The Philosophy and Consequence of Measurement – Power

Power - The Philosophy and Consequence of Measurement

Published: 11th March 2014

‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’. Lord Kelvin

We continue looking into the need and specifications for test equipment by looking at 6Ps (Precision, Power, Performance) - (Productivity, Portability, Package) and from our previous writings on Precision we move to look at Power and we’ll begin with various Tweets from Mobile World Congress #MWC14

- Power Saving Mode; Ultra Power Saving Mode;
- more power, more pixels, and a refined design
- Flex phone needs a flexible wireless power station
- demos the power of GSMA
- new power management tech for better battery life when streaming at #LTE speeds
- The power of mm wave with the efficiency of point to multipoint backhaul
- chipsets deliver brighter images using less power in phones & more
- Maximizes Wireless Network Connectivity With New Power Amplifier
- enable up to 40+% performance, 30% lower power and 100+% battery life with 28nm collaboration
- solved power consumption and heat issue with snapdragon chip

All of this clearly demonstrates that within the mobile world there is the continuing battle of more data (energy) versus the lower power consumption. Nobody wants to hold a hot brick to their ear!

We demand that our smartphones and other net-workable handheld devices use every last bit of battery life to remain connected.

When using a smartphone or tablet to access the internet, you often have a choice between using WiFi or 3G to connect. In general, however, networking using WiFi causes less drain on your device's battery than connecting with 3G. That’s because both 3G and WiFi waste "tail energy" when completing data transfers. Devices must use more power to transfer data and there is a short period after each transfer when the device is still at a higher power setting. This power loss is unavoidable and it will occur regardless of the networking method you choose. Both 3G and WiFi waste some power after completing a data transfer, WiFi is "significantly more efficient than 3G therefore, a WiFi download will use less energy overall than an identical 3G download.

Therefore the quest for more data at less power consumption drives the demand for more and more accuracy, precision and capability of power measurement. The consequences of a simple fundamental measurement increase.

We’ll continue in next article with more on Power measurement.

Rejoice in your measurements. Demand more and enjoy this series.

The Philosophy and Consequence of Measurement - Power Part 2

‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’. Lord Kelvin

We continue looking into the need and specifications for test equipment by looking at 6Ps (Precision, Power, Performance) - (Productivity, Portability, Package) and from Precision we continue our look at Power measurements which is basically how much oomph a system needs to carry the quantity as far and as for long as needed.

We’ll split these in two (without a divider)

- Electrical Power Measurements which can be measured with some form of DMM or Oscilloscope; clamp; Wattmeter
- Spectral Power Measurements using a Power meter or Spectrum Analyser

In this article we’ll specifically glance at Electrical Power Measurements

Resistive:- For DC circuits and purely-resistive AC circuits, power is the product of voltage and . You first measure the volts then the current and multiply the two that will be your power, say 220 Volt multiplied with 5.9090909 amps = 1300 watts or 1.3 kW. kW = kilowatts.

Reactive:- For reactive AC circuits, the product of voltage and current is termed Apparent Power, which is measured in volt amperes (symbol: V.A). To measure the true power of reactive AC circuits, in Watts, one needs to take into account the circuit's power factor, which is the cosine of the angle by which the current leads or lags the supply voltage.

A typical power measurement requires one measurement device to capture the voltage across the terminals of a load, and the second device to capture the current going through the load. However, the actual power calculation depends on the resistive and reactive components (capacitors and/or inductors) in the circuit. The power dissipation in a purely resistive circuit is always a function of the voltage drop and current draw through the circuit.

Reactive circuits appear to function like resistive circuits because they produce voltage drops and draw current. However, reactive circuits actually store or return power. The reactive components cause a phase shift (up to 90 degrees) between the voltage and current waveforms which reduces the overlap between the two curves and effectively delivers less power to the loads. This phenomenon is represented by three different power measurements: reactive power, apparent power, and real power. These three power measurements have a phase relationship that can be visualised as a power triangle.

Apparent Power:- is the measure of a circuit’s impedance (Z) and is represented by an S, which has a unit measure of Volt-Amps (VA). Apparent power is the combination of reactive power and real power, without reference to a phase angle. You calculate apparent power by using the formula: Apparent Power (S) = Vrms * Irms

The pursuit of measurement of absolute power will come next where in our world absolute power does not corrupt absolutely but absolute power has inherent corruption.

Ref John Dalberg-Acton, 1st Baron Acton

We’ll discuss that next. Do leave your comments and inputs. These articles are solely an opinion on the measurements we are interested in.

Rejoice in your measurements. Demand more and enjoy this series.

The Philosophy and Consequence of Measurement - Power Part 3

‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’. Lord Kelvin

We continue looking into the need and specifications for test equipment by looking at 6Ps (Precision, Power, Performance)- (Productivity, Portability, Package) and from Precision we continue our look at Power measurements which is basically how much oomph a system needs to carry the quantity as far and as for long as needed.

We split these in two (without a divider)

- Electrical Power Measurements which can be measured with some form of DMM or Oscilloscope; clamp; Wattmeter
- Spectral Power Measurements using a Power meter or Spectrum Analyser

So, in this article we’ll specifically look at Spectral Power or the Power Spectrum. How can our measurement device actually answer the question ‘How much of the signal is at a frequency of x?’ and therefore we are most likely to be using a Power Meter or Spectrum Analyser

We could also be looking at a variety of different signals

- Periodic signals which give peaks at a fundamental and its harmonics;
- Quasiperiodic signals which give peaks at linear combinations of two or more
- Irrationally related frequencies (often giving the appearance of a main sequence and sidebands)
- Chaotic dynamics which give broad band components to the spectrum.

These however are all statements about the ideal power spectrum, if infinitely long sequences of continuous data are available to process. In practice there are always limitations of restricted data length and sampling frequency, and it is important to investigate how these limitations affect the appearance of the power spectrum.

So, in essence we’d be looking to measure the averaged power spectrum of an input signal and in practise using various averaging modes such as RMS averaging, vector averaging, or peak hold, as well as the number of averages. You would then be able to observe the influence of these averaging parameters, typically on the noise floor, and notice that vector averaging requires the use of a trigger in order to lower the noise floor without lowering the fundamental along with it.

To assist us in that quest we’d be looking for an accurate measurement device with the correct range and the correct functionalities for us as engineers to apply our skills to hone in on the signal in question and best describe it to make informed decisions.

What the measurement of power in a spectrum tells us and what decisions it enables us as engineers to make we’ll discuss in our next article.

Please leave your comments and inputs. These articles are solely an opinion on the measurements we are interested in.

Rejoice in making your measurements. Demand more in measurement and enjoy this series.

The Philosophy and Consequence of Measurement - Power Part 4

‘When you cannot measure… your knowledge is of a meagre and unsatisfactory kind’. Lord Kelvin

We continue looking into the need and specifications for test equipment by looking at 6Ps (Precision, Power, Performance) - (Productivity, Portability, Package) and from Precision we continue our look at Power measurements which is basically how much oomph a system needs to carry the quantity as far and as for long as needed.

We split these in two (without a divider)

- Electrical Power Measurements which can be measured with some form of DMM or Oscilloscope; clamp; Wattmeter
- Spectral Power Measurements using a Power meter or Spectrum Analyser

And now we look into what the measurement of power in a spectrum tells us and what decisions it enables us as engineers.

The basics:- When a signal contains only one frequency (i.e. it is sinusoidal) determining that frequency, its amplitude and phase can be a straightforward process. However, real signals are usually not sinusoidal, contain many frequencies and may contain random elements. Determining the frequency content of such a signal requires more sophisticated methods.

Communication systems and data processing systems are required to handle an ever increasing number and variance of signals in the presence of and near to noise. The capacity and demand for more and more information as data, words and video is increasing daily.

To satiate this demand we must work nearer and nearer to limits once only dreamt of. Nearer to the noise floor and more within the presence of noise.

With that comes the demand and challenge of even more precise measurement and the need for sophisticated measurement tools.

Today’s basic spectrum analyser is awash with added functionality and the specification of high performance instrumentation is breathtaking. Just take a look at the range available here from MCS Test Equipment.

From cellular to cordless to wireless LAN (WLAN) systems, spectrum is a vital component in the system design process. Measuring power is important for circuit designers as well. Most communications systems fall into one of two technology categories:

1. Bandwidth Efficient, the ability of a modulation scheme to accommodate data within a limited bandwidth, or
2. Power Efficient, the ability of the system to reliably send information at the lowest practical power level.

For designers of some digital terrestrial microwave radios a high priority is good bandwidth efficiency with low bit-error-rate. They have plenty of power available and are not too concerned with power efficiency .

On the other hand, designers of mobile phones put a high priority on power efficiency because, quite simply, the phones run on a battery.

Every time one of these efficiency parameters (bandwidth or power) is increased, the other can decrease, or become more complex or less efficient.

The radio spectrum is very valuable and operators who do not use the spectrum efficiently lose out in a highly competitive market.

Through the demand for higher data security, better quality communications, and quicker system availability developers today face the constraints of available bandwidth, permissible power and inherent noise level of the system. The RF spectrum must be shared, yet every day there are more users for that spectrum as demand for communications services increases. Therefore the ‘simple’ measurement of power spectra is a problem of steadily increasing importance.

The idea of obtaining a spectrum from a measurement may therefore at times seem overwhelming, not least because signals in the natural world can contain infinitely many frequencies. However, such continuous signals can also be broken into infinitely many time steps and we can measure their behaviour in time by sampling them at regular intervals over some limited time.

In an exactly analogous way, measuring a spectrum is an exercise in sampling it at regular intervals in frequency over a limited frequency range. To understand how this comes about we need to consider the whole measurement process and have confidence in the instrumentation we are using and who we have bought it from.

Next we look at Performance as it relates to the instrumentation we are using and looking for.

Please leave your comments and inputs. These articles are solely an opinion on the measurements we are interested in.

Rejoice in making your measurements. Demand more in measurement and enjoy this series.

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