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Work-analyzer, power meter and transient recorder. User-friendliness was one of the main objectives of the device development. The PQ-100 Box has been developed for mobile oper-ation (degree of protection IP65); it is applicable for measurements in public networks (CAT IV) as well as for measurements in industrial environment up to. A network analyzer is an instrument that measures the network parameters of electrical networks.Today, network analyzers commonly measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, and h-parameters. Power Quality Analyser PQ-Box 100 / Power Quality Software. File: BAPQBox100EN201803.pdf. Version: 03/2018. Category: for mobile analyzers. Document Languages: EN.

10 MHz to 50 GHz network analyzer, 2-ports. 104 dB of dynamic range and; 0.006 dB trace noise; 26 usec/point measurement speed, 32 channels, 16,001 points. Network analyzers, are much more generalpurpose in nature. Network analyzers can measure both linear and nonlinear behavior of devices, although the measurement techniques are different (frequency versus power sweeps for example). This module focuses on swept-frequency and swept-power measurements made with network analyzers.

ZVA40 vector network analyzer from Rohde & Schwarz.

A network analyzer is an instrument that measures the network parameters of electrical networks. Today, network analyzers commonly measure s–parameters because reflection and transmission of electrical networks are easy to measure at high frequencies, but there are other network parameter sets such as y-parameters, z-parameters, and h-parameters. Network analyzers are often used to characterize two-port networks such as amplifiers and filters, but they can be used on networks with an arbitrary number of ports.

## Overview

Network analyzers are used mostly at high frequencies; operating frequencies can range from 1 Hz to 1.5 THz.[1] Special types of network analyzers can also cover lower frequency ranges down to 1 Hz.[2] These network analyzers can be used for example for the stability analysis of open loops or for the measurement of audio and ultrasonic components.[3]

The two basic types of network analyzers are

• scalar network analyzer (SNA)—measures amplitude properties only
• vector network analyzer (VNA)—measures both amplitude and phase properties

A VNA is a form of RF network analyzer widely used for RF design applications. A VNA may also be called a gain-phase meter or an automatic network analyzer. An SNA is functionally identical to a spectrum analyzer in combination with a tracking generator. As of 2007, VNAs are the most common type of network analyzers, and so references to an unqualified 'network analyzer' most often mean a VNA. Five prominent VNA manufacturers are Keysight, Anritsu, Rohde & Schwarz, Copper Mountain Technologies and OMICRON Lab.

Another category of network analyzer is the microwave transition analyzer (MTA) or large signal network analyzer (LSNA), which measure both amplitude and phase of the fundamental and harmonics. The MTA was commercialized before the LSNA, but was lacking some of the user-friendly calibration features now available with the LSNA.

## Architecture

The basic architecture of a network analyzer involves a signal generator, a test set, one or more receivers and display. In some setups, these units are distinct instruments. Most VNAs have two test ports, permitting measurement of four S-parameters (${displaystyle S_{11},}$, ${displaystyle S_{21},}$, ${displaystyle S_{12},}$ and ${displaystyle S_{22},}$), but instruments with more than two ports are available commercially.

### Signal generator

The network analyzer needs a test signal, and a signal generator or signal source will provide one. Older network analyzers did not have their own signal generator, but had the ability to control a stand-alone signal generator using, for example, a GPIB connection. Nearly all modern network analyzers have a built-in signal generator. High-performance network analyzers have two built-in sources. Two built-in sources are useful for applications such as mixer test, where one source provides the RF signal, another the LO; or amplifierintermodulation testing, where two tones are required for the test.

### Test set

The test set takes the signal generator output and routes it to the device under test, and it routes the signal to be measured to the receivers. It often splits off a reference channel for the incident wave. In a SNA, the reference channel may go to a diode detector (receiver) whose output is sent to the signal generator's automatic level control. The result is better control of the signal generator's output and better measurement accuracy. In a VNA, the reference channel goes to the receivers; it is needed to serve as a phase reference.

Directional couplers or two resistor power dividers are used for signal separation. Some microwave test sets include the front end mixers for the receivers (e.g., test sets for HP 8510).

The receivers make the measurements. A network analyzer will have one or more receivers connected to its test ports. The reference test port is usually labeled R, and the primary test ports are A, B, C,.... Some analyzers will dedicate a separate receiver to each test port, but others share one or two receivers among the ports. The R receiver may be less sensitive than the receivers used on the test ports.

For the SNA, the receiver only measures the magnitude of the signal. A receiver can be a detector diode that operates at the test frequency. The simplest SNA will have a single test port, but more accurate measurements are made when a reference port is also used. The reference port will compensate for amplitude variations in the test signal at the measurement plane. It is possible to share a single detector and use it for both the reference port and the test port by making two measurement passes.

For the VNA, the receiver measures both the magnitude and the phase of the signal. It needs a reference channel (R) to determine the phase, so a VNA needs at least two receivers. The usual method down converts the reference and test channels to make the measurements at a lower frequency. The phase may be measured with a quadrature detector. A VNA requires at least two receivers, but some will have three or four receivers to permit simultaneous measurement of different parameters.

There are some VNA architectures (six-port) that infer phase and magnitude from just power measurements.

### Processor and display

With the processed RF signal available from the receiver / detector section it is necessary to display the signal in a format that can be interpreted. With the levels of processing that are available today, some very sophisticated solutions are available in RF network analyzers. Here the reflection and transmission data is formatted to enable the information to be interpreted as easily as possible. Most RF network analyzers incorporate features including linear and logarithmic sweeps, linear and log formats, polar plots, Smith charts, etc. Trace markers, limit lines and pass/fail criteria are also added in many instances.[4]

## S-parameter measurement with vector network analyzer

The basic parts of a vector network analyzer

A VNA is a test system that enables the RF performance of radio frequency and microwave devices to be characterised in terms of network scattering parameters, or S parameters.

The diagram shows the essential parts of a typical 2-port vector network analyzer (VNA). The two ports of the device under test (DUT) are denoted port 1 (P1) and port 2 (P2). The test port connectors provided on the VNA itself are precision types which will normally have to be extended and connected to P1 and P2 using precision cables 1 and 2, PC1 and PC2 respectively and suitable connector adaptors A1 and A2 respectively.

The test frequency is generated by a variable frequency CW source and its power level is set using a variable attenuator. The position of switch SW1 sets the direction that the test signal passes through the DUT. Initially consider that SW1 is at position 1 so that the test signal is incident on the DUT at P1 which is appropriate for measuring ${displaystyle S_{11},}$ and ${displaystyle S_{21},}$. The test signal is fed by SW1 to the common port of splitter 1, one arm (the reference channel) feeding a reference receiver for P1 (RX REF1) and the other (the test channel) connecting to P1 via the directional coupler DC1, PC1 and A1. The third port of DC1 couples off the power reflected from P1 via A1 and PC1, then feeding it to test receiver 1 (RX TEST1). Similarly, signals leaving P2 pass via A2, PC2 and DC2 to RX TEST2. RX REF1, RX TEST1, RX REF2 and RXTEST2 are known as coherent receivers as they share the same reference oscillator, and they are capable of measuring the test signal's amplitude and phase at the test frequency. All of the complex receiver output signals are fed to a processor which does the mathematical processing and displays the chosen parameters and format on the phase and amplitude display. The instantaneous value of phase includes both the temporal and spatial parts, but the former is removed by virtue of using 2 test channels, one as a reference and the other for measurement. When SW1 is set to position 2, the test signals are applied to P2, the reference is measured by RX REF2, reflections from P2 are coupled off by DC2 and measured by RX TEST2 and signals leaving P1 are coupled off by DC1 and measured by RX TEST1. This position is appropriate for measuring ${displaystyle S_{22},}$ and ${displaystyle S_{12},}$.

## Calibration and error correction

A network analyzer, like most electronic instruments requires periodic calibration; typically this is performed once per year and is performed by the manufacturer or by a 3rd party in a calibration laboratory. When the instrument is calibrated, a sticker will usually be attached, stating the date it was calibrated and when the next calibration is due. A calibration certificate will be issued.

A vector network analyzer achieves highly accurate measurements by correcting for the systematic errors in the instrument, the characteristics of cables, adapters and test fixtures. The process of error correction, although commonly just called calibration, is an entirely different process, and may be performed by an engineer several times in an hour. Sometimes it is called user-calibration, to indicate the difference from periodic calibration by a manufacturer.

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A network analyzer has connectors on its front panel, but the measurements are seldom made at the front panel. Usually some test cables will connect from the front panel to the device under test (DUT). The length of those cables will introduce a time delay and corresponding phase shift (affecting VNA measurements); the cables will also introduce some attenuation (affecting SNA and VNA measurements). The same is true for cables and couplers inside the network analyzer. All these factors will change with temperature. Calibration usually involves measuring known standards and using those measurements to compensate for systematic errors, but there are methods which do not require known standards. Only systematic errors can be corrected. Random errors, such as connector repeatability cannot be corrected by the user calibration. However, some portable vector network analyzers, designed for lower accuracy measurement outside using batteries, do attempt some correction for temperature by measuring the internal temperature of the network analyzer.

The first steps, prior to starting the user calibration are:

• Visually inspect the connectors for any problems such as bent pins or parts which are obviously off-centre. These should not be used, as mating damaged connectors with good connectors will often result in damaging the good connector.
• Clean the connectors with compressed air at less than 60 psi.
• If necessary clean the connectors with isopropyl alcohol and allow to dry.
• Gage the connectors to determine there are not any gross mechanical problems. Connector gauges with resolutions of 0.001' to 0.0001' will usually be included in the better quality calibration kits.
• Tighten the connectors to the specified torque. A torque wrench will be supplied with all but the cheapest calibration kits.

There are several different methods of calibration.

• SOLT : which is an acronym for Short, Open, Load, Through, is the simplest method. As the name suggests, this requires access to known standards with a short circuit, open circuit, a precision load (usually 50 ohms) and a through connection. It is best if the test ports have the same type of connector (N, 3,5 mm etc.), but of a different gender, so the through just requires the test ports are connected together. SOLT is suitable for coaxial measurements, where it is possible to obtain the short, open, load and through. The SOLT calibration method is less suitable for waveguide measurements, where it is difficult to obtain an open circuit or a load, or for measurements on non-coaxial test fixtures, where the same problems with finding suitable standards exist.
• TRL (through-reflect-line calibration): This technique is useful for microwave, noncoaxial environments such as fixture, wafer probing, or waveguide. TRL uses a transmission line, significantly longer in electrical length than the through line, of known length and impedance as one standard. TRL also requires a high-reflection standard (usually, a short or open) whose impedance does not have to be well characterized, but it must be electrically the same for both test ports.[5]

The simplest calibration that can be performed on a network analyzer is a transmission measurement. This gives no phase information, and so gives similar data to a scalar network analyzer. The simplest calibration that can be performed on a network analyzer, whilst providing phase information is a 1-port calibration (S11 or S22, but not both). This accounts for the three systematic errors which appear in 1-port reflectivity measurements:

• Directivity—error resulting from the portion of the source signal that never reaches the DUT.
• Source match—errors resulting from multiple internal reflections between the source and the DUT.
• Reflection tracking—error resulting from all frequency dependence of test leads, connections, etc.

In a typical 1-port reflection calibration, the user measures three known standards, usually an open, a short and a known load. From these three measurements the network analyzer can account for the three errors above.[6][7]

A more complex calibration is a full 2-port reflectivity and transmission calibration. For two ports there are 12 possible systematic errors analogous to the three above. The most common method for correcting for these involves measuring a short, load and open standard on each of the two ports, as well as transmission between the two ports.

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It is impossible to make a perfect short circuit, as there will always be some inductance in the short. It is impossible to make a perfect open circuit, as there will always be some fringing capacitance. A modern network analyzer will have data stored about the devices in a calibration kit. (Keysight Technologies 2006) For the open-circuit, this will be some electrical delay (typically tens of picoseconds), and fringing capacitance which will be frequency dependent. The capacitance is normally specified in terms of a polynomial, with the coefficients specific to each standard. A short will have some delay, and a frequency dependent inductance, although the inductance is normally considered insignificant below about 6 GHz. The definitions for a number of standards used in Keysight calibration kits can be found at http://na.support.keysight.com/pna/caldefs/stddefs.html The definitions of the standards for a particular calibration kit will often change depending on the frequency range of the network analyzer. If a calibration kit works to 9 GHz, but a particular network analyzer has a maximum frequency of operation of 3 GHz, then the capacitance of the open standard can approximated more closely up to 3 GHz, using a different set of coefficients than are necessary to work up to 9 GHz.

In some calibration kits, the data on the males is different from the females, so the user needs to specify the gender of the connector. In other calibration kits (e.g. Keysight 85033E 9 GHz 3.5 mm), the male and female have identical characteristics, so there is no need for the user to specify the gender. For gender-less connectors, like APC-7, this issue does not arise.

Most network analyzers have the ability to have a user defined calibration kit. So if a user has a particular calibration kit details of which are not in the firmware of the network analyzer, the data about the kit can be loaded into the network analyzer and so the kit used. Typically the calibration data can be entered on the instrument front panel or loaded from a medium such as floppy disk or USB stick, or down a bus such as USB or GPIB.

The more expensive calibration kits will usually include a torque wrench to tighten connectors properly and a connector gauge to ensure there are no gross errors in the connectors.

### Automated calibration fixtures

A calibration using a mechanical calibration kit may take a significant amount of time. Not only must the operator sweep through all the frequencies of interest, but the operator must also disconnect and reconnect the various standards. (Keysight Technologies 2003, p. 9) To avoid that work, network analyzers can employ automated calibration standards. (Keysight Technologies 2003) The operator connects one box to the network analyzer. The box has a set of standards inside and some switches that have already been characterized. The network analyzer can read the characterization and control the configuration using a digital bus such as USB.

## Network analyzer verification kits

Many verification kits are available to verify the network analyzer is performing to specification. These typically consist of transmission lines with an air dielectric and attenuators. The Agilent 85055A kit includes a 10 cm airline, stepped impedance airline, 20 dB and 50 dB attenuators with data on the devices measured by the manufacturer and stored on both a floppy disk and USB flash drive. Older versions of the 85055A have the data stored on tape and floppy disks rather than on USB drives.

## Noise figure measurements

The three major manufacturers of VNAs, Keysight, Anritsu, and Rohde & Schwarz, all produce models which permit the use of noise figure measurements. The vector error correction permits higher accuracy than is possible with other forms of commercial noise figure meters.

## Notes

1. ^Keysight - Network Analyzers, as of 3 Nov 2020
2. ^OMICRON Lab - Network Analyzer Bode 100, as of 3 Nov 2020
3. ^OMICRON Lab Vector Network Analyzer products, as of 3 April 2008
4. ^RF Network Analyzer Operation & Circuit
5. ^Engen, Glenn F.; Hoer, Cletus A. (1979). 'Through-reflect-line: An improved technique for calibrating the dual six-port automatic network analyzer'. IEEE Transactions on Microwave Theory and Techniques. 27 (12): 987–993. doi:10.1109/TMTT.1979.1129778.
6. ^Keysight network analyzer basicshttp://literature.cdn.keysight.com/litweb/pdf/5965-7917E.pdf date=2005-12-23
7. ^Keysight: measurement errors

## References

• Keysight Technologies (June 9, 2003), Electronic vs. Mechanical Calibration Kits: Calibration Methods and Accuracy(PDF), White Paper, Keysight Technologies
• Keysight Technologies (July 13, 2006), Specifying Calibration Standards for the Agilent 8510 Network Analyzer(PDF), Application Note 8510-5B, Keysight Technologies
• Dunsmore, Joel P. (September 2012), Handbook of Microwave Component Measurements: with Advanced VNA Techniques, Wiley, ISBN978-1-1199-7955-5

 Wikimedia Commons has media related to Network analyzers.

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• Network Analyzer Basics (PDF, 5.69 MB), from Agilent
• Primer on Vector Network Analysis (PDF, 123 KB), from Anritsu
• Large-Signal Network Analysis (PDF, 3.73 MB), by Dr. Jan Verspecht
• Homebrew VNA by Paul Kiciak, N2PK
• Measuring Frequency Response (PDF, 961 KB), by Dr Ray Ridley

From 1929[1] to the late 1960s, large alternating current power systems were modelled and studied on AC network analyzers (also called alternating current network calculators or AC calculating boards) or transient network analyzers. These special-purpose analog computers were an outgrowth of the DC calculating boards used in the very earliest power system analysis. By the middle of the 1950s, fifty network analyzers were in operation.[2] AC network analyzers were much used for power flow studies, short circuit calculations, and system stability studies, but were ultimately replaced by numerical solutions running on digital computers. While the analyzers could provide real-time simulation of events, with no concerns about numeric stability of algorithms, the analyzers were costly, inflexible, and limited in the number of buses and lines that could be simulated.[3] Eventually powerful digital computers replaced analog network analyzers for practical calculations, but analog physical models for studying electrical transients are still in use.

## Calculating methods

As AC power systems became larger at the start of the 20th century, with more interconnected devices, the problem of calculating the expected behavior of the systems became more difficult. Manual methods were only practical for systems of a few sources and nodes. The complexity of practical problems made manual calculation techniques too laborious or inaccurate to be useful. Many mechanical aids to calculation were developed to solve problems relating to network power systems.

DC calculating boards used resistors and DC sources to represent an AC network. A resistor was used to model the inductive reactance of a circuit, while the actual series resistance of the circuit was neglected. The principle disadvantage was the inability to model complex impedances. However, for short-circuit fault studies, the effect of the resistance component was usually small. DC boards served to produce results accurate to around 20% error, sufficient for some purposes.

Artificial lines were used to analyze transmission lines. These carefully constructed replicas of the distributed inductance, capacitance and resistance of a full-size line were used to investigate propagation of impulses in lines and to validate theoretical calculations of transmission line properties. An artificial line was made by winding layers of wire around a glass cylinder, with interleaved sheets of tin foil, to give the model proportionally the same distributed inductance and capacitance as the full-size line. Later, lumped-element approximations of transmission lines were found to give adequate precision for many calculations.

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Laboratory investigations of the stability of multiple-machine systems were constrained by the use of direct-operated indicating instruments (voltmeters, ammeters, and wattmeters). To ensure that the instruments negligibly loaded the model system, the machine power level used was substantial. Some workers in the 1920s used three-phase model generators rated up to 600 kVA and 2300 volts to represent a power system. General Electric developed model systems using generators rated at 3.75 kVA.[4] It was difficult to keep multiple generators in synchronism, and the size and cost of the units was a constraint. While transmission lines and loads could be accurately scaled down to laboratory representations, rotating machines could not be accurately miniaturized and keep the same dynamic characteristics as full-sized prototypes; the ratio of machine inertia to machine frictional loss did not scale.[5]

## Scale model

A network analyzer system was essentially a scale model of the electrical properties of a specific power system. Generators, transmission lines, and loads were represented by miniature electrical components with scale values in proportion to the modeled system.[6] Model components were interconnected with flexible cords to represent the schematic diagram of the modeled system.

Instead of using miniature rotating machines, accurately calibrated phase-shifting transformers were built to simulate electrical machines. These were all energized by the same source (at local power frequency or from a motor-generator set) and so inherently maintained synchronism. The phase angle and terminal voltage of each simulated generator could be set using rotary scales on each phase-shifting transformer unit. Using the per-unit system allowed values to be conveniently interpreted without additional calculation.

To reduce the size of the model components, the network analyzer often was energized at a higher frequency than the 50 Hz or 60 Hz utility frequency. The operating frequency was chosen to be high enough to allow high-quality inductors and capacitors to be made, and to be compatible with the available indicating instruments, but not so high that stray capacitance would affect results. Many systems used either 440 Hz, or 480 Hz, provided by a motor-generator set, to reduce size of model components. Some systems used 10 kHz, using capacitors and inductors similar to those used in radio electronics.

Model circuits were energized at relatively low voltages to allow for safe measurement with adequate precision. The model base quantities varied by manufacturer and date of design; as amplified indicating instruments became more common, lower base quantities were feasible. Model voltages and currents started off around 200 volts and 0.5 amperes in the MIT analyzer, which still allowed directly driven (but especially sensitive) instruments to be used to measure model parameters. The later machines used as little as 50 volts and 50 mA, used with amplified indicating instruments. By use of the per-unit system, model quantities could be readily transformed into the actual system quantities of voltage, current, power or impedance. A watt measured in the model might correspond to hundreds of kilowatts or megawatts in the modeled system. One hundred volts measured on the model might correspond to one per-unit, which could represent, say, 230,000 volts on a transmission line or 11,000 volts in a distribution system. Typically, results accurate to around 2% of measurement could be obtained.[7] Model components were single-phase devices, but using the symmetrical components method, unbalanced three-phase systems could be studied as well.

A complete network analyzer was a system that filled a large room; one model was described as four bays of equipment, spanning a U-shaped arrangement 26 feet (8 metres) across. Companies such as General Electric and Westinghouse could provide consulting services based on their analyzers; but some large electrical utilities operated their own analyzers. The use of network analyzers allowed quick solutions to difficult calculation problems, and allowed problems to be analyzed that would otherwise be uneconomic to compute using manual calculations. Although expensive to build and operate, network analyzers often repaid their costs in reduced calculation time and expedited project schedules.[8] For example, a stability study might indicate if a transmission line should have larger or differently spaced conductors to preserve stability margin during system faults; potentially saving many miles of cable and thousands of insulators.

Network analyzers did not directly simulate the dynamic effects of load application to machine dynamics (torque angle, and others). Instead, the analyzer would be used to solve dynamic problems in a stepwise fashion, first calculating a load flow, then adjusting the phase angle of the machine in response to its power flow, and re-calculating the power flow.

In use, the system to be modelled would be represented as a single line diagram and all the impedances of lines and machines would be scaled to model values on the analyzer. A plugging diagram would be prepared to show the interconnections to be made between the model elements. The circuit elements would be interconnected by patch cables. The model system would be energized, and measurements taken at the points of interest in the model; these could be scaled up to the values in the full-scale system.[9]

## The MIT network analyzer

The network analyzer installed at Massachusetts Institute of Technology (MIT) grew out of a 1924 thesis project by Hugh H. Spencer and Harold Locke Hazen, investigating a power system modelling concept proposed by Vannevar Bush. Instead of miniature rotating machines, each generator was represented by a transformer with adjustable voltage and phase, all fed from a common source. This eliminated the poor accuracy of models with miniature machines. The 1925 publication of this thesis attracted the attention at General Electric, where Robert Doherty was interested in modelling problems of system stability. He asked Hazen to verify that the model could accurately reproduce the behavior of machines during load changes.

Design and construction was carried out jointly by General Electric and MIT. When first demonstrated in June 1929, the system had eight phase-shifting transformers to represent synchronous machines. Other elements included 100 variable line resistors, 100 variable reactors, 32 fixed capacitors, and 40 adjustable load units. The analyzer was described in a 1930 paper by H.L Hazen, O.R. Schurig and M.F. Gardner. The base quantities for the analyzer were 200 volts, and 0.5 amperes. Sensitive portable thermocouple-type instruments were used for measurement.[10] The analyzer occupied four large panels, arranged in a U-shape, with tables in front of each section to hold measuring instruments. While primarily conceived as an educational tool, the analyzer saw considerable use by outside firms, who would pay to use the device. American Gas and Electric Company, the Tennessee Valley Authority, and many other organizations studied problems on the MIT analyzer in its first decade of operation. In 1940 the system was moved and expanded to handle more complex systems.

By 1953 the MIT analyzer was beginning to fall behind the state of the art. Digital computers were first used on power system problems as early as 'Whirlwind' in 1949. Unlike most of the forty other analyzers in service by that point, the MIT instrument was energized at 60 Hz, not 440 or 480 Hz, making its components large, and expansion to new types of problems difficult. Many utility customers had bought their own network analyzers. The MIT system was dismantled and sold to the Puerto Rico Water Resources Authority in 1954.[11]

## Commercial manufacturers

By 1947, fourteen network analyzers had been built at a total cost of about two million US dollars. General Electric built two full-scale network analyzers for its own work and for services to its clients. Westinghouse built systems for their internal use and provided more than 20 analyzers to utility and university clients. After the Second World War analyzers were known to be in use in France, the UK, Australia, Japan, and the Soviet Union. Later models had improvements such as centralized control of switching, central measurement bays, and chart recorders to automatically provide permanent records of results.

General Electric's Model 307 was a miniaturized AC network analyzer with four generator units and a single electronically amplified metering unit. It was targeted at utility companies to solve problems too large for hand computation but not worth the expense of renting time on a full size analyzer. Like the Iowa State College analyzer, it used a system frequency of 10 kHz instead of 60 Hz or 480 Hz, allowing much smaller radio-style capacitor and inductors to be used to model power system components. The 307 was cataloged from 1957 and had a list of about 20 utility, educational and government customers. In 1959 its list price was \$8,590.[12]

In 1953, the Metropolitan Edison Company and a group of six other electrical companies purchased a new Westinghouse AC network analyzer for installation at the Franklin Institute in Philadelphia. The system, described as the largest ever built, cost \$400,000.[13]

In Japan, network analyzers were installed starting in 1951. The Yokogawa Electric company introduced a model energized at 3980 Hz starting in 1956.[14]

AC Network Analyzers [15]
OwnerYearFrequencyGenerator UnitsTotal circuitsRemarks
MIT19296016209First system in commercial use
Purdue University194244016383Reconstructed after 1929 initial installation
Commonwealth Edison Company19324406186
General Electric Company193748012313
Public Service Electric and Gas Co of New Jersey19384808163
Tennessee Valley Authority193844018270
São Paulo Tramway, Light and Power Company1940440698Brazil
Potomac Electric Power Company19414406120
Public Service Co. of Oklahoma1941607185
Westinghouse Electric Corporation194244022384
Illinois Institute of Technology194544012236Cost \$90,000, sponsored by 17 electrical utilities[16]
Iowa State College194610,000464Continued in commercial use until the early 1970s.
Texas A and M College194744018344Operated until 1971 when it was sold to Lower Colorado Power Authority
City of Los Angeles194744018266
University of Kansas1947608133
Associated Electrical Industries, Ltd.194750012274United Kingdom
Georgia School of Technology194844014322Donated by Georgia Power Corp, cost \$300,000[17]
Pacific Gas and Electric Company194844014324
Consolidated Gas, Electric Light and Power Co. of Baltimore194844016240
United States Bureau of Reclamation194848012240
General Electric Company (No. 2)194948012392
University of California19494806113
Indian Institute of Science194948016338
State Electricity Commission of Victoria195045012--Westinghouse make, in utility service to 1967, 10 kW motor generator input, [18]
Franklin Institute1953440-----Westinghouse make, largest system delivered to that date, cost \$400,000 in 1953 dollars
Cornell University195344018---Decommissioned mid 1960s[19]

## Other applications

### Transient analyzer

A 'transient network analyzer' was an analog model of a transmission system especially adapted to study high-frequency transient surges (such as those due to lightning or switching), instead of AC power frequency currents. Similarly to an AC network analyzer, they represented apparatus and lines with scaled inductances and resistances. A synchronously driven switch repeatedly applied a transient impulse to the model system, and the response at any point could be observed on an oscilloscope or recorded on an oscillograph. Some transient analyzers are still in use for research and education, sometimes combined with digital protective relays or recording instruments.[20]

### Anacom

The Westinghouse Anacom was an AC-energized electrical analog computer system used extensively for problems in mechanical design, structural elements, lubrication oil flow, and various transient problems including those due to lightning surges in electric power transmission systems. The excitation frequency of the computer could be varied. The Westinghouse Anacom constructed in 1948 was used up to the early 1990s for engineering calculations; its original cost was \$500,000. The system was periodically updated and expanded; by the 1980s the Anacom could be run through many simulation cases unattended, under the control of a digital computer that automatically set up initial conditions and recorded the results. Westinghouse built a replica Anacom for Northwestern University, sold an Anacom to ABB, and twenty or thirty similar computers by other makers were used around the world.[9]

### Physics and chemistry

Since the multiple elements of the AC network analyzer formed a powerful analog computer, occasionally problems in physics and chemistry were modeled (by such researchers as Gabriel Kron of General Electric), in the late 1940s prior to the ready availability of general-purpose digital computers.[21] Another application was water flow in water distribution systems. The forces and displacements of a mechanical system could be readily modelled with the voltages and currents of a network analyzer, which allowed easy adjustment of properties such as the stiffness of a spring by, for example, changing the value of a capacitor. [22]

### Structures

The David Taylor Model Basin operated an AC network analyzer from the late 1950s until the mid-1960s. The system was used on problems in ship design. An electrical analog of the structural properties of a proposed ship, shaft, or other structure could be built, and tested for its vibrational modes. Unlike AC analyzers used for power systems work, the exciting frequency was made continuously variable so that mechanical resonance effects could be investigated.

## Decline and obsolescence

Even during the Depression and the Second World War, many network analyzers were constructed because of their great value in solving calculations related to electric power transmission. By the mid 1950s, about thirty analyzers were available in the United States, representing an oversupply. Institutions such as MIT could no longer justify operating analyzers as paying clients barely covered operating expenses. [22]

Once digital computers of adequate performance became available, the solution methods developed on analog network analyzers were migrated to the digital realm, where plugboards, switches and meter pointers were replaced with punch cards and printouts. The same general-purpose digital computer hardware that ran network studies could easily be dual-tasked with business functions such as payroll. Analog network analyzers faded from general use for load-flow and fault studies, although some persisted in transient studies for a while longer. Analog analyzers were dismantled and either sold off to other utilities, donated to engineering schools, or scrapped.

The fate of a few analyzers illustrates the trend. The analyzer purchased by American Electric Power was replaced by digital systems in 1961, and donated to Virginia Tech. The Westinghouse network analyzer purchased by the State Electricity Commission of Victoria, Australia in 1950 was taken out of utility service in 1967 and donated to the Engineering department at Monash University; but by 1985, even instructional use of the analyzer was no longer practical and the system was finally dismantled.[23]

One factor contributing to the obsolescence of analog models was the increasing complexity of interconnected power systems. Even a large analyzer could only represent a few machines, and perhaps a few score lines and busses. Digital computers routinely handled systems with thousands of busses and transmission lines.

## References

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