Watt-hour Meter

Watt-hour Meter

An electric meter or energy meter is a device that measures the amount of electrical energy supplied to or produced by a residence, business or machine.

The most common type is more properly known as a kilowatt hour meter or a joule meter. When used in electricity retailing, the utilities record the values measured by these meters to generate an invoice for the electricity. They may also record other variables including the time when the electricity was used.

BASIC SINGLE-PHASE METER. A single-phase watt-hour meter is essentially an induction motor whose speed is directly proportional to the voltage applied and the amount of current flowing through it. The phase displacement of the current, as well as the magnitude of the current, is automatically taken into account by the meter. In other words, the power factor influences the speed, and the moving element (disk) rotates with a speed proportional to true power. The register is simply a means of registering revolutions, and by proper gearing is arranged to read directly in kilowatt-hours. (Note: In some cases, the meter reading must be multiplied by a factor called the "register constant" or "meter multiplier" to obtain total kilowatt-hours. See "Register constant (K),

Where:

Sample Problem 1:

The MERALCO test of a 10 A wattmeter having a constant of 0.4, the disk makes 40 revolutions in 53.6 seconds. The average volts and amperes during this period of test are 16 volts and 9.4 A. What is the percent accuracy of the meter at this load?

a. 97.45%

c. 98.07%

b. 98.58%

d. 96.44%

Solution:

Sample Problem 2:

A given ampere-hour meter is under test by connecting it across a 230-V DC source. For a duration of 180 minutes, a constant current of 20 A flows. This meter registers 570.5 and 585.8 kW-hr before and after the test respectively. Calculate the percentage accuracy of the meter.

a. 92.31%

c. 91.44%

b. 90.02%

d. 89.20%

Solution:

Sample Problem 3:

A 15 A, 120-V watt-hour meter has a disk constant of 2. When tested on a unity power factor load, 24 disk revolutions are counted in a period of 2 minutes. How many disk revolutions would be counted per minute if the power were to change 0.5 lagging. Assume the same line current and voltage in both conditions.

a. 6

c. 8

b. 10

d. 12

Solution:

WATTMETER READING USING A PT AND A CT

Where:

Sample Problem 1:

A 115-V, 10 A, three-phase watt-hour meter, having a basic meter constant of k = 2/3 is connected to a three phase, three-wire circuit through a 100:5 ampere CT ratio and 2300:115 volt PT. A time check shows that the meter disk is making 15 revolutions in 50 seconds. What is actual kW of the load?

a. 720 kW

524 kW

b. 288 kW

d. 380 kW

Solution:

Sample Problem 2:

A power plant customer draws power at 220 volts from transformers on a pole. Current transformers with ratio of 200/5 are used to meter the electrical usage. What is the multiplier of the kW-hr and demand meters?

a. 40

c. 100

b. 200

d. 80

Solution:

Sample Problem 3:

A current transformer with a turns ratio of 100:5 and a potential transformer with a turns ratio of 10:1 are connected to the current and voltage coils of a single-phase wattmeter measuring power delivered to a load. If the wattmeter reading is 240 W, what is the actual power measured delivered to the load?

a. 50,000 Watts

c. 48,000 Watts

b. 42,000 Watts

d. 45,000 Watts

Solution:

Signal generatorAn electronic test instrument that delivers an accurately calibrated signal at frequencies from the audio to the microwave ranges. It is valuable in the development and testing of electronic hardware. The signal generator provides a signal that can be adjusted according to frequency, output voltage, impedance, waveform, and modulation.

A signal generator, also known variously as a test signal generator, function generator, tone generator, arbitrary waveform generator, digital pattern generator or frequency generator is an electronic device that generates repeating or non-repeating electronic signals (in either the analog or digital domains). They are generally used in designing, testing, troubleshooting, and repairing electronic or electro-acoustic devices; though they often have artistic uses as well.

There are many different types of signal generators, with different purposes and applications (and at varying levels of expense); in general, no device is suitable for all possible applications.

Traditionally, signal generators have been embedded hardware units, but since the age of multimedia-PCs, flexible, programmable software tone generators have also been available.

General purpose signal generators

Function generators

A function generator is a device which produces simple repetitive waveforms. Such devices contain an electronic oscillator, a circuit that is capable of creating a repetitive waveform. (Modern devices may use digital signal processing to synthesize waveforms, followed by a digital to analog converter, or DAC, to produce an analog output). The most common waveform is a sine wave, but sawtooth, step (pulse), square, and triangular waveform oscillators are commonly available as are arbitrary waveform generators (AWGs). If the oscillator operates above the audio frequency range (>20 kHz), the generator will often include some sort of modulation function such as amplitude modulation (AM), frequency modulation (FM), or phase modulation (PM) as well as a second oscillator that provides an audio frequency modulation waveform.

function generators are typically used in simple electronics repair and design; where they are used to stimulate a circuit under test. A device such as an oscilloscope is then used to measure the circuit's output. Function generators vary in the number of outputs they feature, frequency range, frequency accuracy and stability, and several other parameters.

Arbitrary waveform generators

Arbitrary waveform generators, or AWGs, are sophisticated signal generators which allow the user to generate arbitrary waveforms, within published limits of frequency range, accuracy, and output level. Unlike function generators, which are limited to a simple set of waveforms; an AWG allows the user to specify a source waveform in a variety of different ways. AWGs are generally more expensive than function generators, and are often more highly limited in available bandwidth; as a result, they are generally limited to higher-end design and test applications.

Special purpose signal generators

In addition to the above general-purpose devices, there are several classes of signal generators designed for specific applications.

Tone generators and audio generators

A tone generator is a type of signal generator optimized for use in audio and acoustics applications. Tone generators typically include sine waves over the audio frequency range (20 Hz20 kHz). Sophisticated tone generators will also include sweep generators (a function which varies the output frequency over a range, in order to make frequency-domain measurements), multitone generators (which output several tones simultaneously, and are used to check for intermodulation distortion and other non-linear effects), and tone bursts (used to measure response to transients). Tone generators are typically used in conjunction with sound level meters, when measuring the acoustics of a room or a sound reproduction system, and/or with oscilloscopes or specialized audio analyzers.

Many tone generators operate in the digital domain, producing output in various digital audio formats such as AES-3, or SPDIF. Such generators may include special signals to stimulate various digital effects and problems, such as clipping, jitter, bit errors; they also often provide ways to manipulate the metadata associated with digital audio formats.

The term synthesizer is used for a device that generates audio signals for music, or that uses slightly more intricate methods.

Video signal generators

A video signal generator is a device which outputs predetermined video and/or television waveforms, and other signals used to stimulate faults in, or aid in parametric measurements of, television and video systems. There are several different types of video signal generators in widespread use. Regardless of the specific type, the output of a video generator will generally contain synchronization signals appropriate for television, including horizontal and vertical sync pulses (in analog) or sync words (in digital). Generators of composite video signals (such as NTSC and PAL) will also include a colorburst signal as part of the output. Video signal generators are available for a wide variety of applications, and for a wide variety of digital formats; many of these also include audio generation capability (as the audio track is an important part of any video or television program or motion picture).Application Notes

EZ Terminal Software for Vista, XP and Win2000Signal Forge EZ Terminal for Windows

Serial Communication Software for the Signal Forge Signal GeneratorsSignal Forge EZ Terminal program for Windows. EZ Terminal is and easy to use serial communication software utility for the SF1000. EZ Terminal provides support for macros, terminal window screen capture, downloading firmware (Wave Manager software for the SF1000), and downloading arbitrary waveform descriptor files. EZ Terminal is similar to the well known Windows HyperTerminal program. 3-in-1 Signal GeneratorThe Signal Forge 800/1000 Digitally Synthesized Signal Generator combines the features of both a signal source, signal generator and function generator in a single, low-cost device. In addition, the SF800/1000 incorporates features which make it ideal for testing differential systems, such as high speed serial busses, analog and digital circuits, and RF and telecommunication equipment.

Compensating for External Signal LossIn any RF or analog test setup, there is likely to be signal loss due to cables, attenuators, filters or switches between your source, the Signal Forge 1000 or 800, and the device under test (DUT). The accuracy of the signal level that arrives at the DUT is affected by the sum of these components. This application note describes how to measure the signal loss and how to compensate for for it using the embedded Wave Manager software. Controlling The SF1000 With An External ProgramIn some cases it is necessary to control the Signal Forge 1000 (SF1000) programmatically using an external application or controller. This document describes how to create and use an external control file to operate the SF1000. Controlling The SF1000 Externally - Sample FileThis sample file may be used as a guide in developing a program to control the SF1000 externally. See the "Controlling the SF1000 With An External Program" form more information. Converting LVPECL to LVDS and CMLThe Signal Forge Digitally Synthesized Signal Generator provides a differential clock output that conforms to the LVPECL standard. While LVPEC is a widely used standard, there are other differential signaling standards in use today including LVDS and CML. This application note addresses how to interface the LVPECL differential output of the SF800/1000 to conform to the LVDS and CML standards.

External Clock Requirements for the "E" Model

The SF800E/1000E are designed to operate only when and an external 10 MHz digital clock source is attached. (For applications where an external clock source is not available, the SF800/1000 should be used.)

This document defines the requirements for the external 10 MHz reference clock source. Generating Spectrally Clean OutputThe SF800 and SF1000 Signal Generators provides an AC coupled output that can source a sinusoidal output in the range of 100 KHz to 1 GHz. This output provides a signal with harmonics at least 20 dB down (from 300 MHz to 1 GHz) at programmable output power levels. If a cleaner sinewave signal is needed, for example to drive the LO, or a receiver mixer, an external filter may be attached as described in this application note. I & Q OutputWhile the Signal Forge 800/1000 does not produce I & Q outputs directly, an external splitter may be used to derive the in-phase and quadrature components from the AC-coupled output. This application note describes how to design an external I & Q splitter. Increasing or Decreasing the Signal Generator's Output PowerThe Signal Forge 800/1000 provides an AC coupled frequency source output with a range of 11 dBm to +7 dBm. By adding an external amplifier or an attenuator to increase or decrease power respectively, the amplitude range may be extended.

Power Conversion TableThis application note provides a conversion between dBm, mW and mV for the entire power range of the Signal Forge 1000.

Signal Generators as Alternative to BER TestersThe traditional method of design margin testing in serial data communication systems is to employ a specially designed bit error rate (BER) tester. While BER testers have proven effective, they are typically expensive and they do not always exercise the system under test with the same level of noise or using the same data patterns that will be seen by the system in the field.This article discusses a test methodology, using signal generators, that may be applied to a wide range of data communication systems and devices which transmit data over a serial bus. This test methodology may be part of the design verification process or it may be used to qualify substitute components after the product has been released to production. In this case, the signal generators uncovered a latent design flaw that had not been detected using a BER tester. Software Update ProcedureThe embedded operating software of the Signal Forge 1000 and 800 Signal Generators may be updated in the field by following the procedure described in this document. Any available software updates may be on the Support page of the Signal Forge web site www.signalforge.com.

Testing Amplifiers with the Signal Forge 1000This application note describes a low-cost way to test amplifiers for gain as well as for the 1dB compression point.

Testing Digital SystemsThe Signal Forge 1000 / 800 may be used to test the design margins of a digital system by varying the clock input to the system from min to max. This test ensures that the design maintains the required setup and hold times under all conditions.

Testing High-Speed Serial BussesProper operation of high-speed serial busses requires that data integrity be maintained between the two devices under test (eg. a disk controller and a disk drive) even though these devices are not being driven from the same clock source. Since operation and compatibility must be guaranteed across a range of frequency variations and manufacturing variances, it is imperative to test many device samples under varying conditions. This application note discusses how to configure a test serial bus device using the Signal Forge 1000 or Signal Forge 800.

Testing IP3 with the Signal Forge 1000 and 800This application note describes how to build a low-cost IP3 tester for amplifiers.

Testing Wireless Data Transmission SystemsAmplitude Shift Keying (ASK) and On/Off Keying (OOK) are two techniques used to test and exercise digital data transmission systems such as wireless security systems, keyless entry systems and garage door openers. This application note describes how to use the ASK and OOK waveform modulation functions of the Signal Forge 1000 Signal Generator for testing wireless digital data transmission systems. USB to Serial Adapter Keyspan's USB - Serial adapter makes the Signal Forge 1000 or Signal Forge 800 Signal Generator accessible from a USB port.

The Keyspan USB Serial adapter model 19HS may be purchased online directly from the Keyspan web site:OscilloscopeAn oscilloscope (commonly abbreviated to scope or O-scope) is a type of electronic test equipment that allows signal voltages to be viewed, usually as a two-dimensional graph of one or more electrical potential differences (vertical axis) plotted as a function of time or of some other voltage (horizontal axis). The oscilloscope is one of the most versatile and widely-used electronic instruments. [1]Oscilloscopes are widely used when it is desired to observe the exact wave shape of an electrical signal. In addition to the amplitude of the signal, an oscilloscope can measure the frequency, show distortion, and show the relative timing of two related signals. Oscilloscopes are used in the sciences, medicine, engineering, telecommunications, and industry. General-purpose instruments are used for maintenance of electronic equipment and laboratory work. Special-purpose oscilloscopes may be used for such purposes as adjusting an automotive ignition system, or to display the waveform of the heartbeat.

Originally all oscilloscopes used cathode ray tubes as their display element, but modern digital oscilloscopes use high-speed analog-to-digital converters and computer-like display screens and processing of signals. Oscilloscope peripheral modules for general purpose laptop or desktop personal computers can turn them into useful and flexible test instruments.

What does an oscilloscope do?

An oscilloscope is easily the most useful instrument available for testing circuits because it allows you to see the signals at different points in the circuit. The best way of investigating an electronic system is to monitor signals at the input and output of each system block, checking that each block is operating as expected and is correctly linked to the next. With a little practice, you will be able to find and correct faults quickly and accurately.

An oscilloscope is an impressive piece of kit:

The diagram shows a Hameg HM 203-6 oscilloscope, a popular instrument in UK schools. Your oscilloscope may look different but will have similar controls.

Faced with an instrument like this, students typically respond either by twiddling every knob and pressing every button in sight, or by adopting a glazed expression. Neither approach is especially helpful. Following the systematic description below will give you a clear idea of what an oscilloscope is and what it can do.

The function of an oscilloscope is extremely simple: it draws a V/t graph, a graph of voltage against time, voltage on the vertical or Y-axis, and time on the horizontal or X-axis.

As you can see, the screen of this oscilloscope has 8 squares or divisions on the vertical axis, and 10 squares or divisions on the horizontal axis. Usually, these squares are 1cm in each direction:

Many of the controls of the oscilloscope allow you to change the vertical or horizontal scales of the V/t graph, so that you can display a clear picture of the signal you want to investigate. 'Dual trace' oscilloscopes display two V/t graphs at the same time, so that simultaneous signals from different parts of an electronic system can be compared.

Function of an oscilloscope

The function of an oscilloscope is to be able to display waveforms on some form of display. In the normal mode of operation time is displayed along the X-axis (horizontal axis) and amplitude is displayed along the Y axis (vertical axis). In this way it is possible to see an electronic waveform on an oscilloscope as it may be envisaged. The waveform could be likened to that of the ripples on traveling along the surface of a pond when a stone is dropped into it.

Features and usesBy seeing a waveform in this manner it is possible to see analyze the operation of the circuit and discover why any problems may exist.

Oscilloscope exterior

An oscilloscope will normally have a large array of items on the exterior of the case. The font panel will typically have a number of items on it:

1. Display The first things that is noticed on an oscilloscope is the large display that is used for displaying the waveform. This typically may take around a quarter of the space on the front panel or even a little more. It is often good to have a reasonably large display then it is easier to see the various elements of the waveform.

2. Connectors There is a variety of different connectors on the front panel. Typically there is an input for each of the channels to be displayed - often an oscilloscope will have more than one channel. Many oscilloscopes are dual channel and can therefore display two signals at the same time, allowing waveforms to be compared. Other inputs may include a trigger input that will enable the trace on the oscilloscope to be triggered according to this signal.

3. Controls There is a variety of controls on the oscilloscope:

Vertical gain / signal input sensitivity: This is generally calibrated in V/cm, i.e. each vertical division on the scale represents a given number of volts.

Timebase: This alters the speed at which the trace crosses the screen horizontally on the oscilloscope. It is calibrated in terms of time / division, e.g. 1ms / cm, assuming the divisions are at one centimetre intervals.

Trigger: The controls that are associated with the trigger enable the timebase of the oscilloscope to be triggered in various ways. This enables a still or stable picture to be obtained on the screen of the oscilloscope.

In order to be able to operate the oscilloscope correctly it is necessary to connect the right signals into the inputs, and also to use the controls correctly.

Operating an oscilloscope

Like any other piece of complicated test equipment, an oscilloscope can take a few minutes to get used to if one has not been used before. However once familiar with it, the controls soon become second nature and it becomes very easy to use.

It is obviously necessary to turn the oscilloscope power on, and then once it is running it may be necessary to adjust the intensity of the trace so that it is easily visible - often oscilloscopes will free run when no signal is present. If the oscilloscope does not free run, then no trace will be seen yet.

Then the next control to set is the vertical gain control. Set is so that the anticipated waveform will fill a reasonable amount of the screen. Leave some margin so that if it is bigger than expected, it will not go wildly off the screen.

Next set the time base of the oscilloscope. This is often set so that a period of the waveform will fill most of the horizontal axis of the screen. If it is initially set to this then it can be adjusted to suit later.

Connect the signal to be viewed. The oscilloscopes will posses a connector for the input - this is normally a BNC connector. In most cases where a connection to a circuit board is required, a scope probe will be used, so that they are easy to connect to pins or connection points on the board.

With the signal now present it is necessary to adjust the trigger control to gain a stable trace of the signal.

With a trace of the signal now visible, the vertical gain and timebase controls can be re-adjusted to produce the best picture of the signal.

Although these instructions do not give an exhaustive description of how to use an oscilloscope, the exact number of controls and operation will depend upon the particular scope in use. However they should enable the scope to be used in a basic but reasonable manner.

SIGNAL GENERATORS and

OSCILLOSCOPE CALIBRATIONThis paper shows how standard signal generators can be used as leveled sine wave sources for calibrating oscilloscopes. To do so, it is necessary to show that signal generator specifications match, or can be made to match, oscilloscope calibration requirements. Assume that oscilloscope calibration equipment is currently in place and performs adequately, including leveled sine wave performance up to 500 Mhz. Also assume a need to increase the frequency capability of the leveled sine wave source for new, higher frequency, oscilloscopes. A good place to start looking at performance requirements for a signal generator is the performance of existing calibration equipment. The Tektronix SG 5030 is a commonly used leveled sine wave generator.

SG 5030 specificationsFrequency

0.1 Hz to 550 MHz

Frequency accuracy

+/- 3 ppm

Amplitude Range

4.5 mvpp to 5.5 Vpp

Amplitude accuracy

from 0.1 Hz to 50 kHz --- +/- 1.5 % of setting

Flatness (relative to 50 kHz amplitude)

+/- 1.5 % from 50 kHz to 100 Mhz

+/- 3 % from 100 Mhz to 250 Mhz

+/- 4 % from 250 Mhz to 550 Mhz

VSWR

< 1.2:1

Harmonic distortion

all