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How do you make a analog ac line voltage monitor 120 volt (RMS) scale? Answered

I would like to build a analog 120 volt RMS ac power line voltage monitor. That plugs into the wall to monitor my AC line voltage. Using a analog meter for display. How does one go about constructing such a device?  

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Rich_SBest Answer (author)2016-11-22

Here is a complete circuit, using a modified Wheatstone Bridge. The zener diodes are used to "start" the meter reading at 90 VAC input. The resistor values were chosen to give a mid-scale reading with 115 VAC input, using a 1mA DC panel meter that has 100-ohm internal resistance. If your panel meter is different, then you'll have to change R1 and R3 values.

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steveastrouk (author)2012-05-30

First find your meter......

Classically a "moving iron" meter is used, because they can measure AC directly. These days, you'll be OK with a bridge rectifier and a more common moving coil meter.

Once you have your meter, and you know what its impedance is, you calculate a suitable series resistor.

Here are some moving iron meters

http://www.eltime.co.uk/product.php/1/Moving%20Iron%20Meters.html

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sdnsg2 (author)steveastrouk2016-12-22

Sorry it has taken me so long to get back to you. How ever the US Navy had first call on my body. I live in the USA and I'm looking for something modern. And a nice big meter would be nice. Something like the size of the old Simpson 260 series VOM.

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sdnsg2 (author)steveastrouk2012-06-01

Could you draw me a schematic? Does the meter manufacturer provide you with a data sheet listing the impedance of its meter? If not how does one go about finding that information? And thank you steveastroukfor the help.

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steveastrouk (author)sdnsg22012-06-01
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sdnsg2 (author)steveastrouk2012-06-02

Thank you very much! I'll start looking for a meter come Monday. What would the ratting on the bridge rectifer need to be? Would 1/2 amp be OK?

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steveastrouk (author)sdnsg22012-06-02

The scale on the front bears very little relationship to the actual meter mechanism at the back.

Let me know where you are in the world,. and I can make some recommendations.

Are you looking for some kind of steam-punk retro vision, or something modern and utilitarian ?

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steveastrouk (author)sdnsg22012-06-01

If you get a moving iron meter, you can buy it off the shelf for a 110V supply or whatever.

If you are buying a moving coil meter, just take a look at the spec - or send me a link - before you buy it, and I'll tell you what to use.


steve

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iceng (author)steveastrouk2012-05-30

+1
Bloke sdnsg may be interested to know that analog meters were / are small electric motor rotors with a spring that attempts to return the pointer movement back to zero.

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sdnsg2 (author)iceng2012-06-01

Thanks for that info iceng. I had no idea that they were a small electric motor rotor.

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iceng (author)sdnsg22012-06-01
Makes sense when you think of it..........

Way back when Tesla was sparking for a living with GE
Somebody noticed the torque on a motor increased with voltage.

It's only easy to see the design process. 
  • Taking a small motor add a pointer
  • Fix a spring to the shaft
  • Prevent a full rotation
  • Discover brushes are not needed
  • Simplify the armature ( rotor )
  • Use permanent magnets for the field
  • Sell a useful analog product  :)
A

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Rich_S (author)2016-11-22

Here is a complete circuit. It uses a modified Wheatstone Bridge. The resistors R1 and R3 will have to be adjusted to suit your panel meter. The values shown are for a 1mA DC 100-ohm meter.

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