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Know your power supply jargon: watts vs. volt-amperes

Written on December 5, 2016 at 10:56 am, by

To select the right power source for your applications, one of the first things that you must do is to figure out how much output power you need. For a DC supply, this is relatively straightforward. You first determine the highest output voltage you’ll need and then the highest output current that you’ll need. The output power (in watts) is equal to the output voltage times the output current:

P (W) = Vout X Iout

In some applications, of course, you may not need the maximum output current and the maximum output voltage or vice versa. To be on the safe side, however, if you choose a power source that can supply the highest voltage and the highest current that you’ll need, then you can be sure that the power source is not underpowered for your application.

DC power calculated with the formula above is sometimes called real power or true power. We call this real power because it is the amount of power that’s actually available to do some work. This could include running DC motors or powering an electronic unit under test.

Apparently, not quite so real

For an AC power source, this calculation isn’t quite so simple. The reason for this is that for some, if not most, AC loads, the voltage and current are out of phase with one another. If the load is capacitive, the current will lead the voltage. If the load is inductive, the voltage will lead the current.

Reactive loads make a power source work harder because they require a power source to supply power during a portion of an AC cycle, only to return a portion of that power later. The net effect is that a power source has to be able to supply more current than that calculated by the equation for calculating DC power.

Because this power doesn’t do any real work, it is called apparent power or virtual power. To differentiate apparent power from real power, we use the unit volt-ampere, or var, instead of watts. The abbreviation for volt-ampere is VA. The equation used to calculate the apparent power is

P (VA) = Vrms x Irms

where Vrms is the root mean square value of the AC voltage and Irms is root mean square of the AC current.

The ratio of the real power to the apparent power is called the power factor (PF):

PF = real power (W) / apparent power (VA)

If you know the phase shift between the voltage and current, you can calculate the power factor using the equation:

PF = cos ø

where ø is the phase angle between the voltage and the current.

The power factor will always be between 0 and 1, and the greater the phase angle, the smaller the power factor. The smaller the power factor, the greater the apparent power, meaning that you’ll need a supply with more output power to power a highly reactive load than you will need to power a load with only a very low reactance.

For more information on this topic and AMETEK Programmable Power’s AC, DC, and AC/.DC power sources, contact AMETEK Programmable Power. You can send e-mail to or phone 800-733-5427.

Choose the right features for your next adjustable DC power supply

Written on November 30, 2016 at 6:00 am, by

The Sorensen XEL benchtop DC power supplies are user-friendly, supply up to 180W, and have advanced digital features.

The Sorensen XEL benchtop DC power supplies are user-friendly, supply up to 180W, and have advanced digital features.

Although oscilloscopes and spectrum analyzers have flashy features, and get most of the attention, there is no instrument more useful to an electronics engineer than the lab DC power supply. It’s used for nearly every design, prototype, and test activity, and a supply that doesn’t have the right features, can not only hinder your productivity, but compromise your designs as well. That being the case, it might be a good idea to take a look at the lab supply that you’re currently using and think about upgrading.

Here is what you should consider when choosing adjustable DC power supply features:

Linear output regulation

Watt for watt, switching supplies are smaller than linear supplies and offer more control features, but linear supplies are often a better choice for benchtop work. On the bench, power density is usually not an issue, and linear supplies have lower output noise specifications than switching supplies. (For more information on this topic, see “Are linear supplies or switching supplies the best choice for your test system?”)

Multiple outputs

For many applications, you’ll need more than one output, and while you can connect multiple supplies to a system or circuit under test, that can be kludgey. When buying a supply with multiple outputs, look for one that has isolated outputs, so that they can be operated separately or in parallel. Another useful feature for a multiple-output supply is a tracking mode that lets you control both outputs with a single control.

Control flexibility

The easier it is to set up a power supply, the more productive you will be. Separate controls for voltage and current is a must on a lab DC power supply, and the voltage control should either be a multi-turn control or there should be a separate fine tune control. These controls should allow you to quickly set the output voltage to exactly the value required.

Another useful feature is the ability to lock the voltage and current settings at specific values. This prevents you or a technician from accidentally bumping the controls and changing the settings while you’re debugging or running a test.

Another safety feature is the ability to set the span of the voltage output control. Setting the min and max values of this control gives you more precise control of the output voltage and protects your system or circuit by preventing you from setting an output voltage that’s too high.

Output enable/disable

With this feature, you can switch the output on or off without turning the supply off completely. With this feature, you can set up the supply without worrying how your adjustments will affect the load.

PC control functions.

For many benchtop applications, PC control is not really necessary, but if your lab DC power supply does have remote control capability, you will be able to automate many of the repetitive tests you run in your lab. In many applications, doing this will improve your productivity.

The Sorensen XEL Series offers all of these features and more. For more information on the XEL Series and AMETEK Programmable Power’s other benchtop supplies, you can send e-mail to or phone 800-733-5427.

Know Your Electronic Load Modes

Written on November 11, 2016 at 7:29 am, by

Electronic loads, such as the Sorensen SL Series of DC Electronic Loads, are instruments that you would use to provide a programmable load when testing voltage and current sources, including power supplies and batteries. Modern electronic loads are actually sophisticated electronic test instruments that can offer a number of different modes, including Constant Current (CC) mode, Constant Resistance (CR) mode, Constant Voltage (CV) mode, and Constant Power (CP) mode.

CC Mode

In Constant Current (CC) mode, the load will sink a current equal to the programmed current setting regardless of the input voltage, up to the maximum current rating of the load. You might use the constant current mode to ensure that your power supply can output the maximum specified current under all conditions.constant-current-mode

CR Mode

In Constant Resistance (CR) mode, the electronic load will act like a fixed resistor. It senses the voltage at its input and sinks a current linearly proportional to the input voltage. You might use the constant resistance mode to test the capacity of batteries. Constant resistance mode is also most often used to measure the start-up conditions of electronic devices.


CV Mode

In Constant Voltage mode, the load will attempt to sink enough current to maintain the programmed voltage setting at its input terminals. Of course, if there are some limitations on how much current that the load is able to sink.


CP Mode

In Constant Power (CP) mode, the load will attempt to sink whatever load power is programmed. It senses the voltage at the input, calculates the appropriate current, and then attempts to sink that amount of current. You might use this feature to ensure that your power source is able to supply the specified output power over the entire output voltage range of the source.


A very similar curve is the power contour of the electronic load. In practice, the power contour curve of an electronic load shows how much current that a load can sink at various voltages when programmed to their maximum power level. The figure below shows the power contour for a Sorensen SLM 60-60-300 Electronic Load. It has a maximum input voltage of 60 VDC, a maximum input current of 60 A, and a maximum power capability of 300 W.


For more information on electronic loads, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

The 3 BIG questions that you have to ask when buying a power supply

Written on November 7, 2016 at 5:41 am, by

It wouldn’t be bragging to say that we have a lot of experience with power supplies here at AMETEK Programmable Power. Many of our design and sales engineers have been with us for a long time, and we feel that really gives us an edge when it comes to helping you get the best product for your needs. Their extensive knowledge of our products and applications enable them to recommend just the right products, and you can feel confident in their recommendations.


You can control the new Asterion Series AC/DC power source via the intutitive front panel user interface.

When it comes to specifying a power source, one of AMETEK Programmable Power’s sales engineers is famous for getting right to the crux of the matter. He says that there are three questions that every customer must ask himself or herself before buying a power supply. They are:

  • What do you want out of it?
  • What are you going to feed it?
  • How are you going to control it?

What do you want out of it?

Specifying the outputs of a power supply is the first task. The primary considerations are:

  • Type of output: AC, DC, or both AC and DC
  • Power output
  • Voltage range
  • Current capability

While those may be the three most important parameters, they are not the only output specifications that you need to take into account. Another important parameter is the slew rate. The slew rate of a DC power supply is the rate at which the output voltage and output current changes. This characteristic is important in many applications, especially automatic test applications, as the faster a supply reaches a programmed voltage or current, the faster a test will run.

In other applications, ripple and noise, line regulation, load regulation, or similar specifications might also be important. Based on their experience, our sales engineers will ask you a number of questions about your application, to ensure that you get the right power source.

What are you going to feed it?

Once you’ve determined what you want out of a power supply, the next question to ask is how are you going to feed it. By that we mean how are you going to supply the input power.

For most power supplies over 1,500 W or 1,500 VA, you can’t simply plug the supply into a 120 VAC wall socket. At the very least, you’ll have to supply 220 VAC single-phase power, and if you have very high power requirements, then you’ll have to supply some form of three-phase power.

Before you purchase a supply, consult with your facilities management people to see what’s available in your lab or on the manufacturing floor. That way, you’ll be sure to purchase a power supply with the right input power configuration.

How are you going to control it?

There are many different way to control a power supply. Many are just controlled manually. If you plan to control yours this way, ensure that the front panel interface is intuitive and easy to use. A good example of an intuitive front-panel user interface is found on AMETEK’s Asterion line of power sources.

For computer control, you can choose between Ethernet LXI, USB and RS232 interfaces. The interface you choose will depend on many different factors including the interfaces that you already use in your company, the data transfer rate required, and other factors. For more information on the right interface for your application, or how to select a power supply in general, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

Analog control for a power supply still a good choice for many applications

Written on November 2, 2016 at 6:33 am, by

While these days, computer control is usually the preferred method of controlling a power supply, many AMETEK Programmable Power products, such as the Sorensen SGA Series still offer analog control. Analog control is still used in many industrial applications, and it’s also a good choice if you have fairly simple control needs.

The SGA Series allows you to control the output with an analog signal in eight different ways:

  • Turn the power supply on and off with an analog signal, switch closure, or TTL/CMOS signal.

  • Set the output voltage with a 0 – 5 VDC signal.

  • Set the output voltage with a 0 – 10 VDC signal.

  • Set the output voltage by resistance (0 – 5 kΩ).

  • Set the output current with a 0 – 5 VDC signal.

  • Set the output current with a 0 – 10 VDC signal.

  • Set the output current by resistance (0 – 5 kΩ).

  • Set the over-voltage protection (OVP) trip level with a 0.25 – 5.5 VDC signal.

You connect the control signals to an SG Series power supply via J1. It is labelled “ANALOG CONTROL.”

Setting the output voltage with a 0 – 5 V signal

As an example, let’s look at how to use a 0 – 5 VDC signal to control the output voltage. As shown in Figure 1 below, you connect the DC voltage source between J1, pin 9 (VP 5 V) and J1, pin 20 (VP RTN). Note that VP RTN must be within ±3 V, of the circuit common (J1, pin 6, COM). In this example, we connect pin 20 directly to pin 6 (COM), so it’s at the same potential. J1, pin 5 is the ON/OFF input and must be connected to COM to enable the power supply output.


When connected this way, the output voltage, Vout = (Vdc/ 5 VDC) * 100% rated output voltage, with Vdc in volts.

Details on how to connect and use the other analog control signals can be found in the Sorensen SGA Series DC Power Supply Operation Manual.

Isolating control signals

In some applications, you may need to isolate these control signals from the power supply. To do this, you need the Remote Isolated Analog Interface Control Option.

This option uses the same Analog Control connector (J1) as the standard interface, but fully isolates the remote control signals and allows control of units not connected to a common ground. Control signal returns are isolated from output power negative terminal. Isolating these signals protects the power supply from potential damage from systems with high energy electrical potentials or large ground loop currents.

For more information on how to use remote analog programming, or isolating control signals, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

Five mistakes engineers make when choosing power supplies

Written on October 27, 2016 at 6:38 am, by

The power supply may be one of the least-considered components of an electronic system. After all, how hard can it be to find the right power source for your system? You figure out how much current you need at the voltage your system will operate at, find a model that can supply that voltage and current in a catalog or on a website, then make the purchase.


Asterion’s ix2 current doubling technology allows Asterion power sources to linearly increase the output current and maintain maximum power output over a wider output voltage range. See #2.

Actually, it’s not that simple. There are many other things that you need to think about choosing and using a power supply. Here are five common mistakes that engineers make when choosing and using a power source for their projects:

  1. Not buying a supply with enough output power. While you certainly don’t want to buy a supply with too much excess power output, trying to save money by buying a supply with just enough power output isn’t a good idea, either. Buying an undersized power supply won’t save you money if you have to replace it with high power supply at some later date. To avoid this, consider future as well as current needs and buy a supply with at least 25% capacity above current needs.

  2. Not buying a supply with enough output current. Even though a power source might be able to supply a certain amount of power, it’s not a given that it can supply every voltage/current combination. For example, a 1,500 W DC power supply with a 400 VDC range may only be able to supply 3.75 A maximum across the entire range.

    AMETEK’s Asterion power sources overcome this limitation by using iX2 current-doubling technology. iX2 current-doubling technology allows Asterion power sources to linearly increase the output current and maintain maximum power output as the output voltage drops from the maximum output voltage to half that value. No other power source can deliver full output power over such a wide voltage range. iX2 current-doubling technology eliminates the need to buy multiple sources or overpowered sources to run tests at low line voltages.

  3. Not considering startup conditions. Many AC-powered products, such as switching power supplies and electronic lighting ballasts, draw high start-up currents to charge capacitive circuitry. Excessive inrush currents not only cause lights to flicker, but can also damage the power supply. Depending on what you’re powering, the power source may have to be able to supply this amount of inrush current.

  4. Not paying enough attention to wiring. Once you’ve selected the appropriate power supply for a system, you need to connect it to the system. If you’re supplying high currents, make sure that you select power cable large enough to handle that current. Refer to the National Electrical Code for these values.

    One rule of thumb is to keep the leads as short as possible. This will minimize the voltage drop in the power cables. When tolerances are tight, consider using a feature called remote sensing. AMETEK power sources with this feature allow you to sense the voltage with a second set of wires at the power input to a system and regulate the output voltage based on this value.

  5. Poorly designed rack mounting. Because many of AMETEK Programmable Power’s power sources are designed to supply relatively high power, they are often mounted in a 19-in. rack. One is a lack of cooling. Always ensure that the equipment in a 19-in. rack is properly ventilated to keep operating temperatures within specification.

For more information on choosing and using AC and DC power sources, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

Power Source Multi-Box Configurations Meet a Variety of Needs

Written on October 25, 2016 at 11:17 am, by

Many of AMETEK Programmable Power’s AC power sources are designed to work as both standalone units and in multi-box configurations. The California Instruments iX Series AC/DC power sources, for example, includes independent 5 kVA power modules that can be combined into a number of configurations. You might use a single unit as a high-power, single-phase system or configure three units to form a medium-power, three-phase system. This modularity allows you to build a power system that meets your specific needs.

To do this with the ix Series, you need to purchase the Multi-Box option (-MB). This option includes the additional test and calibration required for a multi-box system, as well as the additional cabling needed to configure a multi-box system.

Standard three phase iX configuration

The standard, three-phase iX series configuration uses a single master unit with a three phase controller to drive two additional slave units. Figure 1 shows a standard 15003iX configuration, which provides a total power of 15 kVA and can be used in either single-phase or three-phase mode. Also available is the 30003iX configuration. This configuration can supply up to 30 kVA, but operates in three-phase mode only.


As shown in Figure 1, the master provides phase A output, while the slaves are used to provide output for phase B and C. Neither slave unit has a controller since the master unit controls all three via the system interface. This connection consists of a ribbon cable that connects all three units together.

More controllers means more flexibility

In addition to the 15003iX or 30003iX configurations, you can specify a system to have three single-phase, 5 kVA units with controllers in the slave units. In this configuration, the controller in the master unit still drives the two slave units through a system interface connection, and users can control all three phases from a single front panel and operate in a phase locked mode.

When operating in phase-locked mode, the slave unit controllers must disabled, but the additional cost for the controllers units is offset by enhanced flexibility. For example, a 15003iX-MB system in which each unit has a controller allows you to configure the system in the following ways:

  • 15 kVA 3 ø system
  • 15 kVA 1 ø system
  • 10 kVA 1 ø system and (1) 5 kVA, 1 ø system
  • 5 kVA, 1 ø systems

Three-phase systems may be broken up into individual single-phase AC/DC sources to be used in different test stands. It is even possible to combine several single phase units into a higher power single-phase system by paralleling the output of two or three 5 kVA units to create a 10 kVA or 15 kVA single-phase system.

Single phase systems only require a single controller. If multiple units are used in parallel, the master unit’s controller is used while slave controllers are disabled, and you control the system with a single front panel. The following configurations are possible with the 15001iX-MB:

  • 15 kVA 1 ø system
  • 10 kVA 1 ø system and (1) 5 kVA, 1 ø system
  • 5 kVA, 1 ø systems

When used in a multi-box configuration, the California Instruments iX series allows you to configure an AC/DC power system that meets the needs of a wide array of applications and eliminates the need to purchase many different AC or DC power sources. For more information on configuration options, download Application Note 118, “Multi-Box iX Series Configurations.” To discuss your application needs, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

Maximizing UPS Battery Life

Written on August 8, 2016 at 12:26 pm, by

GUPS_Main_ImageThe Elgar GUPS Series of uninterruptible power supplies are ruggedized on-line UPSs that accept a broad range of worldwide utility and military AC input power. Without operator intervention, they automatically select the appropriate input power ranges to accommodate global operation. The batteries used in the GUPS Series units are a spiral wound, valve-regulated, lead-acid batteries. While the unit itself maximizes battery life with automatic, microprocessor-controlled equalization and temperature compensation during charging, there are steps that users can take to extend UPS battery life even more.

What shortens UPS battery life?

Sulfation, a natural electrochemical reaction in lead acid batteries, is the primary culprit, but other phenomena also shorten UPS battery life. These include:

  • nonoperational discharge,

  • cell impedance,

  • operating and storage temperature,

  • the number and depth of discharges and charger characteristics.

Sulfation. In normal operation, a chemical reaction between the sulfuric acid electrolyte and the lead plates in a battery forms lead sulfate crystals. These crystals behave like insulation, hindering the battery’s ability to accept a charge. Sulfation also causes an increase in cell impedance. The rate of sulfation increases when the battery is exposed to higher temperatures, when the battery is stored for a long time without a recharge, and when the battery is stored in a discharged state.

Non-operational discharge. Even when powered down, the GUPS Series units draw a small current (300-500 µA). Users can remove the battery drawer from the GUPS chassis, but the batteries will continue to self-discharge when not in use. If the GUPS is stored without being recharged after the battery is used, the additional self-discharge will damage the battery

Cell impedance. Sulfation causes an increase in cell impedance, and eventually this increase in impedance will reduce the battery’s output voltage full charge. Sooner or later, the batteries will be unable to power the GUPS.

Operating and storage temperatures. Higher operating and storage temperatures reduce battery life by increasing sulfation rates.

Number and depth of discharges and charger characteristics. When operating a GUPS at higher temperatures, the charge voltage must be temperature-compensated by reducing the voltage to avoid an over voltage. At lower temperatures the charge voltage must be temperature-compensated by increasing the charge voltage to prevent undercharging. Although these charger related parameters are outside an end user’s control, they are taken into account in the GUPS system design.

How to make batteries last longer

While it is impossible to eliminate sulfation or self-discharge, there are some things that users can do to improve battery life, including:

  • recharge a discharged battery before storing it,

  • store the battery at a cool temperature, and

  • charge a battery for 72 hours prior to using it after it has been in long-term and/or high-temperature storage.

Another thing that users can do is to control operating temperatures, When and where possible, reduce the operating temperature will reduce sulfation, thereby extending battery life.


  • Keep the battery charged and cool.

  • Remove the battery drawer from the GUPS chassis if you need to store the batteries for more than 30 days.

  • Do not store the battery drawer in a discharged state.

  • Recharge the battery after use and before storing.

  • Store at lower temperatures. A fully charged battery drawer can be stored for 10 months at 10º C, but at 40º C this is reduced to 1.5 months.

  • Before use after long-term storage, charge the batteries in the chassis for 72 hours.

Finally, consider placing the GUPS batteries on a cyclic life-extension maintenance schedule where the chassis-in-use is swapped out with a stored battery drawer, at intervals frequent enough to minimize the effects of long-term storage, storage at high temperatures, and self-discharge.

For more information on the GUPS Series of uninterruptible power supplies, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.

Introduction to IEC 61000-4-11, Part II – AC source requirements

Written on August 2, 2016 at 7:04 am, by

In Part I, we introduced you to the concept of testing equipment for immunity to voltage dips and short power interruptions in accordance with IEC 61000-4-111. In addition to specifying the test waveforms, the standard also specifies AC source requirements for full compliance testing.

Most of these requirements are easily met by the California Instruments iX Series AC/DC power sources. Some, however, are not trivial and warrant more attention:

  • 500 A EUT inrush current capability

  • 1 to 5 msec rise and fall time at source output

  • Current capability at reduced voltage levels

The inrush current requirement of 500 Amps however is not practical, as it would raise the price of the AC source considerably. Since most EUTs don’t draw this kind of inrush current, sizing an AC source for this current level is impractical. Instead, the standard allows the source to measure the peak inrush current to the EUT and verify that it does not exceed the capabilities of the AC source. Our instrument control software provides a “peak inrush current pre-test” option in the IEC 61000-4-11 test window for this purpose. If the peak inrush current of the EUT, as defined in the IEC standard, exceeds the AC source capability, a warning is issued to the operator.

To fully meet the AC source qualification for IEC 61000- 4-11 testing, option -EOS can be added to the iX Series AC/DC power source to ensure output rise and fall times between 1 and 5 micro seconds. This option also ensures the source’s ability to deliver higher rms currents at reduced voltage levels for constant power products. Specifically, 5001iX with -EOS option meets the 23 A at 70% and 40 A at 40 % of Unom requirement called out in the IEC 61000-4-11 standard.

Pass/fail criteria

The pass/fail criteria in IEC 6100-4-11 is rather vague. It says,

“The test results shall be classified on the basis of the operating conditions and functional specifications of the equipment under test, as in the following, unless different specifications are given by product committees or product specifications.

a) Normal performance within the specification limits.

b) Temporary degradation or loss of function or performance which is self-recoverable.

c) Temporary degradation or loss of function or performance which requires operator intervention or system reset.

d) Degradation or loss of function which is not recoverable due to damage of equipment (components) or software, or loss of data.

As a general rule, the test result is positive if the equipment shows its immunity, for the duration of the application of the test, and at the end of the test the EUT fulfills the functional requirements established in the technical specification.”

When using the iX Series to perform these tests, you can use the source to measurement measure the load current of the device under test to determine if it is still operating after applying the voltage dips and interruptions. Note, however that this measurement doesn’t really determine if the unit is really functioning, only drawing power. For example, if you’re testing a microprocessor-controlled device, the processor may have locked up or rebooted during the test. In this case, you may want to run some kind of functional test to determine if the device has passed or failed the test.

For more information on IEC 61000-4-11 testing, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.


  1. IEC 61000-4-11:2004, Electromagnetic Compatibility (EMC) – Part 4-11: Testing and Measurement Techniques – Voltage Dips, Short Interruptions, and Voltage Variations Immunity Tests. International Electrotechnical Commission.

Introduction to IEC-61000-4, Part I

Written on July 25, 2016 at 1:14 pm, by

Mains voltage dips and short interruptions can be caused by a wide variety of phenomena and can cause equipment to operate unreliability, and in some cases, can damage the equipment. Faulty loads on an adjacent branch circuit, for example, can cause a circuit breaker to trip, and high-power loads such as welders, motors and electric heaters can cause voltage variations. Natural events, such as power lines downed by storms or lightning strikes, may also disrupt mains power.

If the fault is in the power distribution grid, an automatic recovery circuit may cycle open and closed several times within a short period attempting to clear the fault. This will likely result in a sequence of short voltage interruptions as seen by downstream loads.

Voltage variations are typically caused by high power loads that have continuously varying power requirements. These voltage changes can affect the operation of nearby electrical and electronic equipment and sometimes even damage it.

To ensure that products can withstand these interruptions and voltage variations and operate safely and reliably, you must test them under a variety of conditions. IEC 61000-4-11, Electromagnetic Compatibility (EMC) – Part 4-11: Testing and Measurement Techniques – Voltage Dips, Short Interruptions, and Voltage Variations Immunity Tests, aims to standardize the way companies test how their products react to power line variations. Although it is a European standard, manufacturers use it worldwide for design verification testing.

IEC 61000-4-11 was first published in 1994 (Edition 1.0) and amended in 2000. Its scope includes electrical and electronic equipment with an input current rating not greater than 16A per phase. It is one of the required tests in the Generic Residential, Commercial and Light Industrial immunity standard EN50082- 1: 1997 and is also under consideration to be included in the Generic Industrial immunity standard EN50082- 2. It is also included in several product-specific standards such as the EN 61326-1 which went into effect in mid 1999 and covers testing instruments, data acquisition and control systems.

IEC 61000-4-11, edition 2.0, was released in March 2004. Edition 2.0 references IEC 61000-2-8, Environment – Voltage dips and short interruptions on public electric power supply systems with statistical measurement results. It differs from the first edition in the following ways:

  • Preferred test values and durations have been added for the different EMC environment classes 1, 2, 3 and user class X.

  • The recommended voltage dip and interruption durations are shorter.

  • A new test level of 80% of Unom was added for voltage dips test. The 70% test level remains as well, however, and is still used in all product standards.

  • Voltage variations are now done using an abrupt voltage change from Unom instead of a voltage sweep. The change from the reduced level back to Unom is still a sweep however.

  • All durations for voltage variations are now expressed in no. of cycles of the fundamental AC frequency instead of seconds. The number of cycles for 50 Hz and 60 Hz is chosen so that the time intervals are the same.

  • Tests for three phase systems have been specified.

Figures 1 through 3 show timing diagrams for various power disturbances specified by IEC 61000-4-11. Figure 1 shows a 40 % voltage dip. Figure 2 shows a voltage interruption. The duration of either is defined in number of cycles of the fundamental frequency. The actual change in voltage may occur at a set phase angle, e.g. 0° or 90°.


Figure 1. 40% voltage dip waveform specified by IEC-61000-4-11.


Figure 2. Voltage interruption waveform specified by IEC-61000-4-11.

Figure 3 shows the timing for a voltage variation. This waveform is different from the voltage variation waveform in edition 1 and better simulates the effects of motor loads starting up on the mains voltage.


Figure 3. Voltage variation waveform specified by IEC-61000-4-11.

In Part II, we will discuss test levels, the pass/fail criteria for IEC 61000-4-11 testing, and test generator requirements. For more information on IEC 61000-4-11 testing, contact AMETEK Programmable Power by sending an e-mail to or phoning 800-733-5427.