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Measuring Frequency in a generator

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simonmeridew
Join Date: Oct 2005
Posts: 5 Northern Vermont
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2005-10-31          118725


How do you go about measuring frequency in a stand alone generator without a guage?
simonmeridew

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Measuring Frequency in a generator

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harvey
Join Date: Sep 2000
Posts: 1539 Moravia, NY
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2005-11-01          118734


I'm not an electrician. But there is no way to measure with out an instrument.

If you have a old plug in clock you can time the second hand and get in the ball park. This is based on what I've read can not tell you for sure it works. ....

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Measuring Frequency in a generator

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Chief
Join Date: Jul 2003
Posts: 4284 Southwest MiddleTennessee
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2005-11-01          118739


If you are asking how to obtain 60 hertz power output; the generator armature shaft must be turned at 3,600 rpm. Many small craft marine type generators as well as standby genrators are mated to engines which are governed at 3,600 rpm. Other manufacturers in order to reduce noise, vibration, and fuel consupmtion have gone to a 2:1 gearbox or pulley drive that spins the generator at 3,600 rpm. PTO generators are geared in a variety of drive ratio's but the bottom line is the generator must be spun at 3,600 rpm if you want 60 hertz power. ....

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Measuring Frequency in a generator

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metastable
Join Date: Apr 2004
Posts: 78 North Plains, OR
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2005-11-01          118759


Why not just buy a cheap meter? Something like:

http://store.yahoo.com/tmt/trip2030c.html

Unless your question was just one of curiosity, then frequency is simply 1/time. Equivalently, a Hertz = (1 cycle)/(1 second). You need 60 cycles/second, so if you know that your generator is based on a certain RPM, then you could potentially do things like strobe the drive shaft with a reference frequency or use magnetic pickups. But that is too much work...opt for the meter. ....

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Measuring Frequency in a generator

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AnnBrush
Join Date: Mar 2004
Posts: 462 Troy OH
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2005-11-03          118883


There is only one relyable way to do it, you need an oscilloscope. They can be easily found at the electrical engineering department of the local Uni or community college. Many Faculty will demonstrate the use of the device to their students if you are prepared to take the unit down to their location. We were always messing aroung with them in our Elec. Eng. labs at good ole UK (University of Kentucky) - Go Wildcats!! ....

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Measuring Frequency in a generator

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metastable
Join Date: Apr 2004
Posts: 78 North Plains, OR
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2005-11-04          118907


Huh? While it is true that you can view the signal on an oscilloscope, frequency measurement is far more accurate and safer with a ground-isolated (battery-operated portable) frequency counter. Connecting an oscilloscope to a generator or other A/C power source is dangerous since the case of the instrument is grounded to one of the leads. Hook it up wrong, and you'll risk electrocution and equipment damage.

But then, what do I know? I only have an MS in electrical engineering. :) ....

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Measuring Frequency in a generator

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AnnBrush
Join Date: Mar 2004
Posts: 462 Troy OH
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2005-11-04          118935


Metastable, you have to be kidding, what kind of oscilloscope have you been using. We used a "run of the mill" HP oscilloscope which was insulated to at least 1200 volts. It made no difference which lead was connected to which terminal since neutral (ground) was considered to be floating. There would not be a living elec. eng. student living if that was the norm. Oscilloscope manufacturers would have been sued out of existence? ....

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Measuring Frequency in a generator

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2005-11-04          118939


You can measure the frequency easily with a oscilloscope, but it is a bit of over kill. There are plenty of hand held meters available today. A meter or oscilloscope is only as good as it's timing chip. Some of the old oscilloscopes did not have that good of timing chips. Most are quartz today. ....

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Measuring Frequency in a generator

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simonmeridew
Join Date: Oct 2005
Posts: 5 Northern Vermont
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2005-11-05          118946


Thanks for all who are helping me.
So I can get a frequency meter at Radio Shack, and connect across the hot 115 lead and the neutral and read directly? I did have an old analog VOM meter years ago which had a frequency mode in one switch position, but that's long gone. Now I have a digital VOM setup, but it doesn't seem to have any frequency reading capability.
simonmeridew ....

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Measuring Frequency in a generator

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2005-11-05          118954


Not every meter is capable of reading the frequency. Mine doesnot either. The better meters are inductive, they just clip over the electrical wire. ....

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Measuring Frequency in a generator

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jdcman
Join Date: Jul 2003
Posts: 103 washington
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2005-11-06          118992


well the other inexpensive way to do the job, (provided you have some technical skills), is purchase a small acquisition card or microprocessor eval card, suck the data into your pc and take the fft.

obviously you'd have to glue on some pre-conditioning stuff to isolate the eval board, but you could do this all for less than 50 bucks and have some fun to boot.

then again it might be easier to just purchase a cheap dmm with this capability built in. ....

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Measuring Frequency in a generator

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-11-07          119045


"(provided you have some technical skills)"

jd, technical skills is the operative term here. Let's see, first you have to get the signal down to about 4 volts, then you have to convert from analog to digital. Store that time series. Figure out the bit order that your specific A-D converter puts out so you can make sense of the numbers. Write a fast Fourier transform program unless you have already spent the money on Matlab or some such program. Oh hell, this doesn't have to be fast, a simple discrete FT will work for this one time problem. Then by knowing the frequency of the digital sampling, figure out what frequency the FT'd peak represents.

Jd, I've got to hand it to you, your plan would work. And it would probably be fun. Sounds alot like my job though.
Dave ....

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Measuring Frequency in a generator

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
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2005-11-07          119056


Sounds about right shortmag. At least that is how we did it 23 years ago to an apple 1. Naturally the cost was about 5X the 50$ back then. ....

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Measuring Frequency in a generator

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-11-07          119057


Peters, maybe I'm living in the past too. I remember doing stuff like this on an intel 286.

Is there a $50 board that comes with the FFT and display software?
Dave ....

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Measuring Frequency in a generator

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metastable
Join Date: Apr 2004
Posts: 78 North Plains, OR
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2005-11-07          119072


I stand behind my comment about oscilloscope grounding and safety. Since there are many safety-concious individuals here, I've pasted a link and quote from a major manufacturer of oscilloscopes. Ann--There is no need to risk someone's life with bad advice because you got lucky.

Reference:
http://www.tek.com/Measurement/cgi-bin/framed.pl?Document=/Measurement/App_Notes/Technical_Briefs/tds3000-float/eng/limitations.html&FrameSet=oscilloscopes

Quote:
"Most oscilloscopes have their "signal common" terminal connected to the protective grounding system, commonly referred to as "earth" ground or just "ground." This is done so that all signals applied to or supplied from the oscilloscope have a common connection point. This is usually the oscilloscope chassis and is held at (or very near to) zero volts by virtue of the third-wire ground in the power cord for AC-powered equipment. It also means that, with few exceptions, all measurements must be made with respect to "earth" ground. This constrains the typical oscilloscope (at least in a single measurement) from being used to measure potential differences between two points where neither point is at earth ground."

....

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____________________________________________________________________________________
Measuring Frequency in a generator

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Peters
Join Date: Feb 2002
Posts: 3034 Northern AL
TractorPoint Premium Member -- 5 Tractors = Very Frequent Poster  View my Photos  Pics

2005-11-07          119074


Shortmag; I think in total with software and computer it was near 100X, but that was for fast accusition and predated the 8088 let alone the 286. I think the unit we had which was built out of boards with cassette programming and no display was 2X times this, although it was retired when we built the Apple. Sounds like old history now. ....

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Measuring Frequency in a generator

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jdcman
Join Date: Jul 2003
Posts: 103 washington
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2005-11-07          119114


hey dave,

i'm an rf eng by trade, but have recently been mucking around with the avr micro-p from atmel.

for about 60-70 bucks you can purchase an eval board that comes with a micro that has a 10 bit a-d with an 8 port mux, 3 counter-timers, pwm capability, uart and serial port communication and 32 config i/o's.

i'm actually evaluating the part for use as a controller in a pll application.

with a wall-wart, resistive divider, an rc low pass filter for anti-alias, pc and excel spread sheet --- one now has the capability of low freq spectral analysis of the generator.

matlab is my preferred post analysis tool, but if youíre handy with c code or visual basic youíre good to go.

i might be pointing out the obvious, but if one wants real time measurement of the period vs the spectral content the use of the real time counters combined with the built in analog comparator is the way to go.

and if one gets real ambitious consider using the micro in a control loop to set the speed of the motor, thus the freq output from the generator --- now weíre talking fun!

iím actually amazed at the power of these inexpensive parts ---- iím old enough to remember the days of the PDP-8ís and 11ís in college and getting a big smile when I printed out my name on the teletype!

have fun ---
....

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Measuring Frequency in a generator

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-11-08          119120


jdc, Its good to know that the tractor board has some expertice in radio frequency engineering.:) I teach a class in hands-on MRI and today we just happen to be building simple RF receive only coils for the scanner. They'll have to lay out the copper tape in a license plate sized rectangle, and tune them with the proper capacitors to 63.8 MHz. Then they build a blocking network so they don't burn up when they're subjected to the main RF pulses. About half of them have some soldering experience so the end results are sometimes ugly. They always work though, many times better than the factory coils with pretty covers.
Dave ....

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Measuring Frequency in a generator

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dsg
Join Date: Jun 1999
Posts: 528 Franklin, Maine
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2005-11-10          119179


O.K. you guys, enough with the I.Q. jousting:)) I'm not an engineer and know notthing about DMMs and have wanted one for some time now. So from the link of the earlier post for Time Motion Tools I found one that wasn't $300.00 or more. What is your opions? The first link is the one I bought because they did not have in stock my first choice (link #2). DM15XL Should I have waited for my first choice?

David


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Link:   DMM

 
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Measuring Frequency in a generator

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-11-10          119187


The one you bought should work well. It's also almost half the cost of the cheapest on the other page. I have two cheap analog meters that I use and they've always done everything I needed them for so this one would be a real cadillac for me. :) The real engineers here might have better feedback for you.
Dave ....

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Measuring Frequency in a generator

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metastable
Join Date: Apr 2004
Posts: 78 North Plains, OR
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2005-11-10          119189


That is a nice meter, but does it do frequency? ....

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Measuring Frequency in a generator

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dsg
Join Date: Jun 1999
Posts: 528 Franklin, Maine
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2005-11-10          119198


metastable, that I'm unsure of. I don't even know if my first choice could read frequency?

David ....

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Measuring Frequency in a generator

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shortmagnum
Join Date: Nov 2003
Posts: 848 Wisconsin
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2005-11-10          119201


Metastable, here's one for $69 that measures frequency. There may be cheaper ones.
Dave ....


Link:   multmeters

 
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Measuring Frequency in a generator

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jdcman
Join Date: Jul 2003
Posts: 103 washington
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2005-11-11          119229


dsg,

dmm's are tools ---

therefore, as with any tool, in order to determine if it's the correct tool for the job a description of the application is appropriate.

what do you want to do with the meter? what type of jobs do you have in mind?

as an example, i have an old analog meter,(vom), that would service 98% of the measurements that the ave guy is going to make around the shop or house.

this thing is capable of resistance measurements, voltage (dc and ac), and both ac and dc current measurements.

the newer instruments have digital readouts and are auto setting thus making them easier to use.

most of the measurements that a guy needs to make around the house revolve around continuity, voltage and current.

maybe you have stated elsewhere what your needs are and i've just missed it --- but coming up with the app is crucial in terms of making a good decision.

hope this helps.


....

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Measuring Frequency in a generator

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dsg
Join Date: Jun 1999
Posts: 528 Franklin, Maine
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2005-11-11          119238


jdcman, Thank you for your input. Yes just the average around the house stuff, power tools etc. I would like to test my generator but not a must.

David
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petrabrule
Join Date: Apr 2014
Posts: 2
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2014-04-25          190170


In modern times. there are various kinds of secure devices to provide safe environment for people. For example the security camera can be used to monitor suspicious person come and go in the office or people's own home. Besides the metal detector with the frequency of a microwave can also be used to set up a security system to ensure our safety in the daily life. ....

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