Agilent Technologies 4294A Specifications download pdf (Page 9)

1-2. Measuring impedance

To find the impedance, we need to measure at least two values because impedance is a complex

quantity. Many modern impedance measuring instruments measure the real and the imaginary

parts of an impedance vector and then convert them into the desired parameters such as |Z|, θ, |Y|,

R, X, G, B. It is only necessary to connect the unknown component, circuit, or material to the

instrument. However, sometimes the instrument will display an unexpected result (too high or too

low). One possible cause of this problem is incorrect measurement technique, or the natural behav-

ior of the unknown device. In this section, we will focus on the traditional passive components and

discuss their natural behavior in the real-world as compared to their idealistic behavior.

1-3. Parasitics: There are no pure R, C or L

All circuit components are neither purely resistive nor purely reactive, they are a combination of

these impedance elements. The result is, all real-world devices have parasitics - unwanted induc-

tance in resistors, unwanted resistance in capacitors, unwanted capacitance in inductors, etc. Of

course, different materials and manufacturing technologies produce varying amounts of parasitics,

affecting both a component’s usefulness and the accuracy with which you can determine its resis-

tance, capacitance, or inductance. A real-world component contains many parasitics. With the

combination of a component’s primary element and parasitics, a component will be like a complex

circuit, if it is represented by electrical symbols as shown in Figure 1-5.

Figure 1-5. Component (capacitor) with parasitics represented by an electrical equivalent circuit

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Agilent Technologies 4294A Specifications Page 9