15.1 Introduction

A power meter may be used to measure the electrical power that a source is capable of delivering to a specified load impedance, or it can be used to measure the electrical power that a source furnishes to an arbitrary load impedance. Many factors influence the selection of a power measurement technique; these include frequency range, power level, the spectral content of the signal, and the required accuracy. No single instrument satisfies all these requirements, and a wide variety of power meters and measurement techniques are available which satisfy the specific objectives of a given set of measurement requirements.

15.2 Basic Power Definitions

Power is defined to be the rate at which energy is transferred between systems or elements within a system. A given element may either supply energy (power is furnished by the element which is acting as a source) or energy may be absorbed by the element (power is delivered to an element which acts as a load). Two broad categories of power measurements emerge from this discussion:

1. Meters or measurement techniques which determine the power transmitted through the meter or measurement system from the source to the load (transmission measurements)

2. Meters or measurement techniques which absorb the measured power (absorption measurements)

The basic definition of power is described by the following relations:

(15.1)

Monitoring the rate of change of energy is the basis of techniques to determine transmitted power and the conversion of electrical...