Design And Development Of Portable Digital LCR Meter By .
International Journal of Innovations in Engineering and Technology (IJIET)Design and Development of Portable DigitalLCR Meter by Auto Balancing Bridge MethodP. KanakaRajuDepartment of Electronics and Physics, GIS,GITAM University, Visakhapatnam, INDIAM. PurnaChandra RaoDepartment of System Design,Andhra University, Visakhapatnam, INDIAAbstract-This paper describes the development and evaluation of a custom-built LCR meter, which uses a multiplexedbridge circuit to characterize the properties of electronic components. The LCR meter is constructed on a single printedcircuit board with minimum components like: 8-bitMicrocontroller, TL08XX-Operational amplifier [1], CD405x-CMOSsingle 8-channel analog Multiplexer/Demultiplexer [2], OP07-ultra-low offset voltage operational amplifier [3] and issufficiently compact for integration into a handheld format. The instrument is designed to measure the inductance (L),capacitance (C), and resistance (R) of a component along with sub parameters- D, Q, θ, Effective Series Resistance atdifferent frequencies. The custom built LCR meter having the following specifications: basic accuracy- 0.3%-0.5%, autorange mode, auto calibration, test range – R (0.0002 Ω — 9.999 MΩ), L (0.01 μH — 1000 H) and C (0.1 pF — 10000uF).The designed instrument performance is compared with a standard a LCR meter, the percentage of error between themis less than 1.Key words: Auto balancing bridge, Microcontroller, 8-channel analog Multiplexer/Demultiplexer, Operational amplifierand PCB with minimum componentsI. INTRODUCTIONLCR meter is an electronic testing instrument used to measure the inductance (L), capacitance (C) andresistance (R) of a component. Inductance is the property of an electrical circuit causing voltage to be generatedproportional to the rate of change of current in a circuit. Capacitance is the ability of a body to hold an electricalcharge, it is a measure of the amount of electrical energy stored for a given electric potential. The electricalResistance is a measure of its opposition to the passage of an electric current. In general, these quantities are notmeasured directly, but determined from a measurement of impedance. Impedance is a parameter used to evaluate thecharacteristics of electronic components. Impedance (Z) is defined as the total opposition a component offers to theflow of an alternating current at a given frequency.II. IMPEDANCE PARAMETERSImpedance is represented as a complex, vector quantity. A polar coordinate system is used to map thevector as shown in figure 1, where quadrants one and two correspond to passive inductance and passive capacitancerespectively, quadrants three and four correspond to negative resistance. The impedance vector consists of a realpart, resistance (R), and an imaginary part, reactance (X). Capacitance (C) and inductance (L) are derived fromresistance (R) and reactance (X). The two forms of reactance are inductive (XL) and capacitive (XC). The QualityFactor (Q) and the Dissipation Factor (D) are also derived from resistance and reactance. These parameters serve asmeasures of reactance purity. When Q is larger or D is smaller, the quality is better. Q is defined as the ratio of theenergy stored in a component to the energy dissipated by the component. D is the inverse of Q. D is also equal to“tan δ”, where δ is the dielectric loss angle (δ is the complementary angle to θ - the phase angle). Both D and Q aredimensionless quantities. Figure 2 describes the relationship between impedance and the derived parameters.Volume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016130ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)Figure 1. Impedance VectorFigure 2. Capacitor and Inductor ParametersImpedance is measured using a variety of methods; Table 1 shows the comparison between major impedancemeasurement methods as well as the frequency ranges covered.MethodAutoBalancingBridgeI-VRF I-VNetworkanalysisAdvantageMost accurate,Wide impedancemeasurement rangeWide frequency coverageGroundeddevicemeasurementProbing measurementAccurateimpedancemeasurementthrough the GHz rangeGroundeddevicemeasurementVery broad frequencycoverage (LFthrough uency range5 Hz – 40 MHzLimited frequency andimpedance measurementrangeLimitedfrequencycoverage10 kHz–100 MHzImpedance measurementrange is limited tovalues close to thecharacteristic impedanceof the analyzer 10 kHz1 MHz – 1.8 GHzApplicationAllimpedancemeasurementapplications in tsandmaterialsmeasurement in RFComponentsmaterialsmeasurementandTable 1. Comparison of impedance measurement methodsIII. DESCRIPTION OF THE AUTO-BALANCING-BRIDGE LCR METERFigure 3 shows the circuit diagram of the Auto-Balancing-Bridge method [6]. To perform preciseimpedance measurements, the voltage applied to the device under test (DUT) and the current which flows throughthe DUT need to be accurately measured. The voltage applied to the DUT is detected as V1 at the High-Potential(Hp) terminal of the instrument. The terminal is isolated from the High-Current (Hc) terminal which is a signaloutput terminal. This isolation enables accurate detection of the voltage applied to the DUT. The current whichflows through the DUT, goes to the Low-Current (Lc) terminal. If there exist a certain potential at the Lc terminal,stray capacitance between the terminal and ground is generated and current may flow to ground. To avoid this, theLOW terminal is kept near the voltage level of ground. This is called a Virtual Ground and it is functionallydependent on a feedback loop. The feedback loop is called a null-loop. The null amplifier consists of an inputamplifier, a narrowband high-gain amplifier and an output amplifier. This circuit maintains the virtual ground at theLp terminal, and pulls the current to a range resistor. By detecting the voltage of the range resistors, the currentwhich flows through the DUT is measured. Impedance analyzers usually have several range resistors in order toachieve high-resolution for various current measurements. With the technology of this feedback loop, the cablingmethod called a Four-Terminal-Pair (4TP) [5] configuration is used. This configuration minimizes error factors thatexist in the measurement path as shown in Figure 4. The measurement path refers to the path from thevoltage/current measuring circuit in the instrument to the DUT connection. The 4TP configuration removesinfluences such as the series residual impedance of a cable, stray capacitance between cables and mutual inductanceVolume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016131ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)of cables. With this configuration, a wide range of impedance can be measured from low- Z to high- Z. Figure 5shows the circuit diagram of the latest Auto-Balancing-Bridge technology. The signal generated by a signal sourcewill flow in the circuit. This methodology can provide the most accurate measurements through the use of the AutoBalancing-Bridge method with the Four-Terminal-Pair configuration [8].Figure 3. Circuit diagram of the Auto-BalancingFigure 4. Four-Terminal-Pair configuration-Bridge methodFigure 5. Combination of the Auto-Balancing-Bridge with the Four-Terminal-Pair configurationIV. DESIGN AND FABRICATIONThe LCR meter is constructed on a single printed circuit board with minimum components like:STC12C5A60S2- eight-bit Microcontroller [4], TL08XX-Operational amplifier, CD405x-CMOS single 8-channelanalog Multiplexer/Demultiplexer, OP07-ultra-low offset voltage operational amplifier and is sufficiently compactfor integration into a handheld format as shown in figures 7a, 7b, 7c, and 7d. The instrument is designed to measurethe inductance (L), capacitance (C), and resistance (R) of a component along with sub parameters- D, Q, θ, ESR atdifferent frequencies. The custom built LCR meter having the following specifications: basic accuracy- 0.3%-0.5%,auto range mode, auto calibration, test range – R (0.0002 Ω — 9.999 MΩ), L (0.01 μH — 1000 H) and C (0.1 pF —10000uF).Volume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016132ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)Figure 7a. Circuit diagram of the LCR meterFigure 7b. Printer Circuit Board of LCR meterFigure 7c. Fabricated LCR meterFigure 7d. Front panel of fabricated LCR meterV. OPERATIONThe device under test (DUT) is subjected to an AC voltage source [6]. The meter measures the voltage across andthe current through the DUT. From the ratio of these the meter can determine the magnitude of the impedance. Thephase angle between the voltage and current is also measured. In combination with the impedance, the equivalentcapacitance or inductance, and resistance, of the DUT can be calculated and displayed. The meter assumes either aparallel or a series model for the elements. LR measurements have the elements in series and that CR measurementshave the elements in parallel. This handheld LCR meters typically have selectable test frequencies of 100 Hz, 1 KHzVolume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016133ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)and 7.8 kHz. The display resolution and measurement range capability will change with test frequency. The custombuilt LCR meter having the following specifications: basic accuracy- 0.5%-1%, auto range mode, auto calibration,test range – R (0.0002 Ω — 9.999 MΩ), L (0.01 µH — 1000 H) and C (0.1 pF — 10000uF).The measuring error in impedance measurement is a complex function of the measurand so that referenceimpedance valued in the whole measuring range is needed for the calibration. Thus self calibration system wasdeveloped in this design. The measuring errors are compensated by the signal processing using the self-calibrationmeasuring data. The measuring accuracy of the resulted measuring system depends only on the tolerance of thereference elements.Features of designed LCR meter: Display: LCD display shows measured values, entered parameters, instrument status, and user messages. Making Measurements: Measurements are performed at test frequencies of 100Hz, 1 kHz, and7.8 kHz, built-in drive voltage can be set to preset the voltage level.Measurements are taken at rates of 2, 10 or20 samples per second. Both series andparallel equivalent circuit models of a component are supported. Auto measurement: AUTO measurement mode automates the selection of setupparameters andquickly determines the appropriate device model for whatever componentis being measured. Calibration: Automatically corrects both open and short circuit parameters at allfrequencies andall ranges. Test Fixtures: This LCR meters have a Kelvin fixture which uses two wires to carry the test current andtwo independent wires to sense the voltage across the device under test. This prevents the voltage drop in thecurrent carrying wires fromaffecting the voltage measurement. Radial components are simply inserted intothe test fixture, one lead in each side. Axial devices require the use of the axial fixture adapters which will alsobe providedVI. RESULTS AND DISCUSSIONAfter the completion of the design and fabrication of the LCR meter, its performance was tested by makingvarious measurements on a group of components like resistors, inductors and capacitors. The measurands are with /- 10% tolerance. The values of the components shown by the LCR meter are compared with the printed values onthe components and tabulated in table 2a, 2b, and 2c. Figures 8a, 8b, 8c, 8d, 8e and 8f are some of the evidences forthe estimation of the designed LCR meter’s performance. The graphs 1, 2, and 3 shows that the measured values ofthe components are track the marked values on the components.S.N012345678910Resistor - R in ohmsMarked value with /- 10 % tolerance1050100110101010K50K100K500K1000KLCRMeter Displayin KHz1KHz1KHz1KHz1KHzTable 2a. Comparison of marked and measured values of Resistance with sub-parametersS.N012Inductor - L in HenryMarked value with /- 10 % tolerance10 micro H50 micro HVolume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016LCRMeter Displayin 46134ESRMeasuredFrequency1.4451.6611KHz1KHzISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)3456789101mH4 milli H10 milli H100 milli H500 milli H1H5H10 H1137 micro H4.109 milli H10.010 milli H103.55milli H502.0 milli H983.0 milli H4.954 H9.972 89.0189.1389.0689.212.8534.85.8823560.0921.98 Mohms3.6 M ohms1KHz1KHz1KHz1KHz1KHz1KHz1KHz1KHzTable 2b. Comparison of marked and measured values of Inductance with sub-parametersS.N0LCRMeter Displayin FaradsQDThetaESRMeasuredFrequency1Capacitor- C inFaradsMarked valuewith /- 10 %tolerance22 pico F19.9 pico F16.230.049-93.191KHz210 nano F10.826 nano F330.20.003-89.833456789100 nano F0.22 micro F0.47 micro F1 micro F4.7 micro F10 micro F22 micro F99.85 nano F209.7 nano F444.0 nano F937.3 nano F4.345 micro F9.838 micro F20.26 micro 80.18-80.97 20 Mohms5.01 Mohms7 ohms13.66.9 ohms7.9 ohms4.04 ohms2.87 ohms1.276 ohms1KHz1KHz1KHz1KHz1KHz1KHz1KHz1KHzTable 2c. Comparison of marked and measured values of Capacitance with sub-parametersFigure 8a. Measuring 100 Ω Resistor (colour code)Volume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016Figure 8b. Measuring 10 KΩ Resistor (colour code)135ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET)Figure 8c. Measuring 100 mH Inductor (box)Figure 8d. Measuring 10 mH Inductor (box)Figure 8e. Measuring 0.22µFarads CapacitorFigure 8f. Measuring 10 µFarads CapacitorFigure 8. Measurement of Resistors, Inductors and Capacitors by using the designed LCR meter1M100k100k10k10k1k1k1001001010112468Marked Inductance in HenryMarked Resistance in Ohms1M0Marked InductanceObtained 1E-50102468Obtained Inductance in Henry10MMarked resistanceObtained resistanceObtained Resistance in Ohms10M10Number of eventsNumber of eventsFigure 1. Marked resistance verses obtained resistance Figure 2. Marked inductance verses obtained inductanceVolume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016136ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
rked CapacitanceObtained Capacitance101010101002468Obtained Capacitance in Micro FaradMarked Capacitance In Micro FaradInternational Journal of Innovations in Engineering and Technology (IJIET)10Number of eventsFigure 3. Marked capacitance verses obtained capacitanceVII. CONCLUSIONThis paper describes the design and fabrication of low cost LCR meter, useful for research and educationalpurpose. It is very easy to operate, because automatic ranging system was incorporated and it also automaticallyselects the type of components we measure. It automatically switches between series and parallel connection of themeasured components. The front panel controls are user friendly. Experimental results shows that the designed LCRmeter is of high precision, small size, convenient and stable in use. The graphs 1, 2, and 3 shows that the measuredvalues of the components are track the marked values on the components, the error percentage is almost less than 1.However, further improvements are needed for the measurement of large valued R, L and C components andimprovement is required for high frequency t/stc/stc-ad-pdf/stc12c5a60s2-english.pdfYu. Kneller and L. P. Borovskikh, “Determination of the Parameters of Multielement Two-TerminalNetworks”,Énergoatomizdat, Moscow (1986)K. B. Karandeev and G. A. Shtamberger, “The eneral Teory of Alternating Currnt Bridge Ciruits”, Izd. SOAkad.NaukSSSR, Novosibirsk (1961).V. G. Plotnikov, “Quasi-Balanced Circuits for Measuring the Parameters of Objects Represented by MultielementElectricTwoTerminal Networks”, L’vov (1987)Mills, C.A., Chai, K.T.C., Milgrew, M.J., Glidle, A., Cooper, J.M., and Cumming, D.R.S. (2006), “Amultiplexedimpedance analyzer for characterizing polymer-coated QCM sensor arrays”, IEEESensors Journal, 6(4), pp. 996-1002Volume 7 Issue 3 October 2016Volume 6 Issue 4 April 2016137ISSN: 2319 - 1058Volume 6 Issue 4 April 2016
International Journal of Innovations in Engineering and Technology (IJIET) 130 Volume 6 Issue 4 April 2016 Volume 6 Issue 4 April 2016 Volume 7 Issue 3 October 2016 ISSN: 2319 - 1058
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