Monday, December 27, 2010
Weak current College】 【inductance measurements need to consider several basic questions】.
<br> <br> Switching power supply and communication industry's latest development inductors offers high-frequency characteristics and low loss, in the light of this requirement, the inductor testing process also turned to the higher areas. <br> <br> Describes an .inductor has several parameters, the most common measurement parameter is the value of inductance (L) and the quality factor (Q), DC resistance (DCR) is also a very useful parameters. <br> <br> Inductor is a wound of conductor ., is stored in the magnetic field energy devices (in contrast, the capacitor is in electric energy stored in the device). Inductors are a core and a group around the core of the windings. Because the air can be seen as a constant, therefore .it is the most simple core material, but from a practical efficiency, magnetic materials such as metal iron and ferrite is more common. Inductor in core materials, core length and winding turns, has a direct impact on the current-carrying capacity of an inductor .. <br> <br> Serial and parallel modes are available for measurement of inductance value: for large inductance value, given the relative frequency of reactor, so large a number of parallel impedance more prominent than the serial resistance and, therefore, should be .used in parallel equivalent circuit to test a large inductance. <br> <br> In contrast, low inductance values, reactor, which are smaller than concatenate impedance more obvious parallel impedance, which connects the equivalent circuit is a better way of measuring. For .very small inductor value, the higher the frequency, the better the accuracy. <br> <br> The actual measurement of inductance value <br> <br> The size of the inductance value is any one of the basic electrical characteristics of the coil ., it depends on the coil winding turns, the diameter of the coil, the length of the coil and the core features. <br> <br> By definition, inductance value is entire flux chain (Basic) and through the inductor or coil current .(I) ratio. Flux chain size depends on the medium (core material) magnetic permeability (μ) in size, that is the size of the inductance value and magnetic permeability is proportional. <br> <br> Magnetic permeability is describe certain material .magnetic field characteristics of a measurement parameters, it reflects the material can be magnetic penetration level on ferrite media, it is not a constant, with materials of composition and the magnetic flux density and change: <br> <br> Material itself does not change ., but the flux density is according to flow through the coil current. <br> <br> Quality factor <br> <br> Quality factor is the ratio of reactance and impedance, therefore it is a dimensionless parameter, which is a measure of .an inductor has more "pure" or "true" parameter (that is, it reflects how much an inductor has a ratio of pure reactor). <br> <br> Inductor Q the higher the value, it's a smaller loss. Dissipation factor .(D) is defined as 1 / Q, it reflects the total loss of components. Coil of copper material loss suffered D, Eddy current loss and hysteresis loss of common effects. <br> <br> Use DC bias <br> <br .> In order to accurately measure the size of the inductance value, the inductor must be tested under realistic conditions, ie in current flowing through the coil. LCR measurement instrument standards used AC source current is relatively small, and not suitable for measuring the power of .the sort used in high-current inductors. <br> <br> The actual measurement of inductance and does not require when using AC current source, you only need to use a DC and AC composite sources. DC bias can result in a deviation from .the inductor to normal working condition of the test conditions, so ordinary LCR measurement instrument can measure inductance. <br> <br> DC resistance measurement <br> <br> Measuring coil winding of DC resistance (DCR) or winding resistance values to determine .the appropriateness of wire diameter, the size of the winding tension, as well as in the production process of the connection. Winding reactance of size and current proportional to the frequency of change, that is why to measure DC resistance instead of AC impedance. In .the low-frequency, the DC resistance of wire is equivalent to the loss of copper wire, know how much of the core loss can be a more accurate estimate of the measured component D value. <br> <br> Voltage change <br> .<br> Due to the increase in the inductor voltage varies with the impedance and inductance by impedance and with the current changes. While the General LCR measurement instrument designed to measure the capacitive and resistive components, when used in the measurement of inductors, may cause .the inductance value. This error is due to the increase in the inductor voltage could not remain constant. Voltage level circuit can be used to monitor changes of inductive voltage on, go to the continuously adjustable programmable voltage source. <br> <br> Constant .power <br> <br> If a current flows through the inductor cannot remain constant, so the measured inductor inductance values will change, change the value of size is usually open programmable LCR Meter test voltage function. <br> <br> LCR measurement .instrument programmable voltage is in open-circuit condition, when measuring instrument internal resistance (RS) and AC output concatenate, through internal resistance will decrease after the voltage. When the tested components connected to the measuring instrument, the increase in the measured voltage component depends .on the size of the RS and the measured size of impedance. The internal resistance of the measuring instrument is normally 5 Ω ~ 100 k Ω. <br> <br> Loss General information <br> <br> Copper conductor loss in low frequency .conditions equivalent to the DC resistance of wire, and the current change of frequency is inversely with DCR measurement of inductance Analyzer can measure copper conductor loss. <br> <br> Iron and copper conductor of the Eddy current losses due to current flow through the .copper conductor into the heat of, it is proportional to the frequency. <br> Hysteresis loss of size and hysteresis surrounded by proportional to the size of the area, and the loop is the number of cross cutting (frequency) is proportional. It with .the signal amplitude changes (and not directly relevant), increases the frequency. But with the signal amplitude of numerical relationship is not very significant, given a signal level and cannot directly be detrimentalConsumption in size. <br> <br> <br>.