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FREQ COUNTER help

P

Paul Taylor

Jan 1, 1970
0
Fred Bloggs said:
What are the part numbers and web links to the photometer and pad?
Hi Fred the photometer isn't supplied by me so im unsure on the full spec as
for the pad it is from Electron tubes Type AD7
 
F

Fred Bloggs

Jan 1, 1970
0
Assuming that the pulse-pair resolution means what I think it ought to
mean, Paul's counter won't have to deal with photon pulses narrower
than about 12nsec or occuring at a higher frequency than 41.7MHz.

In order to avoid problems from "pulse pile-up" the physicists who
devised the experiment probably set up the system for a maximum average
count rate of about 2MHz -

How did you make that leap into controlling the average rate at 2MHz?

the photons are almost certainly going to
appear at random intervals, and if the amplifier discriminator has a
dead time of 24nsec, the change of getting two photons within a 24nsec
period (and missing the second one) will be about 5%, at an average
rate of 2MHz which is manageable and correctable.

Poisson time of arrival lamda=2E6 mean events per second makes for two
to occur at something like 0.5(lamda*25n)^2 or 0.125% ? Or two or more
to occur at 0.127%.
 
F

Fred Bloggs

Jan 1, 1970
0
If I were to do this I'd probably try and do the whole thing in a
Xilinx Coolrunner II programmalbe logic part. As programmalbe logic
goes, these are relatively low power parts, with more than enough
bistables to realise a pair of 12-bit counters while fast. enough to
handle the 24nsec pulse-pair discrimination.

Newp- counter clock inputs are asynchronous to the system clock which
must be synchronized with the telemetry, so you're not going to get off
that easily, assuming you want to avoid bad data points entirely. Then
the OP states rate measurements to be made every other millisecond, so
two counters are not necessary.
 
K

Ken Smith

Jan 1, 1970
0
rick H said:
How do you know that the emission of these photons isn't bursty -
nothing for a while, and then 100 in a nanosecond? If that's the case,
your 10ppm guess is hopeless. You need to know the *maximum* expected
event-rate in order to determine the counter's maximum increment rate
and in order to know the accuracy of the ms clock required for +/- 1
photon "resolution".
k
Hmmmm ... maybe this calls for a flash ADC to estimate the number of
coincident photons and an adder instead of a counter.
 
J

John Fields

Jan 1, 1970
0
John Fields said:
It sounds like you need two counters, running more-or-less independently.
One simply counts up, every photon. The other counts up every millisecond,
at which time you read the current photon count (input the state of the
photon counter) and subtract from it the photon count at the last
one-millisecond tick; this gives you "how many photons were captured
during millisecond N", so to speak. With a micro, a millisecond is like a
year[1] - it'd be almost trivial to write some data-logging S/W that could
keep up with that.

---
Nope.

He needs one counter to accumulate the photon events and another to
generate the count enable for the photon counter, plus some glue
logic for the clear and the data read/latch (maybe).

It's doubtful whether he could generate the time base for the enable
with just a ?C since he needs something with an accuracy of around
10ppm to generate the enable window in order to get the +/- 1 photon
resolution he's looking for. Maybe less than 10ppm, that's just a
first cut look at it.

How do you know that the emission of these photons isn't bursty -

---
I don't, but so far in the discussion it doesn't matter. All I've
done is to describe a general-purpose EPUT counter which can
accumulate a maximum of 65536 hits before it overflows, which is
what the OP asked for. If he has issues with interpulse timing and
the like I expect that he'll bring them into the discusion where
they can be resolved. Or not.
 
R

Rick

Jan 1, 1970
0
It matters plenty if you start guessing the accuracy of the
enable required to achieve an accuracy (though you called it
resolution) of +/-1 event. Which you did.
 
J

John Fields

Jan 1, 1970
0
It matters plenty if you start guessing the accuracy of the
enable required to achieve an accuracy (though you called it
resolution) of +/-1 event. Which you did.

---
The assumption, asshole, for the porpoise of describing the initial
archietexture, was that the 65536 pluses were spaced equidistantly
in a window 1.0 pulse or minus something millie seconds wide.

Why are you getting your panties in such a bunch about what _might_
be happening in that window before the OP's even gotten back to us
with what he _really_ wants?
 
J

John Fields

Jan 1, 1970
0
k
Hmmmm ... maybe this calls for a flash ADC to estimate the number of
coincident photons and an adder instead of a counter.
 
Phil said:
** Got that right at least.

All the rests was just another load of fucking bollocks from a demented,
grossly autistic arrogant old fool.

Peeeukeeee.

Like I said, Phil's abuse is tediously repetitive - but he lives in
Sydney, and wouldn't know any better.
 
Fred said:
How did you make that leap into controlling the average rate at 2MHz?

20:1 slower than the peak rate was the rule of thumb amongst the
photochemists I've worked worked with.
Poisson time of arrival lamda=2E6 mean events per second makes for two
to occur at something like 0.5(lamda*25n)^2 or 0.125% ? Or two or more
to occur at 0.127%.

I'm sure you are right - I'll have to think about why ...
 
Since you were the one who didn't know how rotten a simple TTL one-shot
actually is, and had to be dragged through the calculations repeatedly
until the penny finally dropped, I think you had better give up that
second bottle of chardonnay until your brain gets back into contact
with reality.
But, I guess, there's always many a slip 'twixt the cup and the lip.
;)

Judging form your performance, you'd be better off with a few more
slips.
 
P

Phil Allison

Jan 1, 1970
0
Phil's abuse is tediously repetitive -


** But it ain't abuse - it is fact.

And the facts do not change.

YOU get to like it or lumpy it - you criminal fuckhead.




........ Phil
 
P

Paul Taylor

Jan 1, 1970
0
Like I said, Phil's abuse is tediously repetitive - but he lives in
Sydney, and wouldn't know any better.

Bill I think it is best if you ignore him and not get pulled into his
in-mature childish temper tantrums, that is probley what he wants any way
back to the job in hand. I have been having problems with my email so have
been unable to reply to any postings so far i have got a counter working
with a 1sec gate pulse ect... but when i go to 1msec this is where the
problems start?
 
R

rick H

Jan 1, 1970
0
If they were equidistant (only ever *your* assumption, not *the*
assumption), then where did your figure of 10ppm materialize from and
why would that figure need to be a "first-cut look"? Can't you take the
numbers 1e-3 and 65536 and divide them?
Why are you getting your panties in such a bunch about what _might_
be happening in that window before the OP's even gotten back to us
with what he _really_ wants?

No wedgies here, old chap. I simply pointed out that your assumptions
were flawed and hence your post was meaningless. You're the one getting
all steamed up.

I'll leave you to post the last insult, I suspect it's your style.
 
P

Phil Allison

Jan 1, 1970
0
"Paul Taylor = another criminal pile of pommy shit"
-----------------------------------------------------
Paul Taylor BSC (Hons)
Electronics Technician
School of Environmental Science
University of East Anglia
Norwich
NR4 7TJ



** **** OFF - you bloody impostor !!





......... Phil
 
P

Paul Taylor

Jan 1, 1970
0
John Fields said:
---
It is if you've got a low frequency and you've only got a short time
to measure it, but you've got different kind of problem if you want
to determine the frequency of a 1Hz signal in 1 millisecond.

Why don't you tell us _exactly_ what it is you're trying to
accomplish? That way we can probably help you decide on a good way
to go about getting it done instead of wasting a lot of time
guessing about what you want.

Type your reply _after_ the arrow. :)
John Fields
Professional Circuit Designer

Hi John sorry for the delay in replying the thread has sort of like split of
in all direction and i have been having problems with my news server, in a
nutshell

I have bought in a photometer which in turn is connected to a bought in
pulse amplifier discriminator (pad) this is from electron tubes part AD7,
this needs to be feed into a counter to count the pulses which I am to
build, the telemetry system is already in
place which I haven't built, the bottom line is I need to count the output
from the pad which counts the sodium particles and get this count back down
to earth.

I have a 1khz gate pulse for the count and 833khz (Clock signal) for sending
out the data via the telemetry system which is already in the rocket, i need
to count upto 2 power 16 or 65536 it is expected to loose the first bit so
32768 is an excepted maximum count.

Thanks
 
P

Paul Taylor

Jan 1, 1970
0
John Fields said:
---
Great idea! I was also thinking if the width of a single photon
event was specified, then smearing could be used to gate a fast
clock which would actually provide the edges for the counter's clock
as well as the 1ms window.

John you said about smearing could be used sorry but I don't understand what
this is? can you explain.
 
Paul said:
Bill I think it is best if you ignore him and not get pulled into his
in-mature childish temper tantrums, that is probley what he wants any way
back to the job in hand. I have been having problems with my email so have
been unable to reply to any postings so far i have got a counter working
with a 1sec gate pulse ect... but when i go to 1msec this is where the
problems start?

If the system works with a one second window, it ought to work with a
1millisecond window - logic doesn't usually start fallig over before
you get down to micorsecond time intervals.

As for rattling Phil Allison's cage - the longer we keep him mad, the
better the chance that he will blow a blood vessel and lose his
capacity to manipulate a keyboard. This would be a rather pyschopathic
motivation if one considered Phil to be fully human.
 
Y

YD

Jan 1, 1970
0
Hi John sorry for the delay in replying the thread has sort of like split of
in all direction and i have been having problems with my news server, in a
nutshell

I have bought in a photometer which in turn is connected to a bought in
pulse amplifier discriminator (pad) this is from electron tubes part AD7,
this needs to be feed into a counter to count the pulses which I am to
build, the telemetry system is already in
place which I haven't built, the bottom line is I need to count the output
from the pad which counts the sodium particles and get this count back down
to earth.

I have a 1khz gate pulse for the count and 833khz (Clock signal) for sending
out the data via the telemetry system which is already in the rocket, i need
to count upto 2 power 16 or 65536 it is expected to loose the first bit so
32768 is an excepted maximum count.

Thanks

In effect, what you're planning to do is open the gate for 1 ms, close
the gate, send the accumulated counts at 833 kHz by some modulation
scheme, reset the counter, open the gate, and so on. Sounds feasible.
If you want contiguous time slices things get a bit more complicated.
Let's see. After 1 ms shift out the data, reset counter, let
accumulate while the shifted data is transmitted. Sounds good if your
transmission scheme can handle it.

- YD.
 
P

Paul Taylor

Jan 1, 1970
0
YD said:
In effect, what you're planning to do is open the gate for 1 ms, close
the gate, send the accumulated counts at 833 kHz by some modulation
scheme, reset the counter, open the gate, and so on. Sounds feasible.
If you want contiguous time slices things get a bit more complicated.
Let's see. After 1 ms shift out the data, reset counter, let
accumulate while the shifted data is transmitted. Sounds good if your
transmission scheme can handle it.

- YD.
that is it in a nutshell, i can get it to run a 1sec gate but not 1msec?
 
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