how to measure a capacitor or an inductor with mp3 player - energy storage devices

This is a simple technology that can accurately measure the capacitance and inductance of the capacitor and inductor without expensive equipment.
The measurement technology is based on a flat bridge and can be easily constructed with cheap resistors.
This measurement technology can not only measure the capacitance value, but also measure the effective series resistance of the capacitor at the same time.
Required components: 1.
Few variable resistors. A MP3 player3. A multimeter4.
A calculator to calculate the value. As an introduction to the project, let's take a look at what an LCRS Bridge is and what it takes to make an LCRS Bridge.
If you just want to create an lcr Bridge, skip these steps.
In order to understand the work of the lcr bridge, it is necessary to discuss the behavior of capacitors, resistors and inductor in the AC circuit.
It's time to clean up your ECE101 textbook.
Resistance is the easiest element to understand.
When the DC current passes through the resistor, the behavior of the perfect resistor is the same as when the AC current passes through the resistor.
It provides resistance to current flow, although it consumes energy by doing so.
The simple relationship between current, voltage and resistance is: R = I/VA perfect capacitor is a pure energy storage device on the other hand.
It will not disperse any energy through it.
Conversely, when the AC voltage is applied to the capacitor terminal, the current through the capacitor is the current from which the capacitor is added and removed.
Therefore, the current flowing through the capacitor is not phase compared to the end voltage of the capacitor.
In fact, it is always 90 degrees ahead of the voltage at both ends of the terminal.
The simple way to represent this is to use imaginary numbers (j):V (-j)(1 / C)
Similar to capacitors, the inductor is a pure energy storage device.
As an exact addition to the capacitor, the inductor uses a magnetic field to maintain the current flowing through the inductor and adjust its end voltage when doing so.
Therefore, the current flowing through the inductor is 90 degrees ahead of the terminal voltage.
The equation representing the relationship between voltage and current at both ends is: V (j)(L)
= IAs a summary, we can draw the resistance current (Ir)
Inductor current (Ii)
And capacitor current (Ic)
All on the same vector map, as shown in the figure.
In a perfect world with perfect capacitors and inductor, you can get a pure energy storage device.
However, nothing is perfect in the real world.
A key quality of the energy storage device, which may be a capacitor, battery or pump energy storage device, is the efficiency of the energy storage device.
There will always be some energy loss in the process.
In a capacitor or inductor, this is the acid resistance of the device.
In a capacitor, it is called a loss factor, and in an inductor it is called a mass factor.
A quick way to model this loss is to increase the series resistance in a series of perfect capacitors or inductor.
Therefore, the capacitors in real life look more like a perfect resistor and a perfect series capacitor.
A bridge has four resistance elements in total.
There is also a signal source and meter in the center of the bridge.
The element we control is the resistor element.
The main function of the resistance Bridge is to match the resistance in the bridge.
When the bridge is balanced, it means that the resistor R11 matches the R12, The R21 matches the R22, and the output on the center meter is zero.
This is because the current flowing out through R11 and the current flowing out of r2 through R21.
The voltage between the left side of the meter and the right side of the meter will then be the same.
The beauty of the bridge lies in the source impedance of the signal source, and the linearity of the meter does not affect the measurement.
Even if you have a cheap meter, it requires a lot of current for measurement (
For example, an old-fashioned analog instrument)
, As long as it is sensitive enough to tell you when there is no current flowing through the meter, it still does a good job here.
If the signal source has a large output impedance, the current drops through the output voltage caused by the bridge on the left side of the bridge with the same effect as the right side of the bridge.
The final result cancels it itself, and the bridge can still match the resistance with significant accuracy.
Careful readers may notice that the bridge will also be balanced if R11 equals R21 and R12 equals r2.
We do not consider this situation here, so we will not discuss it further.
In this example, the bridge will be balanced once the Z11 matches the z12.
To keep the design simple, the right side of the bridge consists of resistors.
A new requirement is that the source must be an AC power source.
The meter in use must also be able to detect AC current.
The Z11 and Z12 can be all three impedance sources, capacitors, inductors, resistors or combinations. Good so far.
If you have a bag of perfectly calibrated capacitors and inductor, then the bridge can be used to find out the value of the unknown device.
However, it will be very time consuming and expensive.
A better solution than this is to find a way to simulate a perfect reference device with some tips.
This is where the MP3 player enters the picture.
Remember that the current flowing through the capacitor is always 90 degrees ahead of the terminal voltage?
Now, if we can fix the end voltage of the device under test, it is possible for us to apply a 90 degree current in advance and simulate the effect of the capacitor.
To do this, we must first create an audio file containing two sine waves with a 90 degree difference between the two.
Upload this waveform file to the MP3 player, or play it directly from the PC, and the left and right channels produce two sine waves of the same magnitude.
From this point on, I will take the capacitor as an example for the sake of simplicity.
However, the same principle applies to the inductor in addition to the fact that the excitation signal needs to lag 90 degrees.
Let's first redraw the bridge of the device under test with a perfect capacitor in series with a perfect resistor.
When referring to another signal, the signal source is also split into two signals, one of which is offset 90 degrees in phase.
Now, here is the terrible part.
We must study the mathematics that describes the work of this circuit in depth.
First, let's look at the voltage on the right side of the meter.
In order to make the design simple, it is better to choose the right side of the resistor equal, so Rm = Rm, the voltage at the Vmr is half of the Vref.
Next, when the bridge is balanced, the voltage on the left and right side of the meter will be exactly equal and the phase will match perfectly.
Therefore, Vml is also half of the Vref.
With this we can write: Vml = Vref/2 = Vcc VrcLet and now we try to write through R90 and r2: Ir0 = (Vref / 2)x (1 / Ro)Ir90 = (Vz -(Vref / 2))/ (R90)
In addition, the current flowing through the device under test is: Ic = Ir0 ir90 now, assuming that the device under test is a capacitor, we want Vz to lead the Vref 90 degrees, and the calculation is simple. we can standardize the voltage of Vz and Vref to 1 v.
Then we can say: Vz = j, Vref = 1Ir0 = Vref /(2 x Ro)
= Ro/2Ir90 = (j -0. 5)/ (R90)
Together: Ic = Vml /(-j Xc + Rc)-j Xc + Rc = (0. 5 / Ic)
Where Xc is the impedance of the perfect capacitor Cc.
Therefore, by balancing the bridge and finding out the values of r2 and R90, it is possible to simply calculate the total current of the device passing the Ic under test.
Using the final equation we get, we can calculate the impedance of the perfect capacitor and the series resistance.
By understanding the capacitor impedance and the frequency of the applied signal, it is easy to pass through: Xc = 1 /(2 x π F C)1.
Play wave files using a PC or MP3 player. 2.
Connect the output of the MP3 player according to the wiring diagram shown above, if you are measuring the inductor, please exchange the connection to the left and right channels. 3.
Connect the multimeter and set the measurement on the AC voltage. 4.
Play the audio clip and adjust the trim pan until the voltage reading is minimized.
The closer it is to zero, the more accurate the measurement will be. 5.
Disconnect the equipment under test (DUT)
And MP3 players. 6.
Move the multimeter lead to R90 and set the measurement to resistance.
Measured values. 7.
Do the same for R0. 8.
Calculate the capacitor/inductor value manually or solve the value using the provided Octave/Matlab script.
Thank you for reading this manual.