How to use inductance meter and precautions

The basic principle of inductance meter measurement is the constant current source method. Since the operational amplifier and peripheral components form an AC constant current source of a certain frequency, and then the voltage across the inductor connected in series in this constant current source circuit is measured, the inductive reactance of the inductor is obtained, that is, the inductance of the inductor is indirectly measured.

Calibration of inductance meter

After zeroing the inductance meter, insert a standard inductor into the inductor socket, for example, connect a 18μh inductor to the 20pμh block, adjust the resistor r5 so that it displays l8μh, and then calibrate the other blocks in the same way. Since the 20μh blocking current is large, about 4ma, which has reached the op amp output limit, this resistor is smaller than other blocking resistors. The remaining 4 resistors are basically related to 10 times. The other blocks can be deduced in the same way.

Things to note when measuring inductance with DC resistance and parasitic inductance meters:

Since the inductor has DC resistance and parasitic capacitance, this inductance meter measures the total impedance. Therefore, when the parasitic capacitance and DC resistance of the inductor are too large. The measurement error will also be larger. In order to reduce the influence of parasitic capacitance, when the inductance is large, the parasitic capacitance is often large and can only be measured at low frequency. to reduce errors caused by capacitance. For DC resistance, if the resistance is less than 10% of the inductive reactance at the measurement frequency, the measurement error is <0.5%; if the resistance is less than 20% of the inductive reactance, the error is <2%: When the resistance is greater than 20% of the inductive reactance, The error is too large. It is not suitable to measure, or the error caused by the resistance is eliminated after measurement.

Things to note when using an inductance meter to measure inductance with a magnetic core:

When using an inductance meter to measure an inductor with a magnetic core, the influence of the magnetic core's permeability must also be considered. Core permeability is not a constant, but a function of flux density. When the magnetic flux density is zero, the core has an initial permeability. When the magnetic flux density increases, the magnetic permeability increases, has a maximum value, and then decreases as the magnetic flux density increases. When the magnetic core reaches magnetic saturation, the magnetic permeability approaches l. When measuring the same inductor with a magnetic core, the readings in each gear are often different, and some errors can reach tens of percent or even several times. This is not an error in the inductance meter. But the working current of each block is different, so the magnetic core flux density is different, resulting in different magnetic permeability. This results in different inductances.