To detect problems, the professional “listens” in many ways: With eyes and ears, to see and hear conditions that may indicate problems

• With thermometers and thermal imagers, to detect overheating, poor electrical connections or failing bearings
• With digital multimeters and power analyzers, to diagnose electrical problems
• Using techniques like lubricant analysis, to gauge machine condition over time

And now the maintenance professional has a valuable new way not just to listen, but to find mechanical problems and fixes: the Fluke 810 Vibration Tester. It’s a unique new kind of troubleshooting tool, engineered to detect and evaluate machine vibration immediately and recommend any needed repairs.

A new kind of troubleshooting tool

Many industrial maintenance teams today work under severe restrictions on money and time. They may not have the resources to train for and implement the typical long-term vibration analysis program. The Fluke 810 is designed specifically for maintenance professionals who need to troubleshoot mechanical problems and quickly understand the root cause of equipment condition.

The handheld Fluke 810 is designed and programmed to diagnose the most common mechanical problems of unbalance, looseness, misalignment and bearing failures in a wide variety of mechanical equipment, including motors, fans, blowers, belts and chain drives, gearboxes, couplings, pumps, compressors, closed coupled machines and spindles.

Many professionals may think there are only two options for vibration testing; high end vibration analyzers that are expensive and difficult to use, and low-end vibration pens which aren’t particularly accurate. The Fluke 810 fills the middle of this category as it combines the diagnostic capability of a trained vibration analyzer with the speed and convenience of lower-end testers, at a reasonable price. It is a new type of test tool for vibration testing.

The Fluke 810 is not merely a vibration detector, but a complete diagnostic and problem-solving solution. The diagnostic technology in the Fluke 810 analyzes machinery condition and identifies faults by comparing vibration data to an extensive set of rules and algorithms developed over years of field experience. The Fluke 810 determines fault severity using a unique technology to simulate a fault-free condition and establish a baseline for instant comparison to gathered data. This means that every measurement taken is compared to a “like new” machine.

Not just data, but actionable results

When it detects a fault, the Fluke 810 identifies the problem, the location and severity on a four-level scale to help the maintenance professional prioritize maintenance tasks. It also recommends repairs. Context-sensitive on-board help provides new users with real-time guidance and tips.

Mechanical diagnosis with the Fluke 810 begins when the user places the Fluke tri-axial TEDS accelerometer on the machine under test. The accelerometer has a magnetic mount and can also be installed by attaching a mounting pad using adhesive. A quick-disconnect cable connects the accelerometer to the Fluke 810 tester. As the machine under test operates, the accelerometer detects its vibration along three plans of movement (vertical, horizontal and axial) and transmits that information to the Fluke 810. Using a set of advanced algorithms, the 810 vibration tester then provides a plain-text diagnosis of the machine with a recommended solution.

No training? No problem

Mechanical equipment is typically evaluated by comparing its condition over time to an established baseline condition. Vibration analyzers used in condition-based monitoring programs rely upon these baseline conditions to evaluate machine condition and estimate remaining operating life. System operators must have considerable training and experience before they can determine the meaning and significance of the vibration spectra they detect.

But what about the maintenance pro who isnt trained in vibration analysis? How do you tell the difference between acceptable vibration, and the kind of vibration that demands immediate attention to service or replace troubled equipment?

The Fluke 810 provides the answer. Extensive experience with mechanical vibration, what it means and how to fix it is built into the advanced algorithms of the Fluke 810. Now the maintenance professional can quickly and reliably determine the cause of the machine vibration, learn the severity and location of the problem and receive recommendations for repair. It’s all done with the intelligence built into the tester, without the extensive training, monitoring and recording required for typical vibration monitoring programs.

The Fluke 810 delivers plain language recommendations about what to do next. For equipment maintenance teams hard pressed and on the go, these precise directions re what they need to take action now, maintain mechanical equipment in top shape, and keep facilities productive.

Global Test Supply is a distributor of Fluke test equipment. For more information on the Fluke 810 vibration tester or to have any questions answered on your test equipment needs visit Global Test Supply or call 888-610-7664.

Not only will you own one of the world’s best thermal imaging cameras, qualified customers are eligible to receive a FREE 8GB Apple iPod Touch, subject to the terms and conditions of this special, limited offer. For more information, contact Global Test Supply today!

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Improving upon the popular Fluke 62, the Fluke 62 MAX and 62 MAX+ are ergonomically designed for a more natural hand fit. Rugged and accurate, both models are IP54 rated for dust and water resistance. Each model is small and lightweight, so it can easily clip onto your belt loop or fit easily in your tool box. The 62 MAX and MAX+ are the only infrared thermometers that can survive a 9.8 foot drop, making them the only IR thermometers that you can handle without care!

The Fluke 62 MAX single laser IR thermometer features a 10:1 optical resolution and a 10 hour battery life. The Fluke 62 MAX+ features dual rotating lasers and a 12:1 optical resolution, and has an 8 hour battery life. Other features for both models include a large easy-to-read screen, backlit display, and Hi and Lo alarms for rapid display of measurements outside the limits. Each model is powered by a single, standard AA battery. For full specs and pricing, contact Global Test Supply today!

The Fluke 805 provides a more complete picture by measuring variables such as bearing condition and temperature as well as overall vibration. The meter compensates for user variance such as force or angle with its combination vibration and force sensor tip, yielding accurate and repeatable readings. The Fluke 805 also features a four level scale that indicates the severity of problems for overall vibration and bearing condition.

A stand out feature of the Fluke 805 is its sensor sensitivity, allowing you to cover most machine and component types with one meter. Easily test overall vibration from 10 Hz to 1,000 Hz, and bearing condition from 4,000 Hz to 20,000 Hz. Testing is enhanced by the straight-forward user interface that minimizes user input to RPM range and equipment type. The Fluke 805 also has data management capabilities for matching existing equipment IDs and exporting to Microsoft Excel, allowing for trending over time.

Other features include a large high resolution screen, on board memory that holds up to 3,500 measurements, and a flashlight for viewing measurement locations in dark areas. For full specs and pricing, contact Global Test Supply today!

SR Safety Training Engineer at AVO Training Institute

Most of us have grown up with an understanding that high short circuits currents are detrimental. We have gone to a lot of efforts to reduce the level of short circuit currents wherever possible. We have invented current limiting fuses and other current limiting devices. We have intentionally placed impedance in the circuit to limit the amount of current available. The focus has been primarily on equipment preservation and continuous operation. For most of our lifetimes when you asked a utility to give you the short circuit availability they would give you the value considering only the impedance of the transformer. After all, it is worst case (highest current). It will be higher than including the impedance of the entire system (infinite bus).

That philosophy has served us well for the stated objectives. Personnel safety, however, requires a fresh look at this philosophy. When an arc flash event occurs workers are subjected to multiple hazards, one of which is burns. The calculated energy that produces the burn is known as incident energy and is expressed in calories/cm2 or joules/cm 2. The severity of burning as with all burns is a product of the heat generated and the exposure time to the heat. The duration of the heat energy in an electrical system is determined by the speed of the protective device that clears the short circuit or by other factors in the event of a device failure. Electrical protective devices operate on an inverse time-current relationship. See figure 1. Simply stated the device operates faster at higher current and slower at lower current.

Figure 1 is representative of a relay operating curve. The red lines indicate an operating time of 0.1 seconds at a current of 30,000 amperes and the green lines indicate an operating time of 1 second at 9,000 amperes. This inverse relationship is the same whether it is a fuse, a breaker, or a relay.

The time to clear the fault is further complicated because the current is passing through the air which has a higher resistance than the conductors and results in a lower current magnitude and a corresponding increase in clearing time of the protective device. Whether the longer exposure period has a higher impact than a higher current depends on the characteristics of the system. In my experience, most of the time, the longer clearing time is more critical than the higher short circuit current.

Consider the following case study:

A manufacturing facility was served by a transformer with an impedance of 1.5% which had standard over-current protection. The owner and the consulting engineer determined to replace the transformer with a 5.75% impedance transformer, with under-oil current limiting fuses in the primary of the transformer and cable limiters on the secondary cables. The resultant arcing current was below the current-limiting range of the limiting devices when buses were faulted downstream. The downstream incident energy rose from 5.9 cal/cm2 to 43.33 cal/cm2 (IEEE 1584 calculation). The situation changed from being very manageable with PPE protection to one which requires some further mitigation to reduce arc flash energy.

In conclusion, as we analyze and design electrical distribution systems it is necessary to study the harmful effects of both maximum short circuit currents (bolted faults) and lower impedance arcing short circuit currents.

Thermography and Infrared Light

Infrared light or thermography is the use of an infrared imaging and measurement camera to “see” and “measure” thermal energy emitted from an object. Thermal, or infrared energy, is light that is not visible because its wavelength is too long to be detected by the human eye; it’s the part of the electromagnetic spectrum that we perceive as heat. Unlike visible light, in the infrared world, everything with a temperature above absolute zero emits heat. Even very cold objects, like ice cubes, emit infrared.

Infrared Imaging

The higher the object’s temperature, the greater the IR radiation emitted. Infrared allows use to see what our eyes cannot. Infrared thermography cameras produce images of invisible infrared or “heat” radiation and provide precise non-contact temperature measurement capabilities. Nearly everything gets hot before it fails, making infrared cameras extremely cost-effective, valuable diagnostic tools in many diverse applications. And as industry strives to improve manufacturing efficiencies, manage energy, improve product quality, and enhance worker safety, new applications for infrared cameras continually emerge.

HOW DOES AN IR CAMERA WORK?

Infrared Energy Detection

An infrared camera is a non-contact device that detects infrared energy (heat) and converts it into an electronic signal, which is then processed to produce a thermal image on a video monitor and perform temperature calculations. Heat sensed by an infrared camera can be very precisely quantified, or measured, allowing you to not only monitor thermal performance, but also identify and evaluate the relative severity of heat-related problems.

Recent Infrared Innovations

Recent innovations, particularly detector technology, the incorporation of built-in visual imaging, automatic functionality, and infrared software development, deliver more cost-effective thermal analysis solutions than ever before.

WHY MEASURE TEMPERATURE?

Infrared and Temperature Measurement

Finding a problem with an infrared camera is sometimes not enough. In fact, an infrared camera image alone without accurate temperature measurements says very little about the condition of an electrical connection or worn mechanical part. Many electrical targets are operating properly at temperatures that are significantly above ambient. An infrared image without measurement can be misleading because it may visually suggest a problem that does not exist.

Predictive Maintenance

Infrared cameras that incorporate temperature measurement allow predictive maintenance professionals to make well informed judgements about the operating condition of electrical and mechanical targets. Temperature measurements can be compared with historical operating temperatures, or with infrared readings of similar equipment at the same time, to determine if a significant temperature rise will comprise component reliability or plant safety.

Digital Image Storage

Digital image storage, available on most FLIR infrared cameras, produces calibrated thermal images that contain over 78,000 independent temperature measurements that can be measured at any time.

WHY USE INFRARED?

A picture says a thousand words; infrared technology is the only diagnostic technology that lets you instantly visualize and verify thermal performance. FLIR’s infrared cameras show you thermal problems, quantify them with precise non-contact temperature measurement, and document them automatically in seconds with professional easy-to-create IR reports.

Infrared for Predictive Maintenance

Nearly everything that uses or transmits power gets hot before it fails. Cost effective power management is critical to maintaining the reliability of your electrical and mechanical systems. And today, no one would argue that infrared thermography is one of the most effective proven predictive maintenance (PM) technology available to quickly, accurately and safely locate problems prior to failure. Finding and fixing a poor electrical connection before a component fails can save you the much greater costs associated with manufacturing downtime, production losses, power outages, fires and catastrophic failures.

Infrared Cameras and Software that Work Together

But using infrared images to find a problem is sometimes not enough. In fact, an infrared camera image without an accurate measurement says very little  about the condition of an electrical connection or worn mechanical part. And, an IR survey without a simple, fast way to report and analyze inspection results provides no ability to make timely repair decision or locate and separate those ‘hot spots’ that can cause problems from those associated with equipment operating normally.

FLIR’s infrared cameras and software not only quickly locate problems, their non-contact precision temperature measurement and analysis capabilities instantly deliver the answers you need to understand what repair action to take, and when.

An Infrared Camera Just for You

Whether you’re looking at buildings or hybrid circuits, there’s a FLIR infrared camera right for your application. With a complete line of infrared cameras, software, accessories, world-class thermographic training and application support, FLIR stands ready to meet your specific infrared needs. FLIR is the one IR company you can specify and justify with confidence. Make sure that all the reliability you planned for gets delivered to your customer.

Global Test Supply is a distributor of FLIR Thermal Imaging Cameras. We have cameras for sell or rent. Give us a call today to talk to a sales technician about your thermal imaging needs.

The issues that determine what method is best for a given coating measurement include the type of coating, the substrate material, the thickness range of the coating, the size and shape of the part, and the cost of the equipment. Commonly used measuring techniques for cured organic films include nondestructive dry film methods such as magnetic, eddy current, ultrasonic, or micrometer measurement and also destructive dry film methods such as cross-sectioning or gravimetric (mass) measurement. Methods are also available for powder and liquid coatings to measure the film before it is cured.

Magnetic Film Thickness Gauges

Magnetic film gauges are used to non destructively measure the thickness of a nonmagnetic coating on ferrous substrates. Most coatings on steel and iron are measured this way. Magnetic gauges use one of two principles of operation: magnetic pull-off or magnetic/electromagnetic induction.

Magnetic Pull-off

Magnetic pull-off gauges use a permanent magnet, a calibrated spring, and a graduated scale. The attraction between the magnet and magnetic steel pulls the two together. As the coating thickness separating the two increases, it becomes easier to pull the magnet away. Coating thickness is determined by measuring this pull-off force. Thinner coatings  will have stronger magnetic attraction while thicker films will have comparatively less magnetic attraction. Testing with magnetic gauges is sensitive to surface roughness, curvature, substrate thickness, and the make up of the metal alloy.

Magnetic pull-off gages are rugged, simple, inexpensive, portable, and usually do not require any calibration adjustment. They are a good, low-cost alternative in situations where quality goals require only a few readings during production.

Pull-off gauges are typically pencil-type or rollback dial models. Pencil-type models (PosiPen shown in Fig 1) use a magnet that is mounted to a helical spring that works perpendicularly to the coated surface. Most pencil-type pull-off gauges have large magnets and are designed to work in only one or two positions, which partially compensate for gravity. A more accurate version is available, which has a tiny, precise magnet to measure on small, hot, or hard-to-reach surfaces. A triple indicator ensures accurate measurements when the gauge is pointed down, up, or horizontally with a tolerance of ±10%.

Fig 1 – Pencil-type magnetic pull-off thickness gauge

Rollback dial models (PosiTest shown in Fig 2) are the most common form of magnetic pull-off gauge. A magnet is attached to one end of a pivoting balanced arm and connected to a calibrated hairspring. By rotating the dial with a finger, the spring increases the force on the magnet an pulls it from the surface. These gauges are easy to use and have  balanced arm that allows them to work in any position, independent of gravity. They are safe in explosive environments and are commonly used by painting contractors and small powder coating operations. Typical tolerance is ±5%.

Fig 2 – Roll-back dial magnetic pull-off thickness gauge

Magnetic and Electromagnetic Induction

Magnetic induction instruments use a permanent magnet as the source of the magnetic field. A Hall-effect generator or magneto-resistor is used to sense the magnetic flux density at a pole of the magnet. Electromagnetic induction instruments use an alternating magnetic field. A soft, ferromagnetic rod wound with a coil of fine wire is used to produce a magnetic field. A second coil of wire is used to detect changes in magnetic flux.

These electronic instruments measure the change in magnetic flux density at the surface of a magnetic probe as it nears a steel surface. The magnitude of the flux density at the probe surface is directly related to the distance from the steel substrate. By measuring flux density the coating thickness can be determined.

Fig 3 – Electronic magnetic induction thickness gauges

Electronic magnetic gauges (e.g. PosiTector 6000 F Series, PosiTest DFT Ferrous) come in many shapes and sizes. They commonly use a constant pressure probe to provide consistent readings that are not influenced by different operators. Readings are shown on a liquid crystal display (LCD). They can have options to store measurement results, perform instant analysis of readings, and output results to a printer or computer for further examination. Typical tolerance is ±1%.

The manufacturer’s instructions should be carefully followed for most accurate results. Standard test methods are available in ASTM D 1186, D 7091-05, ISO 2178 and ISO 2808.

Eddy Current

Eddy current techniques are used to non destructively measure the thickness of non conductive coatings on nonferrous metal substrates. A coil of fine wire conducting a high-frequency alternating current (above 1 MHz) is used to set up an alternating magnetic field at the surface of the instrument’s probe. When the probe is brought near a conductive surface, the alternating magnetic field will set up eddy currents on the surface. The substrate characteristics and the distance of the probe from the substrate (the coating thickness) affect the magnitude of the eddy currents. The eddy currents create their own opposing electromagnetic field that can be sensed by the exciting coil or by a second, adjacent coil.

Eddy current coating thickness gauges (e.g. PosiTector 6000 N Series) look and operate like electronic magnetic gauges. They are used to measure coating thickness over all nonferrous metals. Like magnetic electronic gauges, they commonly use a constant pressure probe and display results on an LCD. They can also have options to store measurement results or perform instant analysis of readings and output to a printer or computer for further examination. The typical tolerance is ±1%. Testing is sensitive to surface roughness, curvature, substrate thickness, type of metal substrate and distance from an edge.

Standard methods for the application and performance of this test are available in ASTM B 244, ASTM D 1400, D 7091-05 and ISO 2360.

It is now common for gauges to incorporate both magnetic and eddy current principles into one unit (e.g. PosiTector 6000 FN, PosiTest DFT Combo). Some simplify the task of measuring most coatings over any metal by switching automatically from one principle of operation to the other, depending upon the substrate. These combination units are popular with painters and powder coaters.

Ultrasonic

The ultrasonic pulse-echo technique of ultrasonic gauges (e.g. PosiTector 200) is used to measure the thickness of coatings on nonmetal substrates (plastic, wood, etc.) without damaging the coating.

Fig 4 – Ultrasonic gauge can measure the thickness of coatings on nonmetallic substrates

The probe of the instrument contains an ultrasonic transducer that sends a pulse through the coating. The pulse reflects back from the substrate to the transducer and is converted into a high frequency electrical signal. The echo waveform is digitized and analyzed to determine coating thickness. In some circumstances, individual layers in a multi-layer system can be measured.

Typical tolerance for this device is ±3%. Standard methods for the application and performance of this test are available in ASTM D 6132.

Micrometer

Micrometers are sometimes used to check coating thickness. They have the advantage of measuring any coating/substrate combination but the disadvantage of requiring access to the bare substrate. The requirement to touch both the surface of the coating and the underside of the substrate can be limiting and they are often not sensitive enough to measure thin coatings.

Two measurements must be taken: one with the coating in place and the other without. The difference between the two readings, the height variation, is taken to be the coating thickness. On rough surfaces, micrometers measure coating thickness above the highest peak.

Destructive Tests

One destructive technique is to cut the coated part in a cross section and measure the film thickness by viewing the cut microscopically. Another cross sectioning technique uses a scaled microscope to view a geometric incision through the dry-film coating. A special cutting tool is used to make a small, precise V-groove through the coating and into the substrate. Gauges are available that come complete with cutting tips and illuminated scaled magnifier.

While the principles of this destructive method are easy to understand, there are opportunities for measuring error. It takes skill to prepare the sample and interpret the results. Adjusting the measurement reticule to a jagged or indistinct interface may create inaccuracy, particularly between different operators. This method is used when inexpensive, nondestructive methods are not possible, or as a way of confirming nondestructive results. ASTM D 4138 outlines a standard method for this measurement system.

Gravimetric

By measuring the mass and area of the coating, thickness can be determined. The simplest method is to weigh the part before and after coating. Once the mass and area have been determined, the thickness is calculated using the following equation:

T = m x 10
A x d

where T is the thickness in micrometers, m is the mass of the coating in milligrams, A is the area tested in square centimeters, and d is the density in grams per cubic centimeter.

It is difficult to relate the mass of the coating to thickness when the substrate is rough or the coating uneven. Laboratories are best equipped to handle this time-consuming and often destructive method.

Measurement Before Cure

Wet-film thickness gauges help determine how much material to apply wet to achieve a specified dry-film thickness provided that the percent of solids by volume is known. They measure all types of wet organic coatings, such as paint, varnish, and lacquer on flat or curved smooth surfaces.

Measuring wet film thickness during application identifies the need for immediate correction and adjustment by the applicator. Correction of the film after it has dried or chemically cured requires costly extra labor time, may lead to contamination of the film, and may introduce problems of adhesion and integrity of the coating system.

The equations for determining the correct wet-film thickness (WFT), both with and without thinner, are as follows:

Without thinner:

WFT = desired dry film thickness
% of solids by volume

With thinner:

WFT = desired dry film thickness  /  % of solids by volume
100%   +   % of thinner added

Wet-film is most often measured with a wet film comb or wheel. The wet-film comb is a flat aluminum, plastic, or stainless steel plate with calibrated notches on the edge of each face. The gauge is placed squarely and firmly onto the surface to be measured immediately after coating application and then removed. The wet-film thickness lies between the highest coated notch and the next uncoated notch. Notched gauge measurements are neither accurate nor sensitive, but they are useful in determining approximate wet-film thickness of coatings on articles where size and shape prohibit the use of more precise methods. (ASTM D1212).

The gauge should be used on smooth surfaces, free from irregularities and should be used along the length, not the width, of curved surfaces. Using a wet-film gauge on quick-drying coatings will yield inaccurate measurements. ASTM D4414 outlines a standard method for measurement of wet-film thickness by notch gauges.

A wet film wheel (eccentric roller) uses three disks. The gauge is rolled in the wet film until the center disk touches the wet film. The point where it makes contact provides the wet film thickness.

Powder coatings can be measured prior to curing with a simple hand-held comb or an ultrasonic gauge. The uncured powder film comb works much the same way as wet film gauge. The comb is dragged through the powder film and the thickness lies between the highest numbered tooth which made a mark and has powder clinging to it, and the next highest tooth which left no mark and has no powder clinging to it. These gauges are relatively inexpensive with accuracy of ±5mm. They are only suitable as a guide since the cured film may be different after flow. Marks left by the gauge may affect the characteristics of the cured film.

An ultrasonic device can be used non-destructively on uncured powder on smooth metallic surfaces to predict the thickness of the cured film. The probe is positioned a short distance from the surface to be measured and a reading is displayed on the LCD of the device. Measurement uncertainty is ±5mm.

About the Author

David Beamish is the general manager of Defelsko Corporation, a New-York based manufacturer of hand-held coating test instruments sold worldwide. He has a degree in Civil Engineering and has more than 17 years experience in the design, manufacture, and marketing of these testing instruments in a variety of international industries including industrial painting, quality inspection, and manufacturing. He conducts training seminars and is an active member of various organizations including NACE, SSPC, ASTM and ISO.

You can find a full product range of Defelsko Thickness Gauges on GlobalTestSupply.com.

Ampere – a unit of measure for the rate of current flow.

Apparent power – applied voltage multiplied by current in an AC circuit. This value would not take the power factor into account. Unit is voltamperes (VA).

Balanced load – AC power system using more than two wires, where the current and voltage are of equal value in each energized conductor.

Bandwidth – the range of frequencies over which an instrument provides accurate measurement.

Billing consumption – total amount of energy consumed during a predetermined period (usually 28 to 33 days)

Consumption (active energy) – actual electrical energy used measured in kilowatthours (kWh) by the watthour meter, regardless of the power factor.

Crest factor – the ratio of the peak value of a waveform (voltage or current) to the RMS value.

Current transformer – an instrument accessory which detect current flow without breaking the circuit under test. An AC transformer, usually step-down; typical ratio would be 1000:1. This would indicate 1000A on the primary and 1A on the secondary.

Current transformer ratio – the ratio of primary amperes divided by secondary amperes.

Delta Connection – a circuit formed by connecting three electrical devices in series to form a closed loop; most often used in three-phase connections.

Demand (active, real, or true power) – the power which is actually consumed by the load. This measurement takes the power factor into account.

Demand interval (integration period) – the period of time over which the energy is averaged. Typical demand intervals are 15, 30, or 60 minutes.

Derating Factor – a number defined as 1.414 x  average RMS phase current/peak phase current. This factor, when applied to the rated load of a transformer, gives an indication as to the percent loading that is reasonable when that transformer must service nonlinear loads.

Displacement Power Factor – the difference between apparent power and true power when only the phase relationship of voltage and current at the fundamental are taken into account.

Distortion Factor (%DF) – Total harmonic distortion referenced to the total RMS signal (THD-R).

Distortion Power Factor – the difference between apparent power and true power at all harmonic frequencies.

Frequency – the number of complete cycles of AC voltage which occurs during one second (Hz).

Harmonics – current or voltages which have frequencies that are integer multiples of the fundamental power frequency; common and some times dangerous in nonlinear loads.

Heating effect – temperature increase in electrical distribution equipment caused by an increase in RMS current.

Impedance – the total opposition to alternating current flow in an electrical circuit (Z).

Inductive Reactance – the force which acts as a resistance in an inductor to limit the flow of current. This force creates a leading power factor in AC circuits.

Initiator pulses – electrical impulses generated from utitliy revenue meters. Each pulse indicates a specific number of watts consumed. These pluses are used within energy analyzers to measure energy consumption and demand.

K factor – a number based on the harmonic content of load current that determines the maximum safe loading on a power source.

K-rated transformers – a transformer that is rated or designed to serve as the source for a predefined capacity of harmonic current.

Peak demand (maximum RMS power) – the highest average load during a specified time interval (kW).

Phase – time relationship between current and voltage in AC circuits.

Potential transformer – an instrument transformer used to step down high voltage potentials to lower levels acceptable for the input of electrical test instruments.

Power factor – the ratio of true power (watts) to apparent power (voltamperes). Expressed in decimal form.

Ratchet demand – determining the billing demand based upon a pre-established peak average demand (usually at 75%, 80%, or 100% of the pre-established peak).

Reactance – the opposition to current flow in an AC circuit introduced through inductance or capacitance.

Reactive compensation power – the reactive power to be applied to an AC network for power factor correction; adding capacitance in order to bring the voltage and current waveform in phase.

Reactive power (kvar) – power which is actually “borrowed” from the load and returned to the power source each cycle; unused power.

Resolution – the smallest unit value that an instrument can measure

Resonance – when the inductance in the system and the natural capacitance of the system, or added capacitors, form a tuned circuit resonant at one or more of the harmonic frequencies produced by nonlinear loads.

RS-232 – a computer interface connector used to connect serial devices such as instruments for information transfer.

Sensitivity – the smallest input that will provide a specified output.

Skin effect – phenomenon in which high harmonic frequencies cause electrons to flow to the outer sides of a conductor, reducing its cross-sectional diameter, ad hence its ampacity rating.

Sliding demand – calculating average demand by averaging the average demand over several successive time intervals, advancing one interval at a time.

THD (%THD, Total Harmonic Distortion) – the contribution of all harmonic frequency currents or voltages to the fundamental current or voltage, expressed as a percentage of the fundamental.

THDF (Transformer Harmonic Derating Factor) – method of calculating transformer derating established by CBEMA for phase-to-neutral loads.

True RMS – capability to accurately measure the value of AC voltage and current having a nonsinusoidal waveform as well as sinusoidal waveforms.

Unbalanced load – an AC power system using more than two wires, where the current is not equal in the current-carrying wires due to an uneven loading of the phases.

Watt – the measure of real power. It is the power expended when one ampere of direct current flows through a resistance of one ohm.

Wye connection – a connection of three components made in such as manner that one end of each component is connected; generally used to connect devices to  a three-phase power system.

As with many serial data systems, both ARINC 429 and MIL-STD-1553 are differential busses. ARINC 429 is the simpler and less costly of the two. The physical connection is via twisted pair wires with balanced differential signals. It uses a self clocking, self synchronizing data bus. MIL-STD-1553 uses dual redundant balanced differential pairs. The peak to peak voltage allowed in the differential pair of an ARINC 429 system is 10 volts whereas the peak to peak output voltage of a transmitter on the MIL-STD-1553 bus is allowed to be as high as 18-27 volts. Both systems are designed for noise immunity and signal integrity. Among the plethora
of modern serial data standards, both avionics busses are fairly low speed compared to PCI-Express, SAS or other standards which transport large amounts of data over short distances inside personal computers.

Capturing and Viewing Signals

Since the edge rates of signals and the command/data transmission rate of the busses is moderate, an engineer working on a system using ARINC 429 or MIL-STD-1553 does not need the type of very expensive oscilloscope used to capture signals sent on multi gigabit per second busses. The WaveSurfer and WaveRunner classes of oscilloscopes from LeCroy are well matched to this application. The images used in this paper to illustrate capturing, viewing, decoding and troubleshooting signals were gathered using those types of oscilloscopes. Figure 1 shows a typical example of serial data decoding. Though this particular image shows MIL-STD-1553, the decoding of many types of serial data looks very similar. Rather than the engineer spending a large amount of time peering at the shape of a serial data signal on his oscilloscope screen, counting highs/lows and decoding the data in his head the oscilloscope can highlight different portions of the signal content with different background colors, digitally decode the data and display the resulting digital interpretation along with the analog shape of the electrical waveform from the bus. This not only saves the engineer considerable time in developing a new product (or trouble shooting a problem), it also greatly reduces the chance of human error in “eyeball interpretation” of the signal shape. Note that in Figure 1 the upper trace is at longer time/division. It shows more signal length, but with less detail than the lower trace, which is a zoom of the upper trace.

Figure 1: A MIL-STD-1553 signal is viewed and decoded on the upper trace. The lower trace shows a zoomed portion of the upper signal. Note the zoom has a more detailed level of decoding.

In addition to seeing the voltage vs time trace in more detail in the zoom view, the oscilloscope also shows more details of the decoding of the signal. This type of zooming to get more detail is particularly useful in modern digital oscilloscopes which have long data acquisition memory lengths and hence have the ability to capture more signal details than will conveniently fit onto the pixels of a typical flat panel display.

Using the Decoded Signal

Sometimes the engineer can get all the information he needs to confirm proper operation of a circuit or device by viewing the decoded signal. But more often the engineer needs to examine a long signal acquisition or even many acquisitions in order to spot problems or to characterize correct device operation. Figure 2 is an example of the view and decode of an ARINC 429 signal. It is somewhat similar to Figure 1; the upper trace shows one second of signal shape ( 10 divisions of the oscilloscope screen at 100 msec/div) and the lower trace is a zoom detail of that data. As with Figure 1 the zoom trace shows more detail of the voltage vs time trace and also more detail of the decoding of the data. There is a further feature at the bottom of Figure 2 – a table which lists important attributes of the serial data stream. The table can inform the oscilloscope user of important characteristics of the whole signal without him needing to zoom in and look at each piece of the signal in detail. By examining the table the user can find the pieces of the signal that are of the most interest, click on the entry in the table and the scope will automatically zoom to that portion of the signal.

Figure 2: The capture of an ARINC 429 signal on the upper trace, a zoomed portion on the same signal on the lower trace and a table showing key signal characteristics.

Identifying and Trouble Shooting Problems

At the R&D stage every project suffers from some sorts of problems. In an avionics system it is particularly important to identify any potential pitfalls either in the data/command transmission system or in the devices which communicate via that system. The ARINC 429 option from LeCroy allows an oscilloscope user to search a captured signal record using a choice of 14 selectable criteria. These include the time of occurrence of a portion of the captured signal, data value, parity, message, status and other signal attributes. The MIL-STD-1553 option goes one step further and allows the scope user to set up a trigger to capture and decode exactly the portion of the signal in which the user is interested. Figure 3 shows the trigger setup menu where the user can choose the type (transfer, word, error and timing), subtype (command, data, status, any), format (binary, hex) and command. The oscilloscope will then monitor the live signal coming into the specified channel of the scope and trigger on the desired type of signal. As examples, being able to trigger on a specific command or being able to monitor the signal and trigger on any error are very powerful ways of testing and debugging problems.

Figure 3: Setting up a trigger for MIL-STD-1553. The user can select the type, subtype, format and command.

Summary

Modern digital oscilloscopes can greatly speed product development time and minimize the possibility of glitches in aerospace systems. In addition to capturing and decoding avionics specific signals such as ARINC 429 and MIL-STD-1553 it is also possible to do the same sort signal acquisition, decode and trouble shooting on ubiquitous signals such as USB, RS232, UARTs, and a wide variety of other types of serial data.

For more information on Lecroy Oscillocopes – click here: Lecroy

Written by: Dr. Michael Lauterbach
January 11, 2012

In some ways, induction lamps are a subset of fluorescent lamps. The light emitted from the lamp comes by transferring the energy from ultraviolet waves (UV) to a fluorescent coating on the inside of the bulb. The fluorescent coating converts the UV into visible light and the glass wall of the bulb absorbs any remaining UV. So only the visible light is emitted. The coloration of the light depends on the types of fluorescent used to coat the inside of the bulb.

But the method of producing the UV in typical fluorescent lamps is much different than the process used by induction lamps. UV is produced by establishing an arc discharge. In the case of the conventional fluorescent lamps the arc termination is at tungsten filaments (electrodes) at each end of the tube. An electrical current sustains the arc. The electrons in the arc through the lamp stimulate mercury vapor in the lamp thereby producing the UV waves that in turn excite the phosphor. Once the lamp starts up, it becomes a device with negative resistance – the more current that flows in the lamp, the lower its resistance becomes. So a ballast is required to moderate the flow of energy.

By contrast, induction lamps do not have filaments. This is also a huge difference from conventional fluorescent bulbs where the arc goes from one electrode to the other. The induction lamp has one continuous arc, eliminating the need for the wear out electrodes. Induction lamps work on the same principle as transformers, commonly encountered by electronic design engineers in power supplies. An alternating current passing through a conductor (the “primary:) will generate a magnetic field whose strength varies with the amount of current. The time varying magnetic field will induce a current in a nearby conductor (the “secondary”).

In the case of induction lamps, the 50-60 cycle AC line current is stepped up to RF frequencies. The wire carrying the RF signal is wrapped around a ferrite core that is exterior to a bulb containing mercury gas. The wire wound core acts as the primary of a transformer and the gas is the secondary. The energy transferred by this process excites the gas and it starts to emit UV. An electronic ballast is used to control the start-up and steady state operation of the bulb. These types of lighting devices can be highly efficient and long lasting. Efficiency is rated in lumens of light output per watt of power consumed.

An Example of Testing an Induction Lamp

Both the efficiency and the longevity of an induction lamp depend crucially on the ballast used to control it. In many cases this is a microprocessor controlled circuit – and considerable design and test expertise is needed to create a reliable, low cost yet effective ballast. Typically, a lighting device needs to operate in AC circuits with voltages ranging from 108 to 270 volts and frequencies of 50-60Hz. Figure 1 shows an example of testing on an induction lamp. In this case, the lamp ignition is having a hard time starting. The input voltage is 277 volts. This should be stepped up to about 450 volts and 200 kHz to operate the lamp. The upper half of the oscilloscope screen shows the capture of four signals over the course of one second during start up. Note the time/div in the lower right corner is 100 ms/div and there are ten horizontal divisions on the screen. The lower portion of the screen shows a zoomed detail at 20 ms/div of the four upper traces – basically, the zoom shows the portion of the signal captured in the 2nd and 3rd horizontal divisions of the upper grid. In the upper grid you can see highlighting on the early portion of the signal which indicates which piece of the signal is being shown in the zoom.

Figure 1: Failed ignition of an induction lamp operating at 277 volts. The upper grid shows one second of capture time for four signals. The  highlighted portions of those signals are shown as zoom details in the lower grid. Channel 1 (orange) is the rail voltage, Channel 2 (red) is the boost diode current, channel 3 (blue) is the bias supply voltage and channel 4 (green) is the output voltage of the lamp.

Channel 1 (orange) is the rail voltage which should be boosted to 450 volts. Note in the lower left corner of the screen the sensitivity of channel 1 is 100 Volts/div. In the highlighted portion of the lamp start up channel 1 only reaches (just barely) the fourth division, 400 volts. If you examine the upper trace you can see it reaches 450 volts about half a division later. Channel 2 (red) is the boost diode current (5 amps/div). For proper operation of the lamp, it should be running at a frequency of 100 kHz. In the zoomed detail you can see channel 2 is starting to switch current, but at a much slower rate than 100 kHz. Channel 3 (blue) is showing the charging of the internal bias supply to run the electronics (5 volts/div). It needs to be above 10 volts and though it eventually does get there (as shown in the upper trace), during the start-up portion of the signal shown in the zoom it never reaches 10 volts. Consequently, channel 4 (green) of the oscilloscope (1 kV/div) which shows the output voltage of the lamp reveals the lamp tries to start up and then fails.

Perhaps the first lesson concerning testing of induction lamps is that you need several types of probes to acquire the signals. Channel 3 i “easy”, just 5 volts/division so the typical probe supplied with the scope can handle it. For channels 1 and 4 the signals have much higher voltages so specialized voltage probes may be required. Channel 2 is a current ignal, so you either need a hunt to convert the current signal to a voltage or you need to use a current probe capable of capturing AC currents at frequencies up to at least 200 kHz.

When you want to use an oscilloscope to examine multiple signals and multiple zooms or multiple math traces it is good practice to use multiple grids. The ADC (analog to digital converter) on the front end of a typical 8 bit oscilloscope has 1 part in 256 resolution to measure the amplitude of the signal. If a ope is set up to display many signals on a single grid the user “squashes” each signal to fit a small vertical portion of the grid. Since the ADC is spreading its dynamic range across the full vertical height of the grid, if a ope user place a signal to fit into one vertical division (in order to see 8 signal shapes on a single grid) the scope winds up using only one eighth of its codes, 32 counts, to digitize the signal. Essentially, the user has paid for eight bit ADCs but is only using hem as 5 bit ADCs. Note in the upper grid on Figure 1 that each of the four signals is occupying about half of the vertical range of that grid – which means the four signals are each being digitized using half of the vertical range of the ADC. In an optimal case, the user would want the signals to cover near the full range of the grid, but in actual engineering practice, some headroom often needs to be left in case the signal goes higher or lower than expected. Also, in this case, no precision measurement is needed. The scope is operating more as a simple viewing tool. The shapes of the signals are enough to confirm the lamp is not operating properly.

Second Example of Induction Lamp Testing

A second example of testing the same induction lamp is shown in Figure 2. This time the basic operating conditions are 208 volts and 60Hz. The ignition sequence is better than in Figure 1 but still not sufficient to get the lamp started during the one second of time captured by the oscilloscope. The four traces (and the four zooms) are all still the same signals as in Figure 1, the horizontal time base of the acquisition and the zoom are the same and the vertical sensitivities (volts/div and current/div) are also the same as in Figure 1. The highlighted
area of the upper traces is now the 4th and 5th horizontal divisions of the upper grid. You can see the orange trace on channel 1, the rail voltage, reaches 300 volts near the end of the first horizontal division on the upper grid and eventually gets to the targeted 450 volts near the end of the zoom portion. But during the crucial time where the
lamp is starting up (as shown in the green trace on channel 4) the rail voltage oscillates at around 300 volts. Channel 2, in red, shows the boost diode current attains a much higher frequency than in Figure 1. In the zoom you can see a comb shape of quickly changing diode current. Channel 3 (blue), attains the 10 volts desired for the bias supply charging voltage shortly after the third division on the upper grid. But as the light starts to turn on (channel 4, the green trace) the bias voltage is disrupted. You can see bursts of noise on channel 3 which line up with the bursts of current on channel 2. The lamp fails to stay on and all four signal collapse back to steady states.

Figure 2: The same test setup as Figure 1 but this time the input voltage is 208 volts rather than 277 volts.

In addition to the oscilloscope usage lessons discussed above in the first example there are a few new points that arise. In Figure 1 the activity of the boost diode current could be clearly seen as nine fairly slow peaks of roughly triangular shape. But in Figure 2 the same signal has much faster activity. This could be viewed more clearly if channel 2 was zoomed to a faster time base. Some oscilloscopes only allow one common timebase for all zoom traces, as is shown in both figures. But in many real world test situations there are both slow signals and faster ones. So it can be desirable to have multiple zoom timebases. Many LeCroy oscilloscopes have this capability. You can even have a zoom of a zoom – perhaps turning on a 3rd and 4th grid that showed just the green and red traces on faster timebases than the existing zoom. That is a useful tool for viewing details of multiple signals. And there is a useful technique for measurements in this situation. Is the boost diode current running at its desired 200 kHz ? You can’t tell from Figure 2. But if the scope was set up to show the boost diode current on a third grid, at a faster zoom display timebase you could visually ascertain the frequency , you could do an FFT of the faster zoom trace or apply a parameter measurement to that trace. Using a zoom to select of portion of a waveform for measurement is a good technique. If you want to ignore a portion of a signal and just do math or
parameter measurements on a piece of the signal, you can activate a zoom to select the interesting portion of the signal, then apply math or parameters to the zoom trace (only).

A similar sort of capability with respect to measuring parameter values on just a portion of the signal can be accomplished using a feature called a “measure gate.” Oscilloscopes with this feature (including many LeCroy oscilloscopes) allow the user to turn on two vertical cursors and use them to define the piece of the signal to use in making parameter measurements. The measure gate can be placed on the original acquisition channels or it can be placed on a zoom. In both Figure 1 and Figure 2 the user has placed a measure gate on the lower grid.

In Figure 1 the vertical dashed, black lines can be seen to line up with the start and end of the burst of activity on the green trace (the lamp output voltage). In Figure 2 the measure gate is noticeably inside the envelope of lamp activity. The oscilloscope user can even move the measure gate to see if parameter values are different on various portions of the signal. Is the diode switching frequency (red trace) the same in the first burst of activity as 2nd, 3rd, etc?

There is one final point. Suppose you have the lamp shown in Figures 1 and 2 – and when you flip a switch it turns on? Certainly the view shown of the signals during one second of acquisition time does not look good. But maybe after the circuit has a few aborted tries it starts to work and the ballast regulates the light. What you might need is an oscilloscope with a longer acquisition memory in order to record the complete action of the lamp. If you look at rectangle near the lower right corner of both Figure 1 and 2 you can see the oscilloscope is capturing “10.0 MS” which means ten million samples of data on each of the four input channels. You can also see the sampling rate is “10 MS/s” – 10 million samples per second. This sample rate is clearly a good one for capturing the sort of details in this application. Let’s suppose you could keep the sampling rate the same, but instead of capturing one second of data you would like to capture for three seconds. You would need 30 million sample points. There are a couple of ways to do this. Some oscilloscopes have very long memory and you can simply go into the horizontal setup menu and tell the oscilloscope to use more. In other cases, you can sacrifice the number of input channels acquiring data in order to have longer memory available for the channels that are in use. An example is the WaveSurfer MXs-B from LeCroy (though there are also many other types of scopes with this capability). If you use all four channels of this type of scope, there are 16 Mpts of memory per channel. But the scope can also be told to operate in 2 channel mode and apply 32 Mpts of memory to each channel. So you could capture 3.2 seconds of data on 2 channels at 10 MS/s sampling rate. In order to test the operation of your lamp, maybe you only really need to see channel one and channel two of the two previous examples. Or, if desired, you could capture two signals, save them to internal memory in the scope, then capture two more signals. So you could even have all four signals – but use two acquisitions to acquire them.

Summary

There are many different types of interesting and useful lighting devices. To obtain longer lasting and more efficient lighting, good R&D engineering and careful testing are needed. This necessitates a wide variety of probes and can be enhanced by a knowledge of how to use the measurement capabilities of oscilloscopes.

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Written by: Dr. Michael Lauterbach
January 18, 2012