pulse counter

It's probably a trigger level problem.

I don't think B&K actually makes anything any more... they jsut rebrand it.

John

rs

Oh it doesn't seem to be a trigger level problem. All the pulses are the same height and width.... how can you screw that up? The average value of the count rate is fine. There are just not enough counts out on the wings. You've got to record a bunch of numbers, plot them up and look at the statistics.

I figure who ever designed the thing no longer works there and no-one can answer my question. (They have no idea how it works.) We can build our own pulse counter, but that just costs a fortune when we're only going to sell ten or so a year.... I'd really like someone else to do it. Still at least then we=92d know how it works.

There are Nim bin and Camac things that can count pulses but those prices seem over the top too. (You've gotta buy the bin after all.)

Sigh, George H.

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Email me or call me at 512 339 9020 if you're interested.

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On

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Hi John, Well that may be one solution. Problem is we really don't sell many units. So price is a bit sticky... I have no idea how much you charge for such a relatively simple design. The counter hangs on the end of ths piece of apparatus.

We sell maybe 20-30 a year, and hope to go on selling it for many more. Many schools already have counters and so perhaps only 1/2 of the users need to buy a counter.

The two slit is not my baby and my boss is responsible for most of the 'upkeep' of the instrument. He's still sort of flaiing around, trying to decide what to do.

You can email me at, snipped-for-privacy@teachspin.com

I could give you some simple specs and maybe you have some idea of a 'ball park' price.

George H.

Red Lion Controls 'sub-cub' counter is a kind of panel-meter module that does simple counting. It might simplify the build-your-own option.

Are you accounting for pile-up effects at high count rates?

Thanks Whit3rd, the 10kHz count rate won't cut it.

It looks like we're just going to build our own. Turns out the boss was never happy with the discriminator on the current module. So we'll put our own threshold level into the front end and detect ~100mV pulses and not the TTL's. I was going to use a LM393 comparator, which I've used before. So at least we'll be adding a bit of value. A co-worker wants to squirt the count number out a usb port, which sounds like a good idea. (Hmm, I'm going to have to understand how that works.)

George H.

I think the "new" type you are trying to avoid is typically called "intelligent counter" or words to that effect. So you might want to look at manufacturers that offer both "intelligent" models, and other models that don't claim to be intelligent.

A quick Web search for "cheap frequency counter" turned up the Instek GFC-8010H at $175.50 from (in the adevertising sidebar on the right panel of the Google page). The same company offers 2 other Instek models that claim to be "intelligent", so I assume that this one is not. (But I don't know for sure.)

Best regards,

Bob Masta DAQARTA v5.10 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI DaqMusic - FREE MUSIC, Forever! (Some assembly required) Science (and fun!) with your sound card!

rs

Thank Bob, my Boss has looked at a whole bunch of different commercial units from Protek, B&K, I'm not sure if we looked at any from Instek. It looks like we are going to build our own. At least then we know what is going on inside.

I was playing with a LM393 (dual of the LM339) today. These are a bit slower than I'd like. Any favorite compartors with perhaps a 50

-100nS response time? LM311?

George H.

it seems to me that frequency counters are for measuring singals that have a frequency that can be measured un Hz. the randomly distributed pulses from a photomultiplier or a geiger tube can't.

what do you expect for less than 25c :)

LM319 is at slow end of that range.

hit an online electronic supplier site like digikey, newark, or mouser type "comparitor" into the search box and pick your desired parameters

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I tried it on DigiKey and got back "No records match your search
criteria."

How can that be???

JF

Try "comparator". ;-)

Have a look at Analog Devices - they have a couple with TTL or CMOS outputs with 7 - 8 ns propagation delay.

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Back about 25 years ago, I tried the LM311 as video amplifer to feed a TTL input CRT monitor. More like 200 nS, as I remember. (Replaced it with a NE592 video amp).

One of the oufits in Florida (Optoelectronics or one of their competitors) used the LT1016(?) comparator as the input for one of their frequency counter kit projects in Radio-Electronics magazine back in the '80s. I think it's good for 20 nS.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

It's about 500 kHz (that 10 kHz number was 3V worst case value).

Yeah, the counter is a tad underpowered. Most micros (the PICs in particular) are weak on counter functions. Best bet is something with a true counter/timer module, and some preprocessing to take out pile-up like an up/down pre-counter. Clock UP on input signal, DOWN iff nonzero, in synchrony with a local clock, incrementing the slow counter at a steady rate... a couple of stages of

74F193 can gobble lots of pulses fast, and disgorge at a compliant rate to the main counter. Your CPU count is only correct after the pre-counter finishes unloading, of course.

Thanks Peter, I was thinking today that maybe the spec I care about is the slew rate. I'd like it to get to 5V in about 100nS.. 50V/us. I don't think I care too much about the propigation delay. (But I could be wrong... I've only used the slow lm393 for switching low frequency stuff

Ahh 500kHz on the red lion... that could almost do it. I should have looked at the specs more carefully. 1 MHz is the maximum needed count rate and most of the time it's counting 100's of pulses a second.

You mentioned 'pulse pile-up' before, But I don't know exactly what you are talking about. At high count rates I'll sometimes have two pulses arriving at time's that are below the resolution of front end. I'll just count these as one event. But you seem to be impling some pile up at the counter. Will this be a problem at a mximum 1MHz count rate?

Thanks,

George H.

Yes, basically that's it. The pulses (300 ns) can be too close together for the counter to resolve, and a (say 100 kHz) counter might need a wider pulse or spacing. 100 kHz applies to 50% duty cycle clock, i.e. 5 us pulses, with 5 us spacing. Fast counters (74F193 does over 100 MHz) can handle the 300 ns pulses, and down to 5 ns spaces between pulses. The dead time of the system is then calculable, instead of being unknown and unknowable.

The average frequency is misleading in terms of the individual random times of pulses... and the market for 'frequency counters' doesn't support the timing requirements of pulse counting with appropriate specifications.

OK thanks, The existing front end elecronics gives a pulse with ~100ns rise time and >300ns fall time. (Kinda crappy for a PMT,) And I'll live with that. Most of the time the counting rates are really low... 10's to 1,000's per second. At high rates there is some error due to pulse overlap... we'll just ignore it.

George H.