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hansibull
Is a dedicated frequency counter a must in a decent lab?
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on: November 12, , 07:50:59 pm »
Hi!
I'm slowly building up my own lab at home, and got already a hacked Rigol DSZ oscilloscope, and a few Fluke multimeters.
I'm able to get my hands on a Fluke/Philips PM frequency counter with the extra channel B (up to 1.3 GHz) installed. The price is about 150$ shipped. I already have a ~100 MHz frequency counter in my scope. Is a dedicated frequency counter something every EE with respect for him self should own? Is this a no-brainer, or is it even a useful tool when I have a digital oscilloscope?
The following users thanked this post: jonovid
nctnico
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #1 on: November 12, , 08:39:54 pm »
I think I use a dedicated frequency counter once ever 5 years or so. I have a HP but I have no idea if it even works if I need it. The frequencies showed on my oscilloscopes are good enough for 99.9% of my R&D work.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
retrolefty
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #2 on: November 12, , 10:24:01 pm »
Yea, I'm taking a minimalist route for a freq counter:
http://www.ebay.com/itm/?_trksid=p.m.l&ssPageName=STRK%3AMEBIDX%3AIT
karoru
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #3 on: November 12, , 10:31:33 pm »
Hi!
I'm slowly building up my own lab at home, and got already a hacked Rigol DSZ oscilloscope, and a few Fluke multimeters.
I'm able to get my hands on a Fluke/Philips PM frequency counter with the extra channel B (up to 1.3 GHz) installed. The price is about 150$ shipped. I already have a ~100 MHz frequency counter in my scope. Is a dedicated frequency counter something every EE with respect for him self should own? Is this a no-brainer, or is it even a useful tool when I have a digital oscilloscope?
Unless you need to tune a radio (i.e. transmitter for bands that requires you to transmit at particular channel, as for receiver a little misalign doesn't matter) you won't ever need one. If you want to rationalize spending some pocket money or a nice toy of course go for it, it's a nice piece of hardware to get yourself as a treat for birthday/christmas/whatever day you prefer to utilize for that, but nothing more:)
2N
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #4 on: November 12, , 10:46:02 pm »
I made a few products that needed precise timing, and to be calibrated to same frequency... So I bought a counter for that...
But you don't need it very often..
If and when you do you'll know..
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
David Hess
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #5 on: November 12, , 11:04:12 pm »
The Fluke/Philips PM is a pretty basic frequency counter but apparently so is the frequency counter built into the Rigol DSZ which I guess only reads out frequency to 6 digits. I would not bother with such a minor upgrade in capability unless I had a specific application in mind like measurements to 1.3 GHz.
My favorite not quite low end frequency counters are the old HP and HP which are universal reciprocal counters so they can do much more than the Fluke/Philips PM or Rigol DSZ. They can be had on Ebay for less than $100 but of course you run the risk of a non-working instrument.
G0HZU
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #6 on: November 12, , 11:18:39 pm »
I think the is a 9 digit reciprocal counter so in this sense it may have extra appeal for some applications. I've got an old 1.3GHz Philips counter here which is probably the same inside but has extra features on the front panel.
There are a few downsides with this counter model though.
The LCD display is very gloomy and difficult to read at certain angles unless you have favourable lighting on the counter, the standard timebase oscillator has a fairly poor spec for accuracy especially over temperature and the filtered rear mains power connector is one of the Schaffner types that is known to have exploding caps inside that cause the black plastic goo inside the connector to melt and spew out smoke.
$150 seems a lot for a model today. I paid £85 for my PM back in the early/mid s.
« Last Edit: November 12, , 11:22:49 pm by G0HZU »
David Hess
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #7 on: November 12, , 11:48:04 pm »
Ah, so it is a reciprocal counter which I guess produces 7 digits per second. That makes it nicer but I agree $150 is high considering what other used instruments are available for less.
lmester
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #8 on: November 13, , 01:11:48 am »
I have an HP A. It's on the far end of my equipment shelf. It's one of my lesser used instruments. I sometimes work with microcontroller circuits that deal with precise timing. I also have a GPSDO reference. If you need to accurately measure quartz crystal derived frequencies you'll need not just a counter but a good reference clock for it.
99% of the time I just use the counter built into my scope.
coppice
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #9 on: November 13, , 05:17:13 am »
Most labs don't have any frequency counters these days. If you work at customer sites, and need a counter for what you are doing, you'd better check in advance if they have one. If not, take your own.
tggzzz
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #10 on: November 13, , 07:59:12 am »
Rule of thumb: if you can't articulate why you need something, then you don't need it.
Without further information about what you would be measuring, if I had a choice between a frequency counter and a spectrum analyser, I'd choose the latter.
There are lies, damned lies, statistics - and ADC/DAC specs.
Glider pilot's aphorism: "there is no substitute for span". Retort: "There is a substitute: skill+imagination. But you can buy span".
Having fun doing more, with less
PA4TIM
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #11 on: November 13, , 09:10:39 am »
If you have to ask, you do not need one. Moderns DSO's also measure frequency related parameters.
I have a few VNA's and SA's, all klind of bridges, several calibrators and standards, a high resistance meter (up to peta-Ohm), 6,5 and 7,5 benchmeters, noise analyser, a slotted line etc, that does not mean every lab needs those too.
I have several counters and I use them, but not often. How often depends on the type of gear I get here for repair. I never had a HV diff probe but I often missed one so I bought one. And not just because every lab should have one.
Buy things you need.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl repair of test and calibration equipment
https://www.youtube.com/user/pa4tim my youtube channel
Ginettag20
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #12 on: November 13, , 08:06:18 pm »
I bought one to keep my bench DVM company.
Chris
hopski
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #13 on: November 13, , 08:20:14 pm »
Ha ha. Me too, they do get lonely.
David Hess
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #14 on: November 13, , 08:31:42 pm »
If you have to ask, you do not need one. Moderns DSO's also measure frequency related parameters.
They do but they are low performance compared to a dedicated frequency counter although I am not sure why this is. Maybe high end DSOs do better?
2N
Re: Is a dedicated frequency counter a must in a decent lab?
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Reply #15 on: November 13, , 08:53:07 pm »
If you have to ask, you do not need one. Moderns DSO's also measure frequency related parameters.
They do but they are low performance compared to a dedicated frequency counter although I am not sure why this is. Maybe high end DSOs do better?
Not really... no 10-12 digits resolution and base timebase accuracy and stability of a good counter..
But most scopes (even likes of Rigol) have counter that's good enough for generic work...
And cheap counters are not much better than those on scopes...
Cheapest counter I found that made sense was TTi 930/960.. It is basic 10digit counter, but good for what it is.. If you need better, you need to go name brands..
Also , surprisingly, Rigol DGZ AWG (and its Z brothers) has very decent counter channel, not fast, but it has basic analysis functions... Not bad for free....
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
Electronic measuring instrument
A frequency counter is an electronic instrument, or component of one, that is used for measuring frequency. Frequency counters usually measure the number of cycles of oscillation or pulses per second in a periodic electronic signal. Such an instrument is sometimes called a cymometer, particularly one of Chinese manufacture.[citation needed]
Operating principle
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Most frequency counters work by using a counter, which accumulates the number of events occurring within a specific period of time. After a preset period known as the gate time (1 second, for example), the value in the counter is transferred to a display, and the counter is reset to zero. If the event being measured repeats itself with sufficient stability and the frequency is considerably lower than that of the clock oscillator being used, the resolution of the measurement can be greatly improved by measuring the time required for an entire number of cycles, rather than counting the number of entire cycles observed for a pre-set duration (often referred to as the reciprocal technique). The internal oscillator, which provides the time signals, is called the timebase, and must be calibrated very accurately.
If the event to be counted is already in electronic form, simple interfacing with the instrument is all that is required. More complex signals may need some conditioning to make them suitable for counting. Most general-purpose frequency counters will include some form of amplifier, filtering, and shaping circuitry at the input. DSP technology, sensitivity control and hysteresis are other techniques to improve performance. Other types of periodic events that are not inherently electronic in nature will need to be converted using some form of transducer. For example, a mechanical event could be arranged to interrupt a light beam, and the counter made to count the resulting pulses.
Frequency counters designed for radio frequencies (RF) are also common and operate on the same principles as lower frequency counters. Often, they have more range before they overflow. For very high (microwave) frequencies, many designs use a high-speed prescaler to bring the signal frequency down to a point where normal digital circuitry can operate. The displays on such instruments consider this so they still display the correct value. Microwave frequency counters can currently measure frequencies up to almost 56 GHz. Above these frequencies, the signal to be measured is combined in a mixer with the signal from a local oscillator, producing a signal at the difference frequency, which is low enough to be measured directly.
If you want to learn more, please visit our website Portable Frequency Counter Factories.
Accuracy and resolution
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The accuracy of a frequency counter is strongly dependent on the stability of its timebase. A timebase is very delicate, like the hands of a watch, and can be changed by movement, interference, or even drift due to age, meaning it might not "tick" correctly. This can make a frequency reading, when referenced to the timebase, seem higher or lower than the actual value. Highly accurate circuits are used to generate timebases for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber, known as an oven-controlled crystal oscillator or crystal oven.
For higher accuracy measurements, an external frequency reference tied to a very high stability oscillator, such as a GPS disciplined rubidium oscillator, may be used. Where the frequency does not need to be known to such a high degree of accuracy, simpler oscillators can be used. It is also possible to measure frequency using the same techniques in software in an embedded system. A central processing unit (CPU), for example, can be arranged to measure its own frequency of operation, provided it has some reference timebase to compare with.
Accuracy is often limited by the available resolution of the measurement. The resolution of a single count is generally proportional to the timebase oscillator frequency and the gate time. Improved resolution can be obtained by several techniques such as oversampling/averaging.[1][2]
Additionally, accuracy can be significantly degraded by jitter on the signal being measured. It is possible to reduce this error by oversampling/averaging techniques.
I/O Interfaces
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Further information: Automatic test equipment
I/O interfaces allow the user to send information to the frequency counter and receive information from the frequency counter. Commonly used interfaces include RS-232, USB, GPIB and Ethernet. Besides sending measurement results, a counter can notify users when user-defined measurement limits are exceeded. Common to many counters are the SCPI commands used to control them. A new development is built-in LAN-based control via Ethernet complete with GUI's. This allows one computer to control one or several instruments and eliminates the need to write SCPI commands.
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See also
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References
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