Discussion on Electric Power Measurement

Discussion on Electric Power Measurement
http: // 2007-7-20 Beijing Ocean Industrial Technology Co., Ltd.

From a large perspective, power measurement is required in many fields, and the methods of power measurement in different fields are very different. For example, in the field of communication, it is necessary to test the transmission power, transmission power, and reception power of the receiving device of the transmitting device (such as the antenna). Most of the test signals here are radio frequency signals, which are invisible and intangible. The measurement generally needs to use the antenna to receive, and the frequency point or frequency band needs to be set before receiving, and then the power measurement is performed. In the field of power testing, the signal frequency is low, and the power is generally calculated by measuring its voltage, current, resistance, etc., and there are many instruments for testing these basic parameters, such as multimeters, oscilloscopes, etc., and power can also be tested by power. Measured directly. This article mainly introduces the power measurement in the field of power testing.
1. How many power definitions are there?
In the IEEE Technical Dictionary, there are more than ten different power definitions, two of which are the most commonly used power types: apparent power S, average power P (also known as true power, active power). There are many other definitions of power, such as reactive power Q, harmonic power, instantaneous power, etc. Common power expressions are shown in Table 1.

name

inspecting power

Average power (active power, true power)

definition

In an AC circuit with impedance, the product of the effective value of voltage and the effective value of current is called "apparent power"

The instantaneous power of alternating current is not a constant value, the average value of power in a cycle is called active power

formula

Urms is the effective value of voltage, Irms is the effective value of current

Urms is the effective value of voltage, Irms is the effective value of current, φ is the phase angle between sinusoidal AC voltage U and current I, cosφ power factor, only valid for sine wave

unit

VA

W

Remarks

In AC circuits, due to inductive or capacitive energy storage devices, there is a phase difference between the voltage and the current. Generally speaking, the voltage and the current do not arrive at the same time. Big work, there is energy conversion between power supply and energy storage equipment; so it is called apparent power.

1. The average power of a non-sinusoidal AC circuit

Among them, Un is the voltage measurement value including the harmonic voltage, In is the current measurement value including the harmonic current, PF is the power factor, and is generally used for non-sinusoidal waveforms. The difference from the above definition is that the higher harmonics of n are included, and a discrete calculation method is used.
Another definition of average power is the definition of "thermal energy" in the equivalent DC resistance, which is a concept that is easier to understand

2. The importance of average power
For resistive loads such as light bulbs, heaters, etc., the average power measurement and calculation is very convenient, but such calculations are not applicable to non-linear loads. In modern electronic technology applications, switching power supplies, electronic rectifiers, air-conditioning control systems, induction or pulse modulation motors, etc. all use non-linear technologies. In this way, the average power of non-linear loads is required in design, fault diagnosis and analysis measuring.
As shown above, for the measurement of power, it is necessary to measure basic parameters such as voltage, current, resistance, etc., but for the testing of these parameters, you need to pay attention to the definition method, for example, there are many definitions of voltage parameters: voltage instantaneous value, voltage Mean square value, voltage setting value, voltage effective value, voltage peak value, etc. Below, we introduce the definition methods of these parameters one by one.
2. Definition of multiple parameters
1. arithmetic mean

The arithmetic average value of a periodic signal is the average value of the signal in a period T, which is equivalent to the DC component of the signal. If the average value is equal to 0, the signal is a pure AC signal. For DC signals, the average value is the same as the instantaneous value. For signals containing both AC and DC components, the average value is the DC component.
2. Setting value

Skin Care

Skin Care,Face Moisturizer,Hydrating Cleanser,Moisturizer For Oily Skin

Guangzhou cosmeceuticals daily chemicals PTY,.LTD. , https://www.guangzhoucosmetics.com