Every time I look this up I am being shown how to use a Multimeter. But I want to know WHAT exactly is that multimeter doing? It is looking at the potential difference? But what exactly are the components doing inside. What would the simplest Multimeter look like
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Simplest is a meter movement (coil, magnet and needle) with a resistor in series. The meter directly measures current (current in coil creates magnetic field which moves needle), but the resistor converts voltage to current.
Fancy meters have more to them and are thus able to perform better in various ways. But that’s the basic idea.
Analog meters measuring voltage will tap a tiny portion of the voltage through a resistor and put it across a meter movement- the meter moves the needle further when more voltage is applied.
Digital meters use a capacitor and measure how quickly that capacitor charges and discharges when the voltage is connected, along with an internal voltage reference.
Big secret of the world…. EVERY meter is an ammeter. That is, a meter that reads current, resistance, voltage, power (watts)…. all actually just calibrated in a way to read current, as current is truly measurable. For this example of a volt meter, two leads are connected across the thing you want to measure the voltage of, within those leads is a very large resistor. The trick is to have the resistor significantly higher resistance than everything else in the circuit, so that only an extremely small current travels through the meter, bit the resistance is a known value (say 10k ohms) then by utilizing meter deflection to read amps, a simple equation is used to garner the voltage. (Generally it is Voltage=current x resistance). I say current is the only truly measurable thing because voltage is simply a potential difference between one thing and another, to truly measure that you would have to pick one point, count up all the electrons at that point and calculate the charge, and pick the separate point and do the same, its much easier to connect a known circuit between them and measure how much current flows, because with current flow there is a measurable magnetic field developed which its strength is proportional to current flow. So I can make that field deflect a needle on a meter face, or with fancy digital meters measure the field and spit out actual numbers.
A digital multimeter will often use a delta sigma ADC. The way it ultimately detects voltage is with the electric field of electrons on the gate of a field effect transistor. Basically, the electric field increases in strength the higher the input voltage(more electrons in the same space), and the electrons on the gate repel the ones that are trying to get through the transistor.
The simplest multimeter is the electromechanical kind the others have covered.
Yes, analog meters exist and are fairly simple, but they are not really often used any more.
Analog oscilloscopes would amplify the voltage and use it to deflect electrons flying towards phosphors embedded on a screen.
Pretty much everything you’d use today is digital. This means that a circuit known as an analog to digital converter (ADC) is used to produce a digital value of a measured voltage. There are dozens of different ways in which they do this. Check out the [ADC page](https://en.wikipedia.org/wiki/Analog-to-digital_converter) of wikipedia to see several of them.
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