Analog frequency meter

Discussion in 'Power Electronics' started by colum, Oct 23, 2020.

1. colum

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Jul 25, 2013
I want to hook up an old analog needle type Hz meter but the needle swings wildly even with a stable Hz source...any ideas why and how to fix..Thanks....colum

2. Nanren888

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Nov 8, 2015
Image? model? schematic? source of meter?

3. davennModerator

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Sep 5, 2009

You need much more than just a meter to determine frequency

How about googling " circuits for analog frequency meters" and see what you find

4. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
The meter you have may be marked in Hz, but that doesn't mean it directly measures frequency (e.g. consider a meter with a scale of litres/minute - you wouldn't pour water into it)

An analog frequency meter is often driven by a circuit that converts a frequency to a voltage. One way of doing this is to convert the incoming signal into a pulse train of the same frequency, but with fixed length pulses. The average voltage of this equates to the frequency.

5. colum

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Jul 25, 2013
This meter is very old certainly before transistor and it does read the Hz with the reading roughly in the centered of the vibrating needle. I was just wondering what type of circuit would calm it down.
Could this kind of meter not work on sine waves or an amplitude issue.

6. Nanren888

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Nov 8, 2015
When you say "meter", do you mean a simple meter display or something that has active components, transistors or values?
.
What people were saying above is that there is no simple way to read frequency with just a moving needle meter without something active to count cycles, or to average pulses or similar.
One way is to generate a fixed length pulse per cycle of the input and then to average thw DC level. Again, needs active components.
This is the reason I asked for an image or description.
.
If you have just the moving needle display part, then it will read current, or maybe voltage; you'll need some circuitry attached that turns frequency into current of voltage.
Got a picture?

7. colum

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Jul 25, 2013
Thanks Nanren888. I see what you mean about the input conditioning. As a hobby during the pandemic I 'm fixing old old power supplies and the input for the " tuned coil " vibration meters need amplification adjustments to read correctly but are Ok with sine waves.. the needle meters are much tougher apparently...Jeff

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9. colum

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Jul 25, 2013
Hi bertus. Sorry my camera is busted..I have round faces that are either 60 cy + - and 400 cy + -
and a load of vibration meters that are placed on motors that record the rotations of many speeds and one that is hand held that shows 1750 rpm + - all with no electric contact..I've spent too much time at flea mkts....Jeff

10. bertusModerator

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Nov 8, 2019
Hello,

Could it be that there is a frequency to voltage converter needed for the meter?
The LM2907 / LM2917 chips are capable of converting the frequency to a voltage.

Bertus

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11. davennModerator

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Sep 5, 2009
You dont have a phone camera ?

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12. hevans1944Hop - AC8NS

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Jun 21, 2012
@colum: Jeff, does your location of Midhudson mean Mid-Hudson, this area of New York State? Is your avatar a photo from a model railroad, HO gauge perhaps? Just curious.

BTW, I like the old resonant vane frequency meters, but modern electronics makes it pretty easy to get a wider frequency range and better accuracy... unless your interest is just in the antiques.

Back in the day (1950s and 1960s) electronic tachometers driven from the breaker points in the ignition system were all the rage in hobby magazines. I always drove vehicles with automatic transmissions (until I began driving motorcycles), so I never needed a tachometer. Nevertheless, my first "real" car was a 1968 Mercury Cougar with an automatic transmission and... you guessed it... a tachometer. Go figure. This car also had "way cool" sequential rear turn signals. Unfortunately the implementation was electro-mechanical (motor-driven switches actuated with cams), so eventually it failed and the cost to replace it was prohibitive.

13. WHONOES

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May 20, 2017
hevans1944 likes this.
14. colum

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Jul 25, 2013
Thanks Hevans 1044 for your interesting history. I live in sight of the old RR bridge in Poughkeepsie NY and was in use up to the 1970s but caught fire and was abandoned until 2005 or so then it has became a very long walkway over the Hudson river
from Pok to Highland. I don't know much about trains but Im really fascinated by them. I did travel from London to Hollyhead England in a steam train a long time ago
My interest in these meters are trying to resurrect old power supplies in particular the tuned coil that can register the speed of the rotor by just contact with the housing ( try that electronics ) and they are accurate too but probably only AC motors
Be well...Jeff

15. hevans1944Hop - AC8NS

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Jun 21, 2012
Pretty spiffy IC you linked to, @WHONOES, although the spec sheet does say the frequency-to-voltage conversion (in which the OP is interested) takes longer than the voltage-to-frequency conversions, but the accuracy is impressive either way. Something "new-to-me" I should learn to play with.

@colum: I am not familiar with "the tuned coil" method of rpm measurement. Is it based on some sort of mechanical resonance, perhaps measuring minute vibrations given off by a slightly unbalanced rotor of the motor whose speed you want to measure? If that is true, then the "rpm meters" should work with AC as well as DC motors, since the vibrations are solely a mechanical phenomenon. OTOH, motor manufacturing has been pretty much a done deal since the beginning of the twentieth century, with a lot a attention paid to bearing design and reduction of rotating losses. That's why you can buy drone aircraft electric motors with speeds upwards of ten thousand rpm today. And I can remember when air-powered, water-cooled, turbines used in dental drills became all the rage, eventually completely replacing belt-and-pulley electric-motor-driven dental drills.

16. colum

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Jul 25, 2013
Hi hevans1944. If you are still interested I have started my old Sony H1 camera and will send some photos of the Tuned coil meters but I'm not sure about file size on these forums or if there is a way to send the photos directly there are about 12. ..colum

17. bertusModerator

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Nov 8, 2019
Hello,

When you resize the pictures to have a size of about 300 kB, you will be fine.
You can add the pictures to a post using the "Upload a File" button.

Bertus

18. colum

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Jul 25, 2013
Got it, you may get one or two at a time so that you can see finer details. Some are very old

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Jul 25, 2013

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