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From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: Pulse Height Measurement
Date: Wed, 22 Jan 2003 02:46:39 GMT
NNTP-Posting-Date: Tue, 21 Jan 2003 18:46:39 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
John Devereux wrote:
> Greetings to all you fine SED folk.
> I am looking or ideas in the area of pulse height measurement. We
> have an instrument which produces a noisy background signal (1/f
> noise), with pulses superimposed on it whose "height" we wish to
> ____________________ ___
> ' ' ^
> ' ' ' ' |
> ' ' ' ` Pulse Height
> -- ' ' `` ` - |
> ` ' ' ` v
> `-- _________________________ __
> The pulses can be from a few mV to a few V, and arrive randomly.
> The duration is ~10-100 microseconds, (but faster would be nice).
> We currently do it in software, digitizing the signal and using
> an algorithm which involves tracking the minimum and maximum
> excursions of the signal, and deciding when the fluctuations
> constitute a "pulse".
> I would like to implement this in hardware, so that we can get
> faster performance with a slower microcontroller.
> My initial thoughts are something like this:
> | | |\
> | D1 C1| | | | \ Diff Amp
> Signal| === o|___ R1 | \ ___
> ------| 0V__| o| | |U1 \___o o______ -->ADC
> | | C2| |Reset +--- | / |Sample |
> | | === | | | | / | |C2
> | | D2 | | R2 | | / | ===
> | +-|<|-+--------+------+-------|-/ | |
> | | | | |/ | 0V-----
> | -R4-- | | ___+5V
> | | | |
> | | | U2 _ 2k2
> | | ___ `-----|+\ |
> | | | \ | -----Sample
> | | |DAC --------|-/ | Irq
> | | |___/ Set |
> | | Threshold |
> | | _ |Comparators
> | `----------------|+\ |
> | U3| -'
> D1 and D2 are magic diodes with 0V forward drop.
> C1 and C2 store the maximum and minimum excursions of the signal.
> however R3 and R4 force the long term values to track the input.
> (Otherwise a step change in input can leave the circuit waiting
> forever for the end of the "pulse".
> The sample interrupt is triggered when the difference between
> maximum and minimum (="the pulse height") exceeds the threshold,
> AND the input signal has returned to half the pulse height. (so
> we know the pulse is over, and didn't just have a momentary
> wiggle in it).
> The microcontroller operates the sample gate, the reset gate, and
> starts the ADC conversion.
> What's the best way to do this stuff?
> John Devereux
Haven't you heard of the kick sorter (the first way to do this in
The pulse was amplified and stretched so it could drive a solenoid,
moving a lever that threw a ball.
The larger the pulse, the farther the ball would go; catch columns
were set to gather the balls that were thrown at specific distances; a
Noise would integrate out, producing a level (equal) plot and the
pulse amplitude spectrum would "rise" above that "floor".
All metal; *true* solid state.
"Electronic" solution: sample the pulses and store them in locations
related to the amplitude.
This is called a pulse height analyzer; standard physics equipment for
well over 30 years.
Snoop around electronic surplus stores and get one; that way you do
not have to buy and/or design/build expensive stuff and do not have to
Some of the equipment has output(s) that are ameanable to data
collection from a PC.
There are PC plugin boards (with software) that can do this as well.
Look at your pocketbook and choose an option.
Most of these pulses that are analized are in the nanosecond region.
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