Pulsed Constant-Current Generators

June 21st, 2011

New Avtech Pulsed Constant-Current Generators

The AV-108E-5A-B and AV-108F-5A-B models are pulsed constant-current generators designed for driving laser diodes and other low impedance loads.

They provide current pulses as high as 12.5 Amperes into load voltages to 90 Volts, pulse widths from 20 us to 1 ms, and average output powers to 40 or 300 Watts. The two new 12.5 Amp models complement the 50 to 200 Amp models in the series.

The high compliance voltage (90V) makes them particularly suitable for driving laser arrays.


The 40 Watt model (the AV-108E-5A-B) is entirely self- contained in a single chassis, and is powered from a standard AC line connection (100-240 Volts, 50-60 Hz). Available to the USA Only

The high-power 300 Watt model (the AV-108F-5A-B) requires an external user-supplied DC power supply in addition to standard AC power. This permits operation at higher duty cycles. Available to the USA Only

Visual Persistence Oscilloscopes

June 15th, 2011

Instek Self-Developed Waveform Image Processing System

GW Instek GDS-3000 Series digital storage oscilloscopes are equipped with a built-in self-developed waveform image processing system which significantly enhances the waveform capture rate. We call this VPO (Visual Persistence Oscilloscope) Technology.

The first generation of analog oscilloscopes utilized fluorescent materials to capture fast electronic signals to generate a dot on a screen. By controlling the intensity and bias of an electron beam, the brightness and tracking of a signal could be generated. This was used to reconstruct a waveform image that would be displayed on a screen for a short time. For this reason, one can observe the details of a signal while the signal is changing with the naked eye.

Digital storage oscilloscopes, usually viewed as 2nd generation oscilloscopes mainly convert analog signals into digital signals through high-speed analog to digital converters (ADC). These signals are then stored in its memory for the CPU to process and draw the waveform. The design of a DSO puts some of its functions far beyond the reach of analog oscilloscopes. For example: waveform storage, math operations (Example: – * / FFT), automatic measurements and pre-triggers. The only reason why analog oscilloscopes still fascinate so many people is because of their ability to display a signal in real-time.

GDS3254 250MHz, 4 Channel , Visual Persistence DSO

GDS3254 250MHz, 4 Channel , Visual Persistence DSO

Conversely, this is also the greatest disadvantage of digital storage oscilloscopes. As the CPU in a DSO does not have the processing power to process a waveform as fast as the signal is changing, only part of the signal is captured and processed. The section of time for when a signal is not captured is called Dead Time. The longer the dead time is, the greater the chance of not detecting a rapid change in the signal. If a DSO cannot detect such signals then it is unable to meet the demands of a modern measurement instrument.

The waveform image processing system designed and developed by GW Instek are mainly used to share the data processing with the CPU, shortening the time needed to draw a waveform and consequently increasing the waveform capture rate.

Furthermore, in order to create a display performance similar to that of analog oscilloscopes, the waveform data for all channels is displayed as a three dimensional image (amplitude, time and intensity). When a strong signal is generated, the waveform will be brighter and the waveform will persist for a longer time, allowing users to easily grasp any instantaneous changes in the waveform. By using an image processing system, waveform data can be quickly acquired by the DSO, processed and displayed on the screen with multiple levels of intensity almost as quickly as an analog oscilloscope.

Instek GDS-3000 Oscilloscope VPO Technology Video

By using VPO technology and a 5 GSa/sec sampling rate, the GDS-3000 Series significantly enhances waveform capture rate, allowing users to clearly observe video signals, DVD signals, and FM signals.

Instek GDS-3354
GDS3354 350MHz, 4 Channel , Visual Persistence Digital Storage Oscilloscope

Instek GDS-3154
GDS3154 150MHz, 4 Channel , Visual Persistence Digital Storage Oscilloscope

New Terahertz Technologies Distribution Agreement

June 14th, 2011

Lake Mary, FL USA – Test Equipment Connection Announces New Terahertz Technologies Distribution Agreement

June 14, 2011 Test Equipment Connection Corporation announced a global distribution agreement to market Terahertz Technologies products.

“Terahertz Technologies advanced line of hand held fiber optic test equipment is tailored for the Photonics and Opto-Electronics user,” said President and COO Mike Novello. “The portable FOTE market is growing rapidly and Terahertz delivers innovative solutions at affordable prices. The FTE-8000 portable optical spectrum analyzer covering the C or L bands and the FTE-7500-Quad OTDR are just two examples of fast, reliable and easy to use Terahertz solutions.”

About Terahertz Technologies

Terahertz TechnologiesTerahertz Technologies has developed a large number of sophisticated instruments for a diverse group of customers in many different industries, ranging from the automotive, fiber optics, communications, photonics, power generation and medical equipment industries and for research laboratories, government entities and educational organizations worldwide. Among these products are optical to electrical converters, electrical to optical converters, fiber optic laser tachometers, fiber optic video links, optical spectrum analyzers, advanced fiber optic loss test sets, optical time-domain reflectometers, fiber optic switches, custom light choppers, laser power and energy meters, laser light sources, and various other optoelectronic products. The principal engineers at Terahertz have over 50 years of combined experience in radiometric and fiber optic instrumentation. Low overhead and efficient designs keep NRE (non-recurring engineering) costs to a minimal level.

About Test Equipment Connection Corporation
Test Equipment Connection Corp., Test Equipment Connection Pte. Ltd., TE Connection Asia Limited, and Test Equipment Connection Europe S.P.R.L. are industry-leading suppliers of new, refurbished and second-hand electronic test and measurement (”T&M”) equipment. The companies sell, buy, lease, rent, trade, repair and calibrate over 400 manufacturers including Anritsu, Rohde & Schwarz, Agilent, Tektronix, Advantest, LeCroy, Chroma, Ophir, AEMC and Fluke, with over 40,000 products available. The companies are a single source supplier with in-house calibration laboratories assuring that customers receive only the highest quality T&M equipment and support. Test Equipment Connection Corporation has over 250,000 customers, a 45,000 square foot warehouse and repair facility in the US, and 18 years of profitability and financial strength.

Visit www.TestEquipmentConnection.com or email sales@testequipmentconnection.com
for more information.

Test Equipment Connection Corporation
30 Skyline Drive
Lake Mary, FL 32746 USA (800) 615-8378

Test Equipment Connection Pte. Ltd.
6 Battery Road
#31-00 Standard Chartered Bank Building
Singapore 049909

TE Connection Asia, Ltd.
Unit E4, 7/F., Phase I, Kaiser Estate,
No. 41 Man Yue Street
Kowloon, Hong Kong

Test Equipment Connection Europe S.P.R.L.
Levels 20, Bastion Tower
5 Place du Champ de Mars
B-1050 Brussels
Belgium


Terahertz
Technologies FTE-7000E-1310

1310nm SM Viper OTDR The TTI FTE-7000 OTDR
is fast, easy to use, affordable and rugged.

Terahertz
Technologies FTE-7000E-1310 Product Page, Data-Sheet, and Ordering


Terahertz
Technologies LTS1500-345

Loss Test Set W/1310/1490/1550nm Triple
Laser Light Source The LTS-1500 greatly simplifies and expedites measurements of
fiber optic links.

Terahertz
Technologies LTS1500-345 Product Page, Data-Sheet, and Ordering


Terahertz
Technologies FTE-7500-147/149/151/153CWDM

1471/1491/1511/1531nm Quad Wavelength CWDM
OTDR/LS with VFL and Broadband Power Meter

Terahertz
Technologies FTE-7500-147/149/151/153CWDM Product Page, Data-Sheet, and Ordering

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Download the PDF Version of this Press Release HERE

Milestone for the future of Wireless Devices

June 13th, 2011

IBM Research scientists announced that they have achieved a milestone in creating a building block for the future of wireless devices.

Yorktown Heights, NY – 10 Jun 2011: Today, IBM Research scientists announced that they have achieved a milestone in creating a building block for the future of wireless devices. In a paper published yesterday in the magazine Science, IBM researchers announced the first integrated circuit fabricated from wafer-size graphene, and demonstrated a broadband frequency mixer operating at frequencies up to 10 gigahertz (10 billion cycles/second).

Designed for wireless communications, this graphene-based analog integrated circuit could improve today’s wireless devices and points to the potential for a new set of appli-cations. At today’s conventional frequencies, cell phone and transceiver signals could be improved, potentially allowing phones to work where they can’t today while, at much higher frequencies, military and medical personnel could see concealed weapons or conduct medical imaging without the same radiation dangers of X-rays.

Graphene, the thinnest electronic material consisting of a single layer of carbon atoms packed in a honeycomb structure, possesses outstanding electrical, optical, mechanical and thermal properties that could make it less expensive and use less energy inside portable electronics like smart phones.

Despite significant scientific progress in the understanding of this novel material and the demonstration of high-performance graphene-based devices, the challenge of integrat-ing graphene transistors with other components on a single chip had not been realized until now, mostly due to poor adhesion of graphene with metals and oxides and the lack of reliable fabrication schemes to yield reproducible devices and circuits.

This new integrated circuit, consisting of a graphene transistor and a pair of inductors compactly integrated on a silicon carbide (SiC) wafer, overcomes these design hurdles by developing wafer-scale fabrication procedures that maintain the quality of graphene and, at the same time, allow for its integration to other components in a complex cir-cuitry.

“Just a few days before IBM commemorates its 100th anniversary, our scientists have achieved a nanotechnology milestone which continues the company’s century-long pur-suit of innovation and technology leadership,” said T.C. Chen, vice president, Science and Technology, IBM Research. “This research breakthrough has the potential to in-crease the performance of communication devices that enable people to interact with greater efficiency.”

The breakthrough is also a major milestone for the Carbon Electronics for RF Applica-tions (CERA) program, funded by DARPA.

How it Works
In this demonstration, graphene is synthesized by thermal annealing of SiC wafers to form uniform graphene layers on the surface of SiC. The fabrication of graphene circuits involves four layers of metal and two layers of oxide to form top-gated graphene transis-tor, on-chip inductors and interconnects.

The circuit operates as a broadband frequency mixer, which produces output signals with mixed frequencies (sum and difference) of the input signals. Mixers are fundamental components of many electronic communication systems. Frequency mixing up to 10 GHz and excellent thermal stability up to 125°C has been demonstrated with the graphene integrated circuit.

The fabrication scheme developed can also be applied to other types of graphene mate-rials, including chemical vapor deposited (CVD) graphene films synthesized on metal films, and are also compatible with optical lithography for reduced cost and throughput.

Previously, the team has demonstrated standalone graphene transistors with a cut-off frequency as high as 100 GHz and 155 GHz for epitaxial and CVD graphene, for a gate length of 240 and 40 nm, respectively.

IBM and Nanotechnology Leadership
In the company’s 100 year history, IBM has invested in scientific research to shape the future of computing. Today’s announcement is a demonstration of the results garnered by IBM’s world-leading scientists and the company’s continual investment in and focus on exploratory research.

Nanotechnology is an enabling technology that is expected to spark advances in various fields. These include advanced functional materials, sensing, tools, healthcare, bio-analytics, water purification, energy technology, and more. IBM scientists apply their nanoscience expertise to problems outside of nanoelectronics and help tackle some of the biggest challenges of our time, such as more efficient use of solar energy, and new ways of purifying or desalinating water.

IBM also recently opened the Binnig and Rohrer Nanotechnology Center – a facility for world-class nanoscale research recently opened on the campus of IBM Research – Zu-rich. The building is the centerpiece of a 10-year strategic partnership in nanoscience between IBM and ETH Zurich, one of Europe’s premier technical universities, where sci-entists will research novel nanoscale structures and devices to advance energy and in-formation technologies. (source www.ibm.com)

Testing RF Devices, Cables Used for Maintenance

June 10th, 2011

Configuration Requirements for Emission Testing and Cables

Question: What are the configuration requirements for emission testing of an Equipment Under Test (EUT) when the cables, which are absent during normal operation and are connected only temporarily (for maintenance, initial installation, pre-programming, repair, adjustment etc..

Answer: ANSI Standard C63.4 – 2003, which is incorporated the FCC Rules by reference (47 CFR 15.31(a)(6) and 15.38), is the procedure the FCC uses for testing most intentional and unintentional radiators. Cables that are used only temporarily for maintenance, repair, adjustment, etc. need not be connected to the EUT during compliance testing. Cables that are used during normal operation, whether permanently connected or not, must be connected. (See Clause 6.2 of ANSI Standard C63.4-2003.)
(source fcc.gov / Publication Number: 368196)


Agilent
85054B
Agilent/HP 85054B Standard Mechanical Calibration Kit, DC to 18 GHz,
Type-N, 50 ohm The Agilent 85054B mechanical calibration kit contains
precision standard devices
Agilent
85052C
Precision mechanical calibration kit, DC to 26.5 GHz, 3.5 mm The Agilent
85052C precision mechanical calibration kit contains precision standard
devices to characterize the systematic errors of Agilent network
analyzers
Agilent
85133E
Agilent/HP 85133E Flexible Cable, 2.4 mm The Agilent 85133E is a 97 cm
(38 in) long flexible cable with a 2.4 mm female2 to PSC-2.4 mm female
connector.
Agilent
85134F
Flexible Cable Set, 2.4 mm to 3.5 mm
Agilent
85133F
Agilent/HP 85133F Flexible Cable Set, 2.4 mm The Agilent 85133F is a 63
cm (25 in) long1 flexible cable set composed of a 2.4 mm female2 to
PSC-2.4 mm
Agilent
85131F
Flexible Cable Set The Agilent 85131F is a 62.2 cm (24.5 in) long1
flexible cable set composed of a 3.5 mm female2 to PSC-3.5 mm female
connector

Test Equipment Connection Now Distributing the New Televes H45

June 7th, 2011

Lake Mary, FL USA – Test Equipment Connection Now Distributing New Televes H45 Field Strength Meters in USA

June 7, 2011 Test Equipment Connection Corporation announced a distribution agreement to market Televes field strength meters in the USA.

“The Televes H45 System Analyzers are affordable but with much more advanced features than regular SLMs.” said President and COO Mike Novello. “This installer tool covers a lot of ground in a single device, and includes a professional-grade spectrum analyzer at a fraction of the cost of a traditional lab unit.”

Some Key Features of the Televes H45 include:

  • Real-Time digital processing (capture time below 10ms)
  • MPEG4 full-HD displaying capability (1080p TV signal on the meter screen)
  • Combo mode with image, spectrum, measurements and quality indicators in one single screen
  • Multi standard tool for CATV, Satellite and off-air signals (QAM A/B/C, DVBS, 8PSK, DSS, DVBS2, NTSC, ATSC/8VSB)
  • Professional-grade spectrum analyzer from 2MHz up to 3.3GHz, with 60dB dynamic range, 300Hz resolution filters and very advanced set of functions (zoom, triggers, tilt, BER on spectrum, min/max, marks, and more)
  • Unique fiber optics interface with built in FO receiver (all the features of the meter available directly from a fiber feed, exactly the same as if you were using the RF input)
  • Complete set of automation features like memories, macros, scans, data logs, and advanced computer suite for data export and job report management.
  • Less than 5lbs of weight, all functionality available from two thumbs with the included capacitive thumbwheel, more than 5 hours of battery life.

About Televes

Televes is focused in the design, development and manufacture of equipment for distributing telecommunication services throughout the infrastructures of buildings and homes. The company is headquartered with manufacturing facilities in Santiago de Compostela Spain. Televes is formed by more than 20 industrial and services subsidiaries, has over 800 employees and holds more than 200 Industrial Property patents. Televes solutions deliver the HD television signal to the digital home environment, with products for the professional installer in charge of certifying the highest levels of quality signals.

About Test Equipment Connection Corporation

Test Equipment Connection Corp., Test Equipment Connection Pte. Ltd., TE Connection Asia Limited, and Test Equipment Connection Europe S.P.R.L. are industry-leading suppliers of new, refurbished and second-hand electronic test and measurement (”T&M”) equipment. The companies sell, buy, lease, rent, trade, repair and calibrate over 400 manufacturers including Anritsu, Rohde & Schwarz, Agilent, Tektronix, Advantest, LeCroy, Chroma, Ophir, AEMC and Fluke, with over 40,000 products available. The companies are a single source supplier with in-house calibration laboratories assuring that customers receive only the highest quality T&M equipment and support. Test Equipment Connection Corporation has over 250,000 customers, a 45,000 square foot warehouse and repair facility in the US, and 18 years of profitability and financial strength.

Visit www.testequipmentconnection.com or email sales@testequipmentconnection.com for more information.

Test Equipment Connection Corporation

30 Skyline Drive
Lake Mary, FL 32746 USA (800) 615-8378 x 141

Test Equipment Connection Pte. Ltd.
6 Battery Road
#31-00 Standard Chartered Bank Building
Singapore 049909

TE Connection Asia, Ltd.
Unit E4, 7/F., Phase I, Kaiser Estate,
No. 41 Man Yue Street
Kowloon, Hong Kong.

Test Equipment Connection Europe S.P.R.L.
Levels 20, Bastion Tower
5 Place du Champ de Mars
B-1050 Brussels
Belgium

Televes H45-599304
Televes H45 Advance Premium System Analyzer with MPEG4, HDMI, Fiber Optics (USA Version)
New

Televes H45-599301
Televes H45 Advance HD System Analyzer with MPEG4, HDMI (USA Version)
New

Televes H45-5993
Televes Field Strength Meters H45 Advance System Analyzer (USA Version)
New

Televes H45 Field Strength Meter Promotional Video

Global Positioning System

May 24th, 2011

What is GPS?

A. GPS consists of three segments – the satellite constellation, ground control network, and user equipment.

The satellite constellation comprises satellites in low earth orbit that provide the ranging signals and navigation data messages to the user equipment. The ground control network tracks and maintains the satellite constellation by monitoring satellite health and signal integrity and maintaining the satellite orbital configuration. Furthermore, the ground control network also updates the satellite clock corrections and ephemerides as well as numerous other parameters essential to determining user position, velocity and time (PVT). The user equipment receives signals from the satellite constellation and computes user PVT. More details on each of the aforementioned GPS segments are provided below.

Video Audio Design UEB400DXP-GPS – Receiver, Recorder and Analyzer for DAB signals The UEB 400 DXP allows the user to receive DAB signals according to ETSI EN300 401

GPS Satellite Constellation:
The baseline satellite constellation consists of 24 satellites positioned in six earth-centered orbital planes with four operation satellites and a spare satellite slot in each orbital plane. The system can support a constellation of up to thirty satellites in orbit. The orbital period of a GPS satellite is one-half of a sidereal day or 11 hours 58 minutes. The orbits are nearly circular and equally spaced about the equator at a 60-degree separation with an inclination of 55 degrees relative to the equator. The orbital radius (i.e. distance from the center of mass of the earth to the satellite) is approximately 26,600 km.

With the baseline satellite constellation, users with a clear view of the sky have a minimum of four satellites in view. It’s more likely that a user would see six to eight satellites. The satellites broadcast ranging signals and navigation data allowing users to measure their pseudoranges in order to estimate their position, velocity and time, in a passive, listen-only mode.

Pendulum Instruments GPS-12RG Rubidium Frequency Standard – GPS-disciplined Rubidium clock for near-Cesium stability Internal battery for increased oscillator stability


Ground Control Network:
At the heart of the Ground Control Network is the Master Control Station (MCS) located at the Schriever (formerly named Falcon) Air Force Base near Colorado Springs , Colorado . The MCS operates the system and provides command and control functions for the satellite constellation.

Aeroflex-IFR GPSG-1000 – GPS/Galileo Portable Positional Simulator. Time-saving portable test set.

The satellites in orbit are continuously tracked from six USAF monitor stations spread around the globe in longitude: Ascension Island , Diego Garcia, Kwajalein , Hawaii , Cape Canaveral and Colorado Springs . The monitor stations form the data collection component of the control network. A monitor station continuously makes pseudorange measurements to each satellite in view. There are two cesium clocks referenced to GPS system time in each monitor station. Pseudorange measurements made to each satellite in view by the monitor station receiver are used to update the master control station’s precise estimate of each satellite’s position in orbit.

User Equipment:
The user equipment, often referred to as “GPS receivers”, captures and processes L-band signals from the satellites in view for the computation of user position, velocity and time. (www.faa.gov)

Are Batteries a Waste of Time and Money?

May 17th, 2011

Batteries are indeed, a waste of money. This means to say that if the power grid was 100% reliable, batteries would not be necessary!

The many worldwide power outages over the past several years make batteries essential as a backup source. Who actually gives batteries a second thought? We simply expect them to work when called upon. Experience has shown that this expectation is pure fiction.

Megger 246002B – Megger 246002B Battery Impedance Tester The instrument measures internal cell impedance and DC terminal voltage

Batteries are extremely important to provide electricity to support many assets and revenue streams during outages. For example, in a generating station, if the turbine suffers an outage, without the back-up battery the turbine lube oil priming pumps would not continuously keep the bearings lubricated causing major damage and lengthy outages. In hospitals, who wants to be in the middle of an operation when an AC outage occurs without proper battery back-up? The applications for batteries are innumerable and frequently unseen. In this world of dependency upon electricity, it is impossible to survive without battery back-up.

Battery Basics

So what makes a battery tick? All batteries, whether rechargeable (secondary) or disposable (primary), use chemical reactions to make electricity. It is necessary to have two dissimilar metallic materials in a current-carrying medium. In lead-acid batteries, the two dissimilar metallic materials are lead and lead oxide in a sulphuric acid medium. Nickel Cadmium batteries use nickel and cadmium compounds in a potassium hydroxide electrolyte medium. Nickel metal hydride batteries (NiMH) are comprised of the same nickel compound as in NiCd cells but the cadmium compound is replaced with a metallic hydride and the liquid electrolyte is replaced with a paste to carry the current. The two types of nickel cells are virtually identical in performance. Even their voltages are the same! Lithium batteries use a lithium-containing oxide or phosphate and carbon. For the purposes of stationary battery testing, this article focuses mainly on lead-acid batteries.

Megger BITE 3 – The Megger BITE3 Battery Impedance Test Equipment determines the health of lead-acid cells up to 2000 Ah

With the importance of batteries established let us consider their chemistry and ways of assessing their health. The age-old habit of testing only the voltage and specific gravity doesn’t work – it never has and never will. The reason for this is that the sum of all of the cells’ voltages must equal the charger output. Voltage (and specific gravity) of lead- acid batteries basically follows the sulphate. If a battery is fully charged, the sulphate will be in the acid and its voltage and specific gravity will be normal (with few exceptions.) If it is in a discharged state, the voltage will be low and since there is at least some sulphate on the plates, the specific gravity will also be low. These tests will therefore reveal the state of charge of the battery, but not its state of health. If the battery has a normal voltage, there is no indication of the health of the battery. When the voltage is abnormal, it may be an indication of a potential problem, but may also be that the battery is merely to some extent discharged.

Nickel cadmium batteries behave somewhat differently than lead-acid batteries. In lead-acid batteries the acid is actually part of the electrochemical process; it reacts with the lead and lead oxide to make electricity. The KOH electrolyte in NiCd batteries is simply a carrier for the current and does not enter the chemical reaction. Therefore, measuring specific gravity of NiCd batteries in service doesn’t indicate anything about the condition of the battery. The one exception is carbonation of the electrolyte. This is caused, over time, by the absorption of carbon dioxide from the air into the KOH and reduces the specific gravity of the electrolyte. If this happens, check with the battery manufacturer. It may simply be a matter of replacing the electrolyte.

Battery Tests

The range of possible tests on a battery ranges from doing nothing (not a good idea) to doing every test possible (still not a good idea). The possible tests include voltage, specific gravity, float current, ripple current, cell temperature, ambient temperature, discharge current and time, intercell connection resistance, capacity (load test), impedance (an internal ohmic test), among others.

Float Voltage

Taking them one at a time, voltage can be one of those misleading tests. Voltage is important, absolutely, and if it is abnormal, then it indicates something about the condition of the battery. If it is normal, it indicates nothing at all about a battery’s condition. This is because voltage is more of an indicator that the charger is functioning properly. The sum of the voltages of all of the batteries in the bank must equal the charger output voltage, resistive losses excluded. A normal voltage is not an indicator of battery capacity, but an abnormal voltage needs further investigation.

Specific Gravity

Specific gravity is similar to voltage as an indicator of battery health. The sulphate is part of the electrochemical reaction. If the battery is discharged, some of the sulphate migrates to the plates and the acid is reduced in specific gravity. If the battery is fully charged, all of the sulphate is in the acid and the specific gravity is normal, say 1,215. There aren’t any studies to validate any correlation between specific gravity and battery capacity. In fact, IEEE 450 has de-emphasised specific gravity to the point of checking only 10% of the batteries each quarter and the full bank annually.

Float Current

In order to keep a battery charged, there is a battle of sorts going on in the battery between its self-discharge and the charger. The battery is always in a state of self-discharge which creates a differential in potential between the battery bank and the charger. This differential in potential causes a small current to flow to keep the battery fully charged. This DC current is called float current.

In flooded lead-acid batteries there is no possibility of thermal runaway because the liquid acid cools the battery through the process of evaporative cooling. However, VRLA batteries do not have extra acid, nor is it in a free liquid form. If the float current increases due to some impending failure or overcharging condition, the temperature increases . The increased temperature allows for more current to flow and further increases the temperature of the battery. A runaway chemical reaction ensues, which can lead to the melting of the battery causing an open circuit. The time from when the float current starts to increase and when thermal runaway might occur is between one and four months. Float current is an important parameter to measure in VRLA batteries.

Ripple Current

Ripple current is a product of the charger which converts AC into DC. No charger has a 100% ripple-free conversion process, which is why filters are frequently added in certain applications. Ripple current generally increases slowly over time as electronic components degrade. If, however, a diode in the rectifier blows, the ripple current can double. As with float current, an increase in ripple current to a point greater than about 5 amps rms for every 100Ah of battery capacity (5%), leads to increased temperature and shortened battery life. Ripple current is another parameter that should be measured periodically.

Temperature

Battery and ambient temperature, although they don’t dictate immediate doom for a battery, can lead to premature failure. For every increase of 10°C in battery temperature above 20°C, the battery life is halved. This means, for example, that a 20 year battery maintained at 35°C instead of the specified 25°C will only last about ten years. In Europe the standard temperature is 20°C and 15 year design life for flooded batteries.

Discharge Current and Time

Discharge current and time is now used more frequently in on-line monitors to aid in determining amp-hours removed and replaced. The value of measuring current and time and calculating Ah removed and replaced is that battery capacity can presumably be calculated. This author believes that there is value in this calculation. The caveat is discussed below under capacity (load) tests.

Intercell Connection Resistance

Intercell connection resistance is one of the tests that needs to be performed, especially if frequent outages occur. It has been said that more than 50% of battery bank failures are due to loose intercell connectors. This is a straightforward test to perform and it can be done in conjunction with impedance testing (discussed below) or as a stand-alone test using a low resistance ohmmeter. Intercell connections come loose due to heating and cooling cycles caused by discharging and recharging as a result of outages. The posts expand and contract and because lead is very malleable will cold flow with each cycle. This is one of the reasons that battery manufacturers tend to recommend tightening bolts to the low end of the torque range so as not to add further stress during cycling.

Capacity

Capacity tests are a necessary evil. If performed properly, they are expensive, time-consuming and have limited predictive value depending upon their frequency. Consider a battery bank that is designed to provide eight hours of back up time. A proper capacity test incorporates a second battery in case of a power outage during the discharge test. This second battery must be at least the same size or bigger than the main battery being tested. The resistive load bank must be connected to the main battery bank and voltage leads are connected to each battery in the bank. This usually takes a full day.

On day 2 the eight hour test begins. A test for intercell connection resistance is often performed before the start of the capacity test. There are two schools of thought about performing the intercell connection resistance test:

1) It is not representative of a true “as found” autonomy test.

2) Certain precautions need to be taken to ensure that no major malfunctions occur that could have been avoided.

If there are major malfunctions, then the bank or at least some of the batteries will need to be replaced in an emergency situation. This decision is for those at each company who write procedures and maintain batteries.

Day 3 is the continuation of the recharge of the main bank. The voltage leads are removed and the resistive load bank is disconnected. The main battery recharge may continue on day 4 if the battery is not yet fully charged and ready for service. A properly run capacity test is the only true method of determining the bank’s actual capacity.

Impedance and Resistance

Impedance, an internal ohmic test, indicates the capability of a cell to deliver current. It is correlated to capacity. Although correlation to capacity is not 100%, it is an excellent way of finding weak batteries in the bank. The EPRI study reveals how well impedance and other internal ohmic tests work in finding weak cells. The impedance test applies and measures an AC current signal and measures simultaneously the AC voltage drop across a battery caused by the AC current signal. Following Ohm’s law, Z = E/i, impedance is calculated. Impedance is inversely proportional to capacity in that as capacity decreases, impedance increases. This test is fast (about 30 minutes for a 60-cell substation battery bank) and is non-invasive.

Data Analysis

What is done with the data collected? How is the data interpreted to ensure that the battery bank will meet the required duty cycle? With the advent of better testing methods such as impedance, more useful data (rather than only voltage and specific gravity) can now be obtained. With such data come the data-handling problems and the analysis to paralysis problems. The recommended method is to use a database to track and trend all battery data over time and dispense with paper forms that cannot compare today’s data with yesterdays. A specialized database, one with space for all measured parameters, is important to aid in determining the condition of batteries and banks.

Entering limits, with which the user is comfortable, in order to gain the most life from a battery without increasing risk, aids tremendously in extracting the most from a battery. The limits should be set for each parameter measured. For example, float voltage limits should follow manufacturers’ guidelines. Internal ohmic test limits are more debatable. In some cases, users will set a “failure limit” of 50% impedance increase for VRLA batteries from a predetermined baseline value. Float current limits tend to be less precise depending upon the size, age and alloy of the battery.

Conclusion

There are many failure modes for batteries. With care and measurement these can be dramatically reduced, especially if little to no testing is presently being performed. The battery is installed, not to add to work load, but to support critical electrical equipment or revenue streams. Proper testing and data analysis can help determine when a battery should be replaced. Testing also helps reduce emergency battery replacements and assists in budgetary planning, thus reducing cost. A properly implemented battery testing regime does not necessarily reduce the work load but it will, most likely, increase reliability of the entire DC network. (Marius Pitzer, Megger)

Phasing Detectors

May 16th, 2011

Megger Phasing Detectors

For use on any grounded electrical system, DETEX Voltage Detectors are available in seven models that cover a range from distribution class to transmission line voltages up to 550 kV. Biddle offers six electronic “beeper” models and one model with LED indication for greater visibility when testing indoors.

The beeper-style electronic detectors provide audible and visual indication of the presence of phase-to-ground ac voltages, in accordance with ANSI C84.1-1982 standards.

The 6.9-kV model is equipped with a telescopic pole. All other models are fitted for universal spline mounting on a hot line pole rated for the voltage of the system being tested.

Electronic voltage detectors for use on distribution line voltages (Cat. No. 514360 series) provide a single red LED.

Detectors rated for transmission line voltages (Cat. No. 514242 series) provide four LEDs for improved visibility at greater distances.

The LED-indicating voltage detector is designed for indoor testing of grounded ac systems. A bright LED indicator provides easy visibility in poor lighting conditions. During testing, the presence of voltages within the detector’s operating range will illuminate the bright LED lamp.

A built-in piezoelectric voltage source provides a test feature to ensure that the detector is operative before use. The self-test is activated by a pushbutton.

The LED detector is equipped with a 48-in. (1219-mm) telescopic pole calibrated and marked for voltages within the ratings of the detector. These demarcations assist the user in adjusting the pole to the length required for safe operation. The pole retracts to 34 in. (864 mm) for convenient storage in a vinyl carrying case when not in use.

Megger 514500-4 Phasing Detector Product Page

Insulation Diagnostics Considered

May 4th, 2011

Diagnostic Insulation Testing Digest

Insulation defects are the most common cause of electrical failure or damage. Regular testing of the quality of the insulation is a decisive part of every maintenance program.

Megger MIT1020-2

Product Highlights Megger Model # 1000-380 Catalog # MIT1020/2 The testers measure to 15 Tera-ohms, thereby making them fully suitable for critical installation tests and establishment of reliable base data for new high-capital equipment.

Only by regular testing can you get the information required to minimize Equipment failure and to plan investments and maintenance programs. Comparing the results of a simple test of the insulation resistance against the limits established for the equipment gives a pass/fail decision. But is a “pass” really a good result? What does fail mean? Where is the problem?

Induced Currents

When we subject a test object to a test voltage, we can measure the induced current and calculate the insulation resistance using Ohm’s law. Unfortunately, the picture is complicated by the fact that the instrument will display a result which is the sum of the following components;

  • Capacitive charging current
  • Absorption- or polarizing current
  • Surface leakage current
  • Leakage current

The capacitive charging current quickly falls to zero, whereas the absorption current falls more slowly as the molecules in the insulation become polarized. After this charging period, just the leakage current and the surface leakage current remain. Understanding these currents and applying some of the following diagnostic techniques which are built into some of Megger’s latest insulation testers allows the operator to better understand the quality of the insulation and identify problems. Each test is designed to offer a different insight into the condition of the insulation. Test voltages no more than 10kV ensure these tests are totally none destructive to insulation, the aim after all is to analyze and diagnose the condition of insulation not over stress it.

Megger MIT400-EN
Insulation and Continuity Tester – The new Megger MIT400 Series insulation and continuity testers has been designed for electrical testing by power utilities, industrial, telecommunication companies, commercial and domestic electricians.

Guard Terminal

Surface leakage current can be diverted round the test instrument measurement circuit using the guard terminal Surface leakage current between the test leads will be present if the insulation is contaminated by dampness, grease or salts. However always check the performance of the Guard terminal when selecting an instrument. Megger provides this important information.

Dielectric Absorption Ratio (DAR)

Good insulation will show increasing resistance during the test as the charging currents disappear. In poor insulation the high leakage currents will hide the charging currents, and a graph of the insulation resistance over time will show a much flatter curve. With certain insulating materials it can take hours for the insulation to become polarized and for the absorption current to fall to zero. How can you make a quick evaluation of the insulation in such situations? Based upon the principle of good insulation showing an increasing insulation resistance test result with time, the DAR is a ratio derived from two results at particular points in time during a test. It has the advantage of being quick, sometimes no more than 60 seconds, and can be seen as independent of temperature. The two time points selected for the DAR test can be defined by the user, and 60seconds/30 seconds is typical. The test is useful in showing up damp or contaminated insulation Because the concept relies on relatively rigid insulating structures, it is however not suitable for use on insulating oils.

Polarization-Index Test (PI)

A popular DAR test is the Polarization-Index Test. Two measurements are taken, at 1 minute and at 10 minutes, and these results are used to calculate a PI ratio.

Step Voltage Test (SV)

Because good insulation is resistive, an increase in test voltage will lead to an increase in current, with the result that the resistance remains constant. A deviation in resistance as voltage increases indicates a problem with the insulation. This test procedure is a good way to locate pinholes and cracks in the insulating material, where ionization occurs and reduces the insulation resistance.

Dielectric Discharge Test (DD)

Bad layers within an insulation are characterized by high absorption currents. If you fully charge the insulation, and then continue to measure in the discharge phase, then within the first few seconds the leakage currents disappear and the capacitance is discharged, leaving just the absorption current for the test instrument to measure. If a layer of insulation is defect, it would be expected to show reduced leakage resistance, but the same capacitance. The DD is a value calculated from the current, capacitance and test voltage, and can indicate problems in individual layers of the insulation.

Burn Mode

To locate a fault it can sometimes be beneficial to create and maintain an arc at the fault so that the ionization can be detected.

Temperature and Humidity

Temperature changes can have a significant effect on the insulation resistance measurement. A 10-degree rise in temperature halves the resistance. This effect can be quantified, and temperature correction tables can be used to help evaluate test results. Humidity effects are unfortunately not so easy to quantify, as different insulating materials absorb moisture to different extents, which can also be dependent upon the age and condition of the equipment. An attempt should however be made to account for the effect of humidity on the test result.

Measure Current or Resistance?

Insulation testers measure current and calculate the resistance. One of the reasons for this is probably just that it is traditional. Good insulation gives a high resistance value, poor insulation gives low results. Furthermore, good insulation is resistive; increasing the test voltage increases the current, but the resistance should stay the same. Some faults are however easier to identify by observing the change in current. Many insulation testers give you the choice of seeing the result in either resistance or current.