Author Topic: oscilloscope and frequency counter  (Read 14111 times)

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Oracle

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oscilloscope and frequency counter
« on: June 27, 2013, 09:41:44 pm »
Hi,

an oscilloscope, basically can display you a signal and measure it's own frequency. What is the difference between an oscilloscope and a frequency counter?? They do the same job: both of it can measure the frequency, and in any case an oscilloscope provide more information than a frequency counter do because you can see the waveform of a signal right?
 

Offline digsys

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Re: oscilloscope and frequency counter
« Reply #1 on: June 27, 2013, 09:53:51 pm »
An oscilloscope can do a HECK of a LOT MORE than just calculating a frequency !! For any reasonable oscilloscope, frequency isn't even
1% of what you can use it for. There are MANY cases where you don't even really give a rats arse what the frequency is, IF you're even able to
find one(?) in your signal !!! These are 2 ENTIRELY different tools. Your best bet is to google "how to" etc and read up on some of the applications.
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Online xrunner

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Re: oscilloscope and frequency counter
« Reply #2 on: June 27, 2013, 11:47:19 pm »
Perhaps he's asking why a separate frequency counter is needed when an oscilloscope can do the same job plus a lot more.  :-//
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Offline dfmischler

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Re: oscilloscope and frequency counter
« Reply #3 on: June 28, 2013, 12:35:14 am »
Perhaps he's asking why a separate frequency counter is needed when an oscilloscope can do the same job plus a lot more.  :-//

And the answer would be that a many-GHz frequency counter is really cheap compared to an oscilloscope that will show that waveform.  There are also some "universal" counter applications where the counter tells you exactly what you want to know and leaves the scope free for looking at something else.
 

Offline vk6zgo

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Re: oscilloscope and frequency counter
« Reply #4 on: June 28, 2013, 01:25:53 am »
An Oscilloscope is not as accurate as a standalone frequency meter,and its resolution is not as good.
A 'scope frequency display may be 1.99MHz,whereas a frequency counter may read 1.98776 MHz or something similar.

 

Oracle

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Re: oscilloscope and frequency counter
« Reply #5 on: June 28, 2013, 04:05:41 am »
So, it's only a matter of accuracy. Basically both of them can do the same thing, right?
 

Offline madshaman

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oscilloscope and frequency counter
« Reply #6 on: June 28, 2013, 04:17:37 am »
No, an oscilloscope shows a voltage waveform with respect to time.

A frequency counter counts events (usually filtered by a schmitt trigger).

Both *can* tell you the frequency of a signal.

Recently I used one of my oscilloscopes to verify my frequency counter and a signal generator at the same time.  When the counter and scope agrees, I knew the problem was the generator.

Having two pieces of test equipment that can give you the same value in different ways can often help solve chicken-and-egg problems.  For example, what if I didn't know if any of the three was working correctly?
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Offline WBB

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Re: oscilloscope and frequency counter
« Reply #7 on: June 28, 2013, 04:21:32 am »
Just use your scope as a frequency counter until you need an actual counter. When you do have that need, you'll know it.
 

Offline madshaman

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oscilloscope and frequency counter
« Reply #8 on: June 28, 2013, 04:32:58 am »
I think it should be a given that you don't buy test equipment if you don't know what you'll use it for; especially of you don't know what it does.

I suggest just read the wilipedia entry on both pieces of equipment.

I agree with this though, I'm constantly a noob in one area or the other, but the need for a piece of gear always arises from the process, doesn't go the other way around.
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Offline ejeffrey

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Re: oscilloscope and frequency counter
« Reply #9 on: June 28, 2013, 05:00:45 am »
One major difference is that a frequency counter measures the average frequency during some interval.  This is useful if you have random events like clicks from a Geiger counter.  Accuracy is obviously a big difference as well.  A typical ratio counter can measure ~9 digits / second for signals from Hz up to several hundred MHz, and is limited by the time base accuracy.  Frequency counters often have TCXO or OCXO oscillators, and many have Rb source options for extreme accuracy.  Measuring the period on a scope display will give you ~1% resolution.  On the other hand, a scope shows the actual waveform, which can avoid problems with bad signals.  If your signal is too small the frequency counter may trigger on noise, or if your signal has multiple zero-crossings per period, the counter will count them all.

 

Offline dr.diesel

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Re: oscilloscope and frequency counter
« Reply #10 on: June 28, 2013, 05:05:10 am »
I think it should be a given that you don't buy test equipment if you don't know what you'll use it for; especially of you don't know what it does.

That statement does against everything I believe in.  Test equipment is like boobs, you can never have enough and you can always just tweak the knobs till you figure out what you need it for.

Offline Lightages

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Re: oscilloscope and frequency counter
« Reply #11 on: June 28, 2013, 05:21:39 am »
Just use your scope as a frequency counter until you need an actual counter. When you do have that need, you'll know it.

 :-+
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Offline madshaman

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oscilloscope and frequency counter
« Reply #12 on: June 28, 2013, 05:23:30 am »
I think it should be a given that you don't buy test equipment if you don't know what you'll use it for; especially of you don't know what it does.

That statement does against everything I believe in.  Test equipment is like boobs, you can never have enough and you can always just tweak the knobs till you figure out what you need it for.

So, for example, by tweaking knobs on a vna setup, you're likely to figure out what to do with it?  Or even how to hook up the dut?  ;-)
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Offline dr.diesel

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Re: oscilloscope and frequency counter
« Reply #13 on: June 28, 2013, 05:27:35 am »
Yeah, might take a while though, but with some imagination you can't go wrong :D

Offline MasterOfNone

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Re: oscilloscope and frequency counter
« Reply #14 on: June 28, 2013, 05:38:30 am »
As mentioned above some Counters only measure frequency, while some which are usually called Universal Counters can offer more features which you may or may not need.
For instance if you were designing a system that uses pulses from something like an photo-interrupter, an oscilloscope would easily tell you the frequency of the pulses and this could be used to determine speed. While a Universal Counter could tell you the number of pulses which could be used to determine position, (but of course if the pulse count is low can manually count pulses on the oscilloscope).
Universal counters can also have features like the ability to divide the counts on two of its inputs and display the result.  So if you design a system that performs some function each time a pulse occurs, you could use a Universal Counter to verify that your system isn’t missing pulses by changing your system so that it outputs a pulse each time it thinks it has receives one. And then when you use the Universal Counter to divide the input to your system by the output from your system, the counter should always display near enough ‘one’, since any number divided by itself is one, (but the counter may need to be set so that it does large enough counts before performing the divide and displaying the result).
 

Offline os40la

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Re: oscilloscope and frequency counter
« Reply #15 on: June 28, 2013, 05:42:17 am »
So, for example, by tweaking knobs on a vna setup, you're likely to figure out what to do with it?  Or even how to hook up the dut?  ;-)
[/quote]

Sort of like an infinite number of rednecks, driving an infinite number of pickup trucks, fire an infinite number of shotgun rounds at an infinite number of highway signs will eventually produce all the world's great literary works, in Braille.  ;D
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Oracle

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Re: oscilloscope and frequency counter
« Reply #16 on: June 28, 2013, 06:21:54 am »
Just use your scope as a frequency counter until you need an actual counter. When you do have that need, you'll know it.

 :-+

yes. as soon as i don't need it i will use my scope, for sure!
 

Oracle

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Re: oscilloscope and frequency counter
« Reply #17 on: June 28, 2013, 06:27:10 am »
As mentioned above some Counters only measure frequency, while some which are usually called Universal Counters can offer more features which you may or may not need.
For instance if you were designing a system that uses pulses from something like an photo-interrupter, an oscilloscope would easily tell you the frequency of the pulses and this could be used to determine speed. While a Universal Counter could tell you the number of pulses which could be used to determine position, (but of course if the pulse count is low can manually count pulses on the oscilloscope).
Universal counters can also have features like the ability to divide the counts on two of its inputs and display the result.  So if you design a system that performs some function each time a pulse occurs, you could use a Universal Counter to verify that your system isn’t missing pulses by changing your system so that it outputs a pulse each time it thinks it has receives one. And then when you use the Universal Counter to divide the input to your system by the output from your system, the counter should always display near enough ‘one’, since any number divided by itself is one, (but the counter may need to be set so that it does large enough counts before performing the divide and displaying the result).
This seems intresting.... I also searched and founded that some counter can also display the signal phase between two channel...
 

Offline MasterOfNone

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Re: oscilloscope and frequency counter
« Reply #18 on: June 28, 2013, 07:31:44 am »
This seems intresting.... I also searched and founded that some counter can also display the signal phase between two channel...
To be fair if you hunt around it your scope measurement menu you’ll probably find that it can measure the phase between two waveforms, so it’s probably not a reason way you might need a counter.
 

Offline madshaman

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Re: oscilloscope and frequency counter
« Reply #19 on: June 28, 2013, 08:19:01 am »
Quote
So, for example, by tweaking knobs on a vna setup, you're likely to figure out what to do with it?  Or even how to hook up the dut?  ;-)

Sort of like an infinite number of rednecks, driving an infinite number of pickup trucks, fire an infinite number of shotgun rounds at an infinite number of highway signs will eventually produce all the world's great literary works, in Braille.  ;D

Lol, good laugh to end the day on :)
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Offline jaycee

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Re: oscilloscope and frequency counter
« Reply #20 on: June 28, 2013, 08:34:13 am »
Everyone here is also assuming the scope is a *digital* scope... my Tek 2213A can show me a waveform but thats all... i'd have to work out the frequency by hand, assuming it's even possible. You can make or buy a counter cheap enough that would tell you the frequency very accurately compared to trying to measure it on an analogue scope.
 

Offline vk6zgo

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Re: oscilloscope and frequency counter
« Reply #21 on: June 28, 2013, 11:36:04 am »
Everyone here is also assuming the scope is a *digital* scope... my Tek 2213A can show me a waveform but thats all... i'd have to work out the frequency by hand, assuming it's even possible. You can make or buy a counter cheap enough that would tell you the frequency very accurately compared to trying to measure it on an analogue scope.

It's quite possible----just measure the period of the waveform on the graticule,grab your calculator & work out the inverse of the period.
Or do it in your head!

It won't be highly accurate,but will get you "in the paddock".

What you can do with some analogue 'scopes is to connect the "Vert amp out" on the back to your frequency counter input so you have a counter with a high impedance input variable gain buffer amp which you can use to measure frequencies at those nasty little non-50 Ohm test points that manufacturers love to provide, ;D
 

Offline AlfBaz

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Re: oscilloscope and frequency counter
« Reply #22 on: June 28, 2013, 11:54:43 am »
and lets not forget you can use a counter to just count discrete events
 

Offline madshaman

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oscilloscope and frequency counter
« Reply #23 on: June 28, 2013, 04:19:22 pm »
Everyone here is also assuming the scope is a *digital* scope... my Tek 2213A can show me a waveform but thats all... i'd have to work out the frequency by hand, assuming it's even possible. You can make or buy a counter cheap enough that would tell you the frequency very accurately compared to trying to measure it on an analogue scope.

Not entirely true, my Tek 2465 is analog, but it has cursors and yeah, digital stuff for display generation.

It's still "manual"-ish, but I just plop some cursors across a cycle and it shows me the frequency.

Nothing near as accurate as my microwave frequency counter, but still useful, and fairly accurate.
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Offline madshaman

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oscilloscope and frequency counter
« Reply #24 on: June 28, 2013, 04:20:46 pm »
Everyone here is also assuming the scope is a *digital* scope... my Tek 2213A can show me a waveform but thats all... i'd have to work out the frequency by hand, assuming it's even possible. You can make or buy a counter cheap enough that would tell you the frequency very accurately compared to trying to measure it on an analogue scope.

It's quite possible----just measure the period of the waveform on the graticule,grab your calculator & work out the inverse of the period.
Or do it in your head!

It won't be highly accurate,but will get you "in the paddock".

What you can do with some analogue 'scopes is to connect the "Vert amp out" on the back to your frequency counter input so you have a counter with a high impedance input variable gain buffer amp which you can use to measure frequencies at those nasty little non-50 Ohm test points that manufacturers love to provide, ;D

Clever idea using a scope as a buffer ;-),
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Oracle

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Re: oscilloscope and frequency counter
« Reply #25 on: June 28, 2013, 09:09:02 pm »
This seems intresting.... I also searched and founded that some counter can also display the signal phase between two channel...
To be fair if you hunt around it your scope measurement menu you’ll probably find that it can measure the phase between two waveforms, so it’s probably not a reason way you might need a counter.

My scope don't have an option to measure the phase between signal, but it have a graticule, so possibly i can measure the phase between two waveform... but anyway i'm just wondering what application a frequency counter have, but as i see i'ts pretty limited of use: it's probably better have a good scope instead a counter, or a integrated counter on the oscilloscope. don't worth spend more than $1000 for that piece of equipment.
 

Offline jpb

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Re: oscilloscope and frequency counter
« Reply #26 on: June 28, 2013, 10:12:11 pm »
If you haven't looked at it already, you may like to look at this thread:

http://www.eevblog.com/forum/testgear/frequency-counter-do-you-really-need-one/

Counters generally cost a fraction of the price of an oscilloscope (say 10% to 20%). A $1000 counter is expensive so would be one that could measure frequencies well into the GHz and have psec time resolution perhaps. Most counters that you might want to get would be in the range $70 to $300 new and less on e-bay.

The choice is not scope or counter but scope alone or scope and counter.

Most modern digital scopes have a hardware counter built-in but this will be 5 or 6 digits, only do frequency not counting or period and so on and will only be as accurate as the scope timebase which is probably 25ppm. Adding a separate counter will give you more digits, other functions and much greater accuracy (especially if you can use an external reference frequency source) but none of this is really needed unless you do RF. Personally I got one because I wanted to do things such as adjust my 10MHz source to be 10MHz to 10 rather than 6 digits - more for the fun of it than for any dire need.
 

Offline rolycat

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Re: oscilloscope and frequency counter
« Reply #27 on: June 28, 2013, 10:52:42 pm »
Even if your scope doesn't have a hardware frequency counter, other test gear may do the job for you.

Many multimeters have a basic frequency setting up to a few hundred KHz, and some function generators also have external frequency measurement. For example, the Rigol DG1022 can measure frequencies up to 200 MHz. It has a 10 MHz reference input and can also calculate period, pulse width and duty cycle.
 


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