Learnto usean impedancemeasurer!The fundamental measurement techniques

Overview

Impedance metersare used to measure the impedancewhich is the resistance ofAC.(AC). Thisarticle provides anoutline of the fundamentals ofimpedance and methods of measuringimpedance, and howto utilize an impedance meter.

What isimpedance?

Let’s begin by definingimpedance. Inshort, impedanceisa measurement ofresistance to theflowthroughone’sAC current.

When you connect an electricproduct, motororany othergadget totheACsupply of power,current is able to flowthrough thecircuitry of the device. Impedance isdeterminedby dividing the voltage inthe circuit byits current. Inshort, impedance canbedescribed as restricting theflow of currentwithinanAC circuit. Impedance isindicated withan arrowsymbol “Z” and measured inOhms(O) (O), the samemeasurement unit that is used to determineDC resistance. Thegreater the impedance,thegreater resistance is thereto theflow of current.

How do you measure impedance?

As impedance itself isn’tan obvious phenomenon, it isimportant to have a measuringinstrumentto measureit. Instrumentsthat can measureimpedance include impedance meters,LCR meters, and impedance analyzer. There areseveralmethods in which impedance canbe measured.

Bridge method

Thismethod usesan abridge circuit to calculateanunidentifiedresistance. It requiresbalance adjustment tobecarried out using a galvanometer.While the method offersthe highest degree of accuracy(about 0.1%) but it’s not well-suitedfor high-speed measurements.

I-V method

This methodcalculates impedance through measuringthe voltagesacross the currentdetection resistor as well as an unknownimpedance. Itis also possiblefor measuringthe impedance of sampleswith a grounded.As the impedance increasesthetechnique becomes increasingly susceptibletothe effects ofthevoltmeter.

The RF I -V method

This method employsthe sameprinciple of measurementlike the I-V method. Itpermits high-frequency impedance measurementswith a circuit thatis compatible with the characteristic impedance ofthe high-frequency coaxial cable as well asan high-frequency coaxial connector.It’s challenging to employ thismethod to measure widebands becausethemeasurement frequency bandisrestrictedthrough the tests head’s transistor.

Automatically balancedbridge technique

This method employs the samefundamental measurement concept asthe bridge method. Itcoversan entire frequency range(11 mHz to 100 MHz).But, itdoesn’t extend to highfrequencies.A large number ofLCR metersuse this technique.

Each impedance analyzer method has its ownadvantages and disadvantages, soit is important to determinethe kind of impedanceyou need to measurebefore choosing the bestmethod to apply.

By using an impedance meter

The methodused to measure the impedancedepends on the instrument beingused.For example, Hioki’s LCMeter IM3523has the ability to measure impedancewith highaccuracy over a wide rangeoffrequency settings.

  • 40 Hz measurement

  • 200Hertz measurement

Alongside normal measurements the instrument is able tocontinuously and rapidly monitor variousparametersin variousconditions(measurement frequency andsignal strength).

  • C-D+ESR Measurement of Capacitors

impedance analyzeris also able to saveup to 60 setsof measurement conditionand up to128value of corrections for open/shortandcable length correction.It is possible to load groups of settingsimmediately loadedfor increasedefficiency.

In addition, the instrument’s externalcontrol terminalsallow you to buildautomatedtesting lines quicker.

The causes of instability in impedancemeasurement

The measurement methodthat is being used, impedance metersmay return a different valueeach time a measurement istaken. Ifthemeasurement results do not seem to be stable, check the following:

Particular components with parasitic properties of the component beingmeasured

Alongside the designvaluesfor resistivity and reactance,componentsalso have parasitic components thatcan cause a variance in measuredvalues.In addition, differences in thelength ofthe lead that is connectedtocomponents and thedistance between themcancause measured values to vary.

Measurementenvironment

The measurement of impedance results can beaffected by a wide range offactors, such asthe temperature of notonlyresistorsbut also inductors and capacitors as well asthe capacitance of probes and stray capacitance.

Thisrequirement requires actionsincluding maintaining a stablemeasuring environment and averaging of multiplemeasurements instead ofrelying on a singlemeasurement todeterminetheamount.

DC bias

DC biasis thesmallvoltage that occurs in measuringdevicesand circuits.For instance, it can occurwhen the wire and probearemade of different materials. Theresulting thermal electromotive forcecausesDC bias.

Summary

Impedance determines the degree of resistance toan AC current. Itsmeasurement requiresa specific instrument.Since there are a varietyofmethods for measuring, it’s important to choosethemost effective method, based onyour purpose and each method’sadvantages anddrawbacks.

The measurement of Impedance is verydelicate and is susceptible to variationsbecause of factors likefrequency, measurement environment as well asDC bias. Thischaracteristic requiresprocedures like averaging severalmeasurements.

Applications

  • Impedance measurement for Smart Keys/Immobilizers antennas

  • MLCC

  • Conductive polymer capacitors

  • Tantalum capacitors

How to Use

  • LCRMeasurement principles of the meter

  • How to Use an LCR Meter: Basic Knowledge