EMF Probe With Meter Circuit: What Type of Meter Is Used and How Does It Work?

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#31 21659896 13 Oct 2011 15:00

Mike Burr Mike Burr

Anonymous

Post #31
21659896 13 Oct 2011 15:00

Something you might look at, instead of the LF351, some single supply low power amplifiers. something similar to a LM386. It's a low power audio amplifier, single supply instead of the +/- that the 351 uses.

I'll have to try it this weekend to see how it works out.
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#32 21659897 13 Oct 2011 15:18

Luca Tarpini Luca Tarpini

Anonymous

Post #32
21659897 13 Oct 2011 15:18

My problem is that I'm a student with the hobby of electronics. I don't know the pratical tips to improve the circuit? I trust you, but because a single supply should be better?
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#33 21659898 13 Oct 2011 15:29

Mike Burr Mike Burr

Anonymous

Post #33
21659898 13 Oct 2011 15:29

the original circuit shows a 9V source. The 351 is an amplifier designed to work with a +15 and -15V source together. When working with a single source supply. Dual source amplifiers don't function as well as those designed to operate on a single supply.

Here is a good article to help clear up the difference.
http://www.unc.edu/~finley/Device Design/Are single- and dual-supply op amps interchangable.pdf
#34 21659899 13 Oct 2011 15:31

Mike Burr Mike Burr

Anonymous

Post #34
21659899 13 Oct 2011 15:31

Here is the pdf, because the link didn't display properly.
#35 21659900 17 Oct 2011 11:20

Luca Tarpini Luca Tarpini

Anonymous

Post #35
21659900 17 Oct 2011 11:20

Hi, Mike!
If you have tested the circuit let me know how it works, thanks!

I have a new question: in practical, how I connect the meter? Is it necessary some transduction o some transittion?
#36 21659901 17 Oct 2011 12:44

Mike Burr Mike Burr

Anonymous

Post #36
21659901 17 Oct 2011 12:44

Luca,

Here is a second version of the probe. I found the original shown on emanorama.net and found that a second version that was a little more stable was made. It has a little better gain control and isolates the meter and audio outputs.

http://www.epanorama.net/zen_schematics/Circuits/Testgear/emfprobe2.html

I'm building it this weekend, and will probably build the other if I can find enough amplifiers. I will most likely use my fluke to measure the current instead of using the FSD 250uA indicator.
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#37 21659902 18 Oct 2011 13:15

Luca Tarpini Luca Tarpini

Anonymous

Post #37
21659902 18 Oct 2011 13:15

Ok I see the second circuit but first i want try to build the first schematic.

A little question: I see in my simulation a current of amplitude about 500-600 uA. If the meter has FSD of 250uA it will be saturate from the current!Isn't it?
The current is too high respect the FSD of tne meter!
#38 21659903 19 Oct 2011 08:22

Mike Burr Mike Burr

Anonymous

Post #38
21659903 19 Oct 2011 08:22

If you are seeing the 500-600 uA at the meter points, it could cause it to deflect very hard. In physical operation it will be more difficult to be able to generate the 10mV with the coil. More likely you will be able to pick up uV instead of mV. It will be a process of trial and error to find the best fit for the coil.
#39 21659904 19 Oct 2011 12:07

Luca Tarpini Luca Tarpini

Anonymous

Post #39
21659904 19 Oct 2011 12:07

Last question: I see in the meter an alternate current. Is it correct? Could the meter work with this current?
Souldn't it be a direct current?
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#40 21659905 20 Oct 2011 09:23

Mike Burr Mike Burr

Anonymous

Post #40
21659905 20 Oct 2011 09:23

It should be coming through as a DC level, however with the diodes, it should prevent it from going negative. there will be an effective DC voltage component to the waveform and shouldn't cause the meter to wobble too much.
#41 21659906 01 Nov 2011 14:23

Luca Tarpini Luca Tarpini

Anonymous

Post #41
21659906 01 Nov 2011 14:23

Hi, Mike! How do you do? Do you build and test the circuit?
#42 21659907 01 Nov 2011 14:27

Mike Burr Mike Burr

Anonymous

Post #42
21659907 01 Nov 2011 14:27

It's currently half built. I ended up having to put it aside as system builds got in the way. I have the circuit laid out and wired, just adding in the resistors and caps to power.

I'm hoping I have some time this week to work with it, instead of troubleshooting systems.
#43 21659908 04 Nov 2011 05:51

Luca Tarpini Luca Tarpini

Anonymous

Post #43
21659908 04 Nov 2011 05:51

Hi!
I'm going to built the circuit. Onq question: what I need to connect the 9V to the circuit? Can you link me the components? Sholud I find 9V batteries?
#44 21659909 04 Nov 2011 06:51

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #44
21659909 04 Nov 2011 06:51

It looks like the transistor amp is not needed. The op amp can drive the meter.
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Topic summary

The discussion centers on understanding and simulating an EMF probe circuit with a meter, specifically clarifying the type of meter used and its operation. The meter is identified as a small DC panel ammeter with a full scale deflection (FSD) of 250 µA, measuring DC current resulting from rectified AC signals. The circuit uses diodes and a capacitor to rectify the AC signal induced by an electromagnetic field into a DC current suitable for the D'Arsonval analog meter movement. Simulation challenges include observing extremely low currents (picoamperes or femtoamperes) and negative oscillations in the meter current, attributed to simulation setup issues such as source modeling and measurement points. Proper simulation requires placing the inductor as the field coupling element, using a sinusoidal source at appropriate amplitude and frequency, and measuring current after the diode rectification stage. Frequency response shows the circuit performs well from 10 Hz to about 1-2 kHz, with roll-off and reduced meter current amplitude at higher frequencies like 10 kHz, which is expected due to circuit filtering effects. Practical considerations include using a 9 V power supply, selecting suitable op-amps (e.g., LF351 or alternatives like LM386 for single supply operation), and understanding that the meter current should be a DC level after rectification to avoid meter needle oscillation. A second, more stable version of the probe circuit with improved gain control and isolation is also referenced. The discussion emphasizes trial and error in coil design and component selection to optimize sensitivity and meter response.
Summary generated by the language model.