you want to measure time accurately with a photodiode you are going to have to reverse bias it and measure the current.

A 10K resistor for current sensing and a 9v battery for reverse bias will work, as will many other arrangements.

I don't know of any working EEs who still maintain a bookcase of old data books.

A '2175 is an old, old part. You might want to try something a bit more modern like a BPW34 [not all that modern, TTtT] or an OP950 if you want something faster.