Measuring inductance? - Page 1
Forum section: electronics / general

author: conducteur
author_rank: Regular Contributor
timestamp: August 19, 2019, 02:57:23 pm
content: I wonder why (i can't find one that does) multimeters can measure a variety of things like voltage and current, resistance, diode check, temperature, capacitance, frequency, .... but if you want to measure inductance you have to buy an LCR meter. Is there a specific explanation for this? Why can't they include an inductance mode on a multimeter?

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 19, 2019, 04:03:35 pm
content: Just guessing, but measuring inductance isn't that popular as a pastime. People that do need to do it probably want to measure small values, so a high measurement frequency is needed.

author: bob91343
author_rank: Super Contributor
timestamp: August 19, 2019, 04:28:07 pm
content: The cute little Chinese Mega328 'magic box' measures inductance.It's certainly true that most inductances are specific to particular frequency ranges. So you need to know ahead of time whether it's a power supply choke or a 50 MHz tuning element. Many inductances utilize iron in some form for a core to increase inductance and that causes nonlinearity both with frequency and signal amplitude.So while it's not that tough to set up a measurement, the result may or may not be useful.As an example, put an inductance of fairly large value on an LCR bridge and switch between parallel and series measurement, and then do the same at a different frequency. You will be very confused by the results.So you need to know how the component will be used to make a meaningful measurement.

author: Henrik_V
author_rank: Regular Contributor
timestamp: August 19, 2019, 05:50:30 pm
content: Inductivities are the most complex () Elements of the passiv ones. Cs are usually cheaper and smaller ...RC filters are cheaper & smallerso why bother with frequency depending µ_r ,expensive copper etc..Changed with higher frequencies ...

author: MosherIV
author_rank: Super Contributor
timestamp: August 19, 2019, 07:02:57 pm
content: As Henrik_v says, it is difficult.Most multimeters are based around voltage and time measurement. All the functions are some form of voltage or time based.There is no way to measure inductance just with dc voltage or time.The typical way to measure inductance is to measure the impedance (ac resistance) and it is usually done at different frequencies eg 100Hz, 1KHz and 10KHzThis technique can also be used to measure capacitanceDmm measure capacitance by measuring the capacitor charge up time.Another interresting way to measure inductance and capacitance is to put them into an oscilator circuit where the L or C affects the resonant frequency and then the freq can be measured to determine the L or C value.There is an interresting PIC 16C54 based lcr meter that uses this idea.

author: Andreas
author_rank: Super Contributor
timestamp: August 19, 2019, 07:32:01 pm
content: Hello,I am currently trying to measure some inductances with my scope.I am measuring the Ratio of voltages before and after the inductor from a sine generator with frequency sweep.After the inductor I have a 50 Ohms terminator on the 2nd input of the scope after the inductor.As you can clearly see: the inductor behaves only up to 2 MHz as a inductor.From the 50 Ohms and the division ratio you can calculate the inductance. (but at which frequency).with best regardsAndreas

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: August 20, 2019, 12:07:25 am
content: Quote from: conducteur on August 19, 2019, 02:57:23 pmThey do. One example:https://www.amazon.com/Digital-Multimeter-Inductance-Frequency-Capacitance/dp/B0140WS2NK