Sensing current through AC motor

[Boncuk]

Here is a cheaper solution for an instrumentation amplifier.

It uses input offset correction as well as amplifier offset correction. For high accuracy the circuit must have a symmetrical supply. The DC/DC converter delivers an insulated output voltage of -12V at 83mA. (Cost €4.70 incl. sales tax)

Using approximately 5Ω for RG the amplification factor is ~10,000. Formulas contained in the schematic.

R15 and D1 are added to prevent overvoltage on the A/D converter input.

In case the screenshot isn't clearly readable I attached a pdf file as well.

Boncuk

 

[Boncuk]

Math errors:

Replace R2/R3 with 1K5 (instead of 10K) for input zero adjust of ±1.24V and R12/R13 with 47Ω (instead of 120Ω) for offset adjust of ±11.9mV.

Boncuk

 

[premkumar9]

It's industry standard in Germany.

Unable to understand why 500Ω is fixed as the secondary load as a standard. Can you send some reading materials to know more about this?

 

[Boncuk]

Standard equipment in industrial applications works with analog input voltages, either 0-5V, 0-10V or 2-10V. Using a current loop of 0-20 or 4-20mA at a burden resistor of 500Ω the resulting voltage is 0-10 or 2-10V.

Current loops are only used for long distance signal transmission. Up to 1,000m the voltage drop across a 0.8mm diameter wire and a current of a few µA is negligable, and can be compensated by offset correction.

Anyway, for your application you don't require to convert current to voltage. The toroidal transformer delivers voltage, not current.

Current is a matter of the connected load (burden) and in that particular case you use voltage directly at a high impedance input.

I'm getting confused reading your replies. It seems to me you expect a solution conformal with your idea (which I guess is the wrong approach).

Boncuk

 

[premkumar9]

Anyway, for your application you don't require to convert current to voltage. The toroidal transformer delivers voltage, not current.

Do you mean that the toroidal transformer will give an O/P voltage proportional to the input current? If that is the case, can we get that voltage even when the secondary is left open?

I'm getting confused reading your replies. It seems to me you expect a solution conformal with your idea (which I guess is the wrong approach).

What can I do for that? I ask my doubts expecting that somebody with practical experience may give some useful suggestions.

 

[Boncuk]

You can't wait for a ready-to-use solution served on a silver platter.

Do some small scale experiments using any toroidal core with reasonably thick wire (e.g. as used in dimmers), put some windings of wire around the existing coil and use different known loads (e.g. sandwich toaster or water boiler) to connect to mains.

Then measure the output voltage at the secondary winding. If you deem it too low add some more windings.

The toroidal will behave like any transformer being connected with the load in series with the only difference, that the voltage drop across it is pretty low.

The photo I posted is part of practical experience and I explained it well.

 

[premkumar9]

I think what happens sometimes is that some people starts answering questions on which they don't have enough knowledge. It is OK.Nobody knows everything. But the problem is they don't show the humility to accept their mistakes and gets irritated when their replies are questioned. I am not intending any individual. Just mentioned one problem with many individuals.

 

[Boncuk]

That shoe won't fit me.

The toroidal as mentioned has been tested and is used in a functioning circuit.

On the other hand, if you want 100% proof and a scientific dissertation about the problem then why not ask a university professor?

 

[premkumar9]

That shoe won't fit me.

The toroidal as mentioned has been tested and is used in a functioning circuit.

On the other hand, if you want 100% proof and a scientific dissertation about the problem then why not ask a university professor?

I don't know who are all in this forum. There may be professors also. Normally I post questions for practical applications. Not for any school assignment. The toroidal transformer you made may be working fine for your application. My requirement is different. So I need to know the design aspects also to make one suitable for me. Doing it on trial and error basis may not be practical for me. I am thankful to you for all your suggestions. But my only suggestion not to get irritated when somebody questions your statements.

 

[Boncuk]

Normally I post questions for practical applications. Not for any school assignment.

Still unsatisfactory, because the answer doesn't include an exact describtion about the object to use.

The toroidal transformer you made may be working fine for your application. My requirement is different. So I need to know the design aspects also to make one suitable for me. Doing it on trial and error basis may not be practical for me.

With other words, you expect a ready-to-go design as well as you expect to do the trial and error work for you by others. (Served on a silver platter)

I am thankful to you for all your suggestions. But my only suggestion not to get irritated when somebody questions your statements.

There is absolutely nothing to question if a tested and working design has been described.

So get your butts up and do some research for your special requirements. The start is given.