I'm performing tests of the detector's breakout electronics. These are printed circuit boards that will take signals from inside an ionization detector to the rest of the data acquisition apparatus.

The key component of these circuits is a capacitor, upon which charge is collected which induced a voltage across the capacitor. This charge is the result of ionization events inside the detector, and specifically the ionized electrons being collected by wires inside the chamber.

I have a BNC Model BH-1 pulse generator (link) and I have tried hooking it up directly to the circuit boards in question. The output from the boards, viewed on an oscilloscope, is signal-like, and responds to manipulation of the pulse generator dials, as one would expect. But it's heavily warped by the interference of the two involved RC circuits.

The pulse generator doesn't simulate the expected charge collection correctly. I want it to produce a charge buildup on the capacitor as a real event inside the detector would. Perhaps I require additional circuit components to make this work? Or I don't understand the problem myself in full detail? Any help or identification of my points of ignorance would be appreciated.

  • $\begingroup$ You might be better off asking your question on Electronics Stack Exchange? electronics.stackexchange.com $\endgroup$ – Farcher Jul 4 '17 at 5:43
  • $\begingroup$ @Farcher Maybe. You're likely to find real experts on the tools and process there, but they are unlikely to know the domain. $\endgroup$ – dmckee --- ex-moderator kitten Jul 4 '17 at 14:55

I'm pretty far from my expertise on this, but you seem to be overlooking (or at least not talking about) some of the tools you should be using, as you prototype.

Designing, prototyping and refining the close-to-the-detector electronics is a bit of an art, partial because of the problem that you are encountering: it's tricky to bench test this stuff. Just from sitting through a lot of talk I hear about three or four basic tools of the trade.

  • Time dependent simulation. It's a program, so you can send it arbitrary signals. Send it one that approximates the expected signal.

  • Bench testing with simple signals. Use a pulse generator and simple input waveform(s) (what you've been trying, I think). But, compare the results to what your simulation says to expect from a simple input rather than hoping that the output will look the same as the output from a real signal. (Even a digital output can be expected to show different thresholds and delays if nothing else.)

    This doesn't really test the circuit, it tests the simulation. But if you are to make heavy use of the simulation you need to have confidence in it.

    Vary the pulse length and strength (total charge).

  • Test the prototype electronics on the prototype detector It's generally the case that someone is building a miniature version of the proposed detector at the same time that the electronics are being roughed out. Take some of your kit to theirs and put them together.

  • Digital waveform generators This is the thing that you are asking for. You can program it to provide a pulse that approximates what you expect from the real detector. But you have to know what you are going to get from the detector to program it correctly. Now, there is a lot of experience with most classes of detectors so there are people to ask early on, and you can also ask the guy building the prototype detector to measure some signals for you (in, say, a digitizing oscilloscope).


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