# measure inductance without oscilloscope

Adjust the output voltage of the generator to 1 V peak-peak. This site uses Akismet to reduce spam. Read about it here. 3. R8 insures that static does not build up on the gate of Q1 and harm the transistor when the breadboard part of the circuit (outside the green box) is disconnected. How to remove Null plot markers in QuantilePlot? Asking for help, clarification, or responding to other answers. How did people measure capacitances and inductances before the invention of the oscilloscope? Does Windows know physical size of external monitor? Record the value of the calibrated capacitance ($C_1$). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. (Hantek 6022BE), Fix Internet Disconnect on phone pick up or hang up. Adjust the frequency of the generator to approximately 20 kHz. Pin 5 (C.2) on the PICAXE is a low-true signal to drive a pulse to the gate of Q1. Therefore, R10 is used as a dump load to absorb the excess energy. How can you measure capacitance/inductance without an oscilloscope? Switch works but outlet doesn’t. 4. site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. For that matter, with the lower value resistors, perhaps the gate was never fully turning off? This is similar to a TTL output, and should have a very low impedance both for charging and discharging the gate. It only takes a minute to sign up. Current builds up in the inductor according to the equation V = L di/dt. The current flowing through the inductor also flows through sense resistor R9. Attention!". Connect the unknown inductor parallel to the oscilloscope (Fig. Karen Orton (UK) improved the method proposed above for inductors which have a significant resistance. The measurement is carried out by substitution. Since most people will be more interested in the method rather than in the theory behind it, let’s start with a step-by-step description: 1. I have few ferrite core's (don't know the inductance coefficient) and I'm planning on building some simple cw transmitters-receivers. I need an inductor of a certain value for my solar bike. Since most people will be more interested in the method rather than in the theory behind it, lets start with a step-by-step description: The inductor, in combination with the internal series resistance in the generator form a voltage divider circuit (Fig. or "Attention! The initial pulse of current through R10 would be quite high, and result in a high voltage, except that C3 absorbs the bulk of the current spike. I have neither, so have to be creative about it. U3 is a bipolar part that has significant input bias current, so will charge C4 on its own if left alone. electromagnetism electric-circuits capacitance measurements inductance share | cite | improve this question | follow | Josephson junction: why do we need a capacitance in parallel to the inductance in the description? 2.1). The 5-volt output of the PICAXE may not be enough to turn on Q1 solidly, so Q2 and R6 are used to invert and level-shift the signal to 12 volts. Resonant methods for the measurement of electrical impedance were quite common in the past. This would be so much easier to debug if I could see what’s going on. Just for the heck of it, I decided to try driving the power MOSFET gate directly from a processor pin. R10 is actually a 12-volt automotive lamp, so that if Q1 is pulsed continuously, there should be a visual indication of the power output. You proceed as follows: Since you didn't change the source frequency and the inductance, the total capacitance is not changed between points 3 and 5. Here is pseudo-code for its program: And here is what it looks like in real life: [18-JUL-2013] I don’t fully understand the results I got. A once common instrument that allows resonant impedance measurements is the $Q$-meter. Is there a formula for absolute magnitude that does not contain an apparent magnitude term? Can I close my money in HSA and transfer it to another bank account and use it for non-medical purpose? Connect the 50 ohm output of the function generator to the oscilloscope, and select a sine-wave signal. A dual procedure, with series insertion, can be used for inductance measurements. Can I hover my finger over a chess piece without touching it in a major chess tournament? Without R7, there will be a big spark when the leads are initially connected, or when the switch is first turned on. Output from the program is sent through this same port to a terminal. The nice thing about a website is that people from time to time make very useful contributions. Then I dropped R1 to 137 ohms, and got 21.4 amps – close enough, given all the unknown tolerances in the circuit. Connect the 50 ohm output of the function generator to the oscilloscope, and select a sine-wave signal. So what happened? The power MOSFET had gotten so hot, it unsoldered itself, and as the wire sprung away, there was a blue spark. Well, at least that confirmed that high currents were present. It would be easy to measure an inductor with an LCR meter, or with a simple circuit plus an oscilloscope. Perhaps you, the reader, can help. I had low expectations. Unfortunately, working with scavenged and surplus parts, it’s hard to get the value I really want. I think I’ll have to break down and buy an inexpensive USB oscilloscope. Does the phase difference between voltage and current in an LCR circuit exist throughout the circuit? [23-AUG-2013] Update: I bought an oscilloscope, which made finding root cause of this issue easy. I have neither, so have to be creative about it. The current through the inductor is a function of both the frequency as well as the inductance. Anyone?? Adjust $C_v$ until the voltmeter reads the maximum value (resonance). To learn more, see our tips on writing great answers. Doi… (Kind of reminds me of high school, when I had only a multimeter, so measured capacitance by building an oscillator and listening to the tone through headphones…). So I changed R1 to 261 ohms, and got 19.4 amps. An example of $Q$-meter: Boonton Q-Meter Type 160-A. So it looked like I needed to do some work on the gate drive. Compile libpng as a Static Library for Windows with…, I Dropped an Oscilloscope on My Foot! Connect the unknown capacitor $C_x$ to the instrument in parallel to the variable capacitance (parallel insertion). Thanks for contributing an answer to Physics Stack Exchange! Use MathJax to format equations. Note that the supply voltage is only 5 volts here, but this seems to be all right, as the power MOSFET is designed for a logic level drive, with a low threshold voltage. Then, POP! Otherwise the procedure is exactly as described above. Also, this configuration uses less power than the RTL drive above, since the NPN transistor does not need to sink any static current for the low state. By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. There are several power supplies, but the 24-volt supply comes from lead-acid batteries. Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. When the PICAXE is going through initialization or programming, and its pins will float. You may also prefer L=4570/f with L in uH and f in kHz. If my calculations were correct, at that point, the lamp in the dummy load should have been at full brightness. Lx is the unknown inductor to be measured. Adjust the frequency of the generator to approximately 20 kHz. MathJax reference. With L in Henry and f in Hz. Perhaps there was not enough time to charge the MOSFET gate to turn on in the 10 uS pulse I was using? 3.1). I put in 137 ohms, expecting the result to be smaller, but then saw 25.8 amps. Measuring Inductance at High Currents without an Oscillosope. I connected a voltmeter across the dummy load, but was disappointed to see just 0.1 volt there when the duty cycle was cranked up to about 33%. Is "beyond your comprehension" an offensive phrase? This would be so much easier to debug if I could see what’s going on. I had not heat-sinked the transistor, thinking that these first few experiments would be at low power. What is the lowest first stage thrust for a launch reaching orbit? Simply DC measure the resistance first and use it in the formula below. With the inductor connected, the current through the inductor will cause a voltage drop over the 50 ohm resistor causing the amplitude of the signal on the screen of the scope to drop. This voltage is large enough to be measured, but small enough so as not to significantly interfere with the current through the inductor. [1] E. Rubiola, Laboratorio di misure elettroniche, CLUT, Torino, 1993. U3, D2, and C4 form a peak detector circuit that monitors the voltage across R9. Since we know what the current/voltage output of a RLC circuit is as a function of $R,L,C$ hooking up an $RLC$ circuit is one way to determine an unknown capacitance or inductance? I don't have oscilloscope but all other cheap tools I have and arduino, so if there is a way to make precise inductors like from 100nH to 2.2uH and 15uH. A $Q$-meter is an instrument capable of measuring the quality factor $Q$ of a resonant circuit. That processor has built-in A/D converters and pulse generators. Replaced an outlet and a switch. Announcement!" Adjust $C_v$ until you attain resonance again. If I actually end up using a totem pole, I will probably use NMOS and PMOS FETs, which will have less of this problem. When current is flowing through Lx, and Q1 turns off at the end of a pulse, voltage builds across Lx, possibly to levels that would destroy Q1 if left unchecked. Finally, read out the frequency, and calculate the inductance from L=4.57/f. Furthermore, from the $Q$ readings, you can obtain the capacitor's loss.