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Know Your Power Supply Jargon: Isolation

Written on May 24, 2017 at 7:51 am, by

The Sorensen XBT Series is one of AMETEK Programmable Power’s lines that offer isolated outputs.

Many AMETEK Programmable Power products offer isolated outputs. In this blog post, we’re going to discuss what power supply isolation means and why this characteristic is desirable.

An isolated power supply has a power output that is electrically independent of its power input. That is to say that there is no connection between the power input and the power output. When a power supply has multiple isolated power outputs, it means that the output voltages are independent of one another and there is no connection between the outputs.

There are several reasons why you might want to select a power supply with isolated outputs:

  1. Safety. Safety is perhaps the most important reason for a power supply’s outputs to be isolated from the AC supply voltage. Isolation prevents AC mains voltage from being present on the output. This is the reason that isolation is of extreme importance for power supplies used in medical equipment. IEC 60601-1: Medical electrical equipment – Part 1: General requirements for basic safety and essential performance is the standard that spells out requirements for power supplies used in medical applications.

  2. Flexibility. Benchtop power supplies with multiple, isolated outputs, such as the Sorensen XBT Series, offer users the most flexibility. The XBT’s isolated supplies can easily be connected in series to obtain higher output voltages or in parallel to obtain higher output currents.

  3. Ground loop prevention. Another reason to use an isolated power supply is to prevent ground loops. Ground loops occur when two or more circuits share a common return path. When your system has a ground loop, current flowing in the loop can cause one or more of the circuits to malfunction. Using an isolated power supply breaks the ground loop and prevents this interaction from happening.

Isolation between power input and power output or between two power outputs is never 100%. Insulators, for example, are not perfect and are conductive to some degree. This conductivity results in a leakage current. Insulators also have a finite breakdown voltage.

Other characteristics that reduce the level of isolation between two circuits are stray capacitance and mutual inductance. There is, for example, stray capacitance between the primary and secondary windings of a transformer, and this capacitance reduces the level of isolation between the power input and power output. Mutual inductance can also reduce the level of isolation between two circuits. If this is a problem for you, the solution is to increase the distance between the two circuits.

There are two ways to measure isolation between two circuits. One way is to measure the resistance. Because the resistances are so high—20 Mohms or more—you may need more than just a typical multimeter to make this measurement. Another way to measure isolation is to perform a “Hi-Pot” test. To run this test, you apply a high DC or an AC voltage across the two circuits and measure the leakage current. There are testers specifically designed to run this test.

In addition to isolated outputs, you might also want to consider whether or not a supply’s control inputs—both analog and digital—are isolated. Isolated inputs will help ensure that control circuits don’t affect the power supply output and vice versa. For more information on power supply isolation, contact AMETEK Programmable Power. You can send an e-mail to sales.ppd@ametek.com or phone 800-733-5427.

New AC/DC Power Source Makes Three-Phase Power More Affordable

Written on May 15, 2017 at 9:56 am, by

SAN DIEGO, April 4, 2017AMETEK Programmable Power has added a 22.5 kVA unit to its popular California Instruments MX Series II AC/DC Power Sources. The MX22.5 delivers up to 22.5 kVA and can be configured to have single-phase or three-phase outputs in AC, DC or AC+DC mode. The MX22.5 is more economical than the California Instruments MX30, while at the same time offers more features and higher output power than the product family’s MX15 model.

The California Instruments MX Series II provides controlled AC and DC output for a wide variety of automated test equipment and product test applications at an affordable cost. Using state-of-the-art PWM switching techniques, the MX series combines robustness and functionality in a compact floor-standing chassis, no larger than a typical office copying machine. And, this higher power density does not need elaborate cooling schemes or additional installation wiring. Simply place the unit in its designated location (using included casters), plug it in, and the MX Series is ready to operate.

The MX22.5’s innovative features include:

  • Simple operation.  The MX Series can be operated completely from its menu-driven, front-panel controller. A backlit LCD display shows menus, setup data, and read-back measurements.
  • Expandable power levels. Users can combine units to configure systems up to 135 kVA or more.
  • Switching between single-phase and three-phase outputs. Phase mode programming on MX22.5-3Pi allows users to easily switch between single-phase and three-phase output modes.
  • Arbitrary and harmonic waveform generation. Using the latest DSP technology, the MX Series programmable controller is capable of generating harmonic waveforms and arbitrary waveforms to test for susceptibility to harmonics and other power anomalies.
  • Regenerative, bidirectional “green” power. Automatic crossover between source and sink power modes offers regenerative capabilities in AC or DC mode. The power sources can regenerate up to 85% of the rated output power back to the utility grid during sink mode operation when equipped with the -SNK or -SNK-DC option.
  • Power measurements. The MX Series can make a wide variety of measurements in addition to supplying power, including frequency, Vrms, Irms, Ipk, crest factor, real power (watts), apparent power (VA), and power factor. These measurements  are accessible from either the front panel or the remote control interface.
  • Remote control. The MX Series can be equipped with RS-232C, USB, IEEE-488, and LAN Interfaces for remote operation and automated test applications.

For More Information
To learn more about AMETEK‘s programmable power supplies and programmable electronic loads, contact AMETEK Programmable Power Sales toll free at 800-733-5427, or 858-458-0223, or by email at sales.ppd@ametek.com.  Information also is available from an authorized AMETEK Programmable Power sales representative, who can be located by visiting http://www.programmablepower.com/contact.

About AMETEK Programmable Power
AMETEK Programmable Power designs, manufactures and markets precision, AC and DC programmable power supplies, electronic loads, application specific power subsystems, and compliance test solutions for customers requiring and valuing differentiated power products and services. It offers one of the industry’s broadest portfolios of programmable power products under the California Instruments, Sorensen, and Elgar brands.

AMETEK Programmable Power is a business unit of the AMETEK Electronic Instruments Group, a leader in advanced instruments for the process, aerospace, power, and industrial markets and a division of AMETEK, Inc., a leading global manufacturer of electronic instruments and electromechanical devices with 2016 annual sales of approximately $4.0 billion.

For further information contact:
Craig Frahm
Tel: (858) 678-4459
E-mail: craig.frahm@ametek.com
Website: www.programmablepower.com

Using an Adjustable Power Supply with Tracking Outputs

Written on May 15, 2017 at 9:50 am, by

Many op-amp circuits used in analog applications, such as signal conditioning for high bit count analog-to-digital converters require the use of both positive and negative power supply voltages, as shown in Figure 1. Supplying both positive and negative voltages allows input signals and output signals to swing both positive and negative. You could power these circuits with an adjustable power supply with two outputs and adjust them separately—one to the positive rail voltage, say +12 VDC or +15 VDC and the other to a similar negative voltage.

Many op-amp circuits require the use of both positive and negative supply voltages.

The problem with this approach is that it is cumbersome to adjust both supplies simultaneously and to get the two output voltages to be equal to one another. Another problem that can occur is that the op amp may “latch up” if the power-up sequence is not coordinated properly. This can damage the op amp or prevent it from operating correctly.

A better approach is to use an adjustable power supply with tracking outputs, such as the Sorensen XBT Series. The XBT Series provides three output channels, and channels 1 and 2 can be configured for parallel, series, or tracking operation. In tracking mode, channels 1 and 2 provide the same (but opposite polarity) outputs. In addition, the outputs can be isolated from one another, if desired. These two channels can supply 0 – 32 VDC with a maximum current of 3 A. Tracking accuracy is ± 0.02% + 10 mV.

It’s very easy to set up output tracking. From the front panel, simply press the CONFIG key, select TRACKing with the rotary control, then press the rotary control to turn tracking on or off. To turn tracking on or off via computer control, simply issue the SCPI command OUT:TRACK. Once tracking is turned on, Channel 2 will have the same voltage and current settings as Channel 1.

One of the ways that you might use this feature is to test the sensitivity of your circuit to power supply voltage. Programatically, you could ramp the power supply voltage up and down from say 9 VDC to 15 VDC in steps, performing a functional test at each step.

Keep in mind that the Sorensen XBT is a precision power supply. When powering your circuit from the power supply in your product, the performance of the circuit may vary from the performance you observe with the benchtop power supply. That being the case, it’s also necessary to thoroughly test your circuit with the production power supply.

For more information on adjustable power supplies and how to use tracking outputs, contact AMETEK Programmable Power. You can send an e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Electronic Load Selection: Volts, Amps, and Model Numbers

Written on May 15, 2017 at 9:43 am, by

Often the selection of programmable power supplies is based upon how high a voltage it can produce or how much current it can source. When selecting an electronic load, however, you need to consider not only volts and amps, but power as well. For example, the SLH-500-6-1800 has a maximum input voltage of 500 VDC and a maximum input current of 6 Arms, but that doesn’t mean that it can accommodate these voltages and currents under all conditions.

When specifying an electronic load for a particular application, you also have to look at the maximum power rating. In the case of the SLH-500-6-1800, that specification is 1,800 VA. From a practical point of view, what this means is that at 500 VDC, the maximum current that the SLH-500-6-1800 can sink is 3.6 A.

The power limit of any particular electronic load is given by its constant power curve. The power curve of the SLH-500-6-1800 is shown below.

A load must be selected so that the operating points are within the curve. For many applications in which different power sources are tested, there may be high voltage, low current requirements as well as low voltage, high current requirements. A single load may be able to handle both with good programming resolution. In cases where a single load may not work, the broad range of current, power and voltage available in the Programmable Power SL series allows optimum selection depending upon the voltage, current, and power required.

This brings us to the matter of model numbers. All of the models in Programmable Power’s SL Series of electronic loads have model numbers that tell you the maximum voltage, maximum current, and maximum power dissipation of the unit. The first number gives the maximum voltage, the second number the maximum current and the third number the maximum power dissipation. In the case of the SLH-500-6-1800, that’s 500 VDC, 6 A, and 1,800 VA.

Finally, a word about low-voltage operation. All SL series loads operate well below 1 V, but in many applications, such as fuel cell research and microprocessor voltage regulator modules (VRMs), the voltage at the load inputs can be 0.1 to 0.2V. This low voltage does not allow the load transistors to fully turn-on (bottom right corner of the power contour). To utilize the full rated current of an electronic load, a boost supply can be placed in series to increase the voltage. While a fixed voltage DC-DC converter can be used as the boost supply, a programmable power supply is preferred to keep the load voltage at the minimum to draw full current as the device under test ramps up in voltage.

For more information on electronic loads, contact AMETEK Programmable Power. You can send e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Power on the Go: Tips on Portable Power Supplies

Written on February 28, 2017 at 11:06 am, by

XBT portable power supplyAlthough power supplies are most often used in a single location, such as a design lab or a factory test station, there are times when portability is desirable. For example, you may not want to purchase a laboratory power supply with sophisticated computer-control features, such as the Sorensen XBT Series (see right), for every design engineer in your company because they may not often need those capabilities. In this case, a good strategy might be to have one that can be shared amongst the design engineers, moving it from bench to bench when needed.

So, what should you look for when purchasing a portable power supply? As simple as it may sound, first look for a handle. As you can see from the picture above, the XBT Series comes with a carrying handle that allows you to easily tote it from one benchtop or test station to another. The handle helps prevent you from accidentally dropping and damaging the power supply. Other features to consider include compact size and light weight. The XBT Series measures just 8.5-in x 5.3-in. X 17-in. and weighs less than 15 pounds. Many other AMETEK Programmable Power products, including the California Instruments Compact i/iX Series AC/DC power source and the Sorensen SG Series DC Power Supplies, can be outfitted with carrying handles.

Portable benchtop instrument caseIf the power supplies that you want to transport do not have carrying handles, you can always make a portable package yourself by using a benchtop instrument case like the one shown at left. This assumes, of course, that the power supplies can be mounted in a 19-in. rack. One advantage of this approach is that if your power supplies do not completely fill the case, you can add other instruments.

To move supplies that may be too big or heavy to simply carry around, you can use a rolling 19-in. rack. These are available from many different manufacturers. When purchasing a rolling rack, consider buying one big enough to not only accommodate the power sources, but also shelves or drawers to hold test accessories that you may also want to cart around with the power supplies. These accessories might include test leads and a copy of the supply’s operating manual.

These are just a couple of tips on how to make programmable power, portable power as well. For more information on portable power supplies, contact AMETEK Programmable Power. You can send an e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Four test bench power supply tricks

Written on February 14, 2017 at 11:42 am, by

Test bench power supplies, like the Sorensen XBT Series, are more than just power supplies. They are versatile test instruments that you can use to make your life simpler. Here are five things that you can do with Sorensen test bench power supplies that just might make your tests more effective.

#1. Connect supplies in series for more output voltage.

The Sorensen XBT provides three separate supplies in a single instruments. Two of the supplies can be programmed to output 0 – 32 VDC at up to 3 A. The third supply can output 0 – 15 VDC, 0 – 5 A, up to a maximum of 30W. But, what can you do if you need to supply 48 VDC to a test circuit?

The answer is to connect the two 32 VDC supplies in series. Because the supplies are isolated from one another, connecting the two supplies in series works like a charm. For best results, set each supply for 50% of the total output voltage and set the current limit of each supply to the maximum that the load can safely handle.

#2. Connect supplies in parallel for more output current.

You can do something similar if your application requires more than the 3 A that a single output of the XBT can provide. Instead of connecting the two supplies in series, however, you connect them in parallel. When connected this way, the XBT can supply up to 6 A at voltages up to 32 VDC. The XBT allows you to set this up via the front panel and connect to a single set of output terminals. This is more convenient than using patch cords to connect supplies in parallel and reduces the opportunity for human error.

#3. Computer control for consistent ramping.

A common thing a design engineer might do with a test bench power supply is ramp up or down a supply voltage to see how a circuit or system works over a range of supply voltages. You could do this manually by simply cranking up or down the voltage control, but if you do this programmatically, you can have the supply output a ramp with a consistent slope. You might also have the computer controlling the supply monitor the circuit or system under test for proper operation, and when it detects some abnormal operation, suspend the ramp and make note of the voltage at which problems started to occur

#4. Computer control for sensor simulation.

Many sensors, such as the TMP35 low-voltage temperature sensor outputs a voltage proportional to the ambient temperature. They are used in a wide variety of applications, including environmental control systems, industrial process control systems, and fire alarms. Generally, temperature sensors like this output 10 mV/°C.

To test circuits and systems that use these sensors, you can use a programmable test bench power supply to simulate the sensor. The temperature profile might be a simple ramp as in tip #3, or a more complicated temperature profile. In either case, you would use the remote control capability of the XBT supply to program the temperature profile.

These are just some of the ways that you can make your test bench power supply jump through hoops. For more information on test bench power supplies and how to use them, contact AMETEK Programmable Power. You can send e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Calculate voltage drop to prevent system problems

Written on January 20, 2017 at 12:24 pm, by

One of the problems we frequently encounter in the field is that power supply users fail to take into account the voltage drop in the wires connecting a power supply to a device under test (DUT) or other electronic system. When a load draws a high current, the voltage drop across the power leads could be high enough to cause a device under test to fail or cause a system to malfunction.

The voltage drop across the power leads is actually very easy to calculate:

E = 2 x I x R

This is basically Ohm’s Law, but because there are two wires that connect the power supply to the load, the voltage drop, E, across the power leads is twice the value you’d normally calculate using Ohm’s Law. I is the current drawn by the device under test or load, and R is the resistance of one of the power leads. When performing this calculation, you should use the maximum current that your DUT or load will draw. That will give you the worst case voltage drop for your system.

Wire Size (AWG) Ω/100 ft. (one-way) Ampacity
14 0.257 15
12 0.162 20
10 0.102 30
8 0.064 40
6 0.043 55
4 0.025 70
2 0.015 95
1/0 0.010 125
3/0 0.006 165

Once you know the maximum current, you then need to figure out the resistance of the power leads. You do this by referring to the table at right. It lists the resistance per 100 ft. for a variety of popular copper wire sizes. To calculate the resistance of your power leads, you divide the length of the leads by 100 and then multiply by the value in the table. For example, the resistance of a 10-ft. length of #12 wire would be 0.162/10 or 0.016 Ω. The ampacity column gives the maximum current value that the given wire size can safely handle.

Let’s look at an example. If your system uses 10-ft., 12-ga. power leads and the load draws 20 A, the voltage drop across the power leads is:

E = 2 x I x R = 2 E = 2 x 20 x (10/100 x 0.162) = 0.65 V

Once you’ve performed this calculation, you can decide whether or not this voltage drop is acceptable in your application. If not, you have several options. You can increase the wire size of the power leads or use a supply that uses remote sensing to compensate for the voltage drop.

Knowing the voltage drop across your power leads will help you achieve better results with your test or electronic system. For more information on this and other power supply topics, contact AMETEK Programmable Power. You can send e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Know your power supply jargon: resolution and accuracy

Written on January 10, 2017 at 7:35 am, by

Two terms that often get bandied about when describing automated test systems are resolution and accuracy. To get the best results from your power supplies, it is important to understand the difference between these two specifications and how they affect your system.

The New Oxford American Dictionary defines resolution as, “the smallest interval measurable by a scientific (especially optical) instrument.” When applied to a voltage source, we can take that definition to mean “the smallest amount of voltage that the output of a voltage source can be changed.”

Now, let’s take a look at what this means in practice. The DC, AC, and AC+DC voltage resolution of AMETEK Programmable Power’s Asterion Series is 0.02 VDC. This means that you can change the output value in 20 mV steps. This fine resolution is more than sufficient for the vast majority of tests that require you to ramp up or ramp down the output voltage.

Accuracy is another story, however. The New Oxford American Dictionary gives the technical definition of accuracy as “the degree to which the result of a measurement, calculation, or specification conforms to the correct value or a standard.” A power supply’s accuracy is a measure of how close the actual output will be to the value to which it is programmed.

The DC accuracy of the Asterion Series is ± (0.1% of actual + 0.2% of full-scale). So, for example, if the output voltage is set to 100 VDC, the actual output voltage could be off by as much as 0.6 VDC (0.1% x 100 VDC + 0.2% x 250 VDC = 0.6 VDC). That means the output voltage could be as low as 99.4 VDC and as high as 100.6 VDC.

In AC and AC+DC modes, other factors also contribute to the accuracy of the output voltage. When the output frequency of the supply is below 1 kHz, the AC accuracy is the same as the DC accuracy. When the frequency of the output voltage is above 1 kHz, however, you must add ±0.2% of full-scale/kHz. When the supply is in AC+DC mode, the output voltage may be off by an additional ±0.1% of full scale.

Knowing the relationship between resolution and accuracy will help you achieve better results with your test system. For more information on power source accuracy and resolution, contact AMETEK Programmable Power. You can send e-mail to sales.ppd@ametek.com or phone 800-733-5427.

Control options abound for Programmable Power products

Written on December 15, 2016 at 7:00 am, by

asterion

Ethernet, USB and RS232 standard control interfaces are standard equipment on the Asterion Series AC/DC power sources, and there is an optional IEEE-488 (GPIB) control interface available.

One of the most common applications for AMETEK Programmable Power power sources is some kind of automatic test system. The California Instruments Asterion AC Series, for example, was designed to be used in commercial and military avionics test system, manufacturing and process control, and IEC standards test systems. It includes Ethernet, USB and RS232 standard control interfaces, and there is an optional IEEE-488 (GPIB) control interface available.

  • RS-232. While RS-232 ports are rarely found on personal computers these days, they are still found on many pieces of test equipment and are a viable option for controlling this equipment. Many industrial computers can still be outfitted with RS-232 ports, and personal computers can be connected to test equipment with RS-232 ports by using a Universal Serial Bus (USB) – RS232 adapter. Disadvantages include the ability to control only one device per port and relatively data rates (less than 20 kbytes/s).
  • Universal Serial Bus (USB). For many applications, engineers now use USB instead of RS232 for serial data connections. USB offers higher data rates than RS232, and you can connect up to 127 devices to a single port. USB links are easy to set up and use, especially in lab applications. If you plan to use a USB device in a factory or an industrial environment, be sure to purchase cables specifically designed for this use.
  • Ethernet LXI. More recently, engineers have begun to use Ethernet to connect test equipment to control computers. Test instruments that have an Ethernet port generally support the LAN eXtensions for Instrumentation, or LXI, standard. This standard is published by the LXI Consortium, a group comprised of all the top test and measurement equipment manufacturers. There are currently more than 3,500 certified LXI products, and that includes the Asterion AC Series, as well as other AMETEK Programmable Power products.
    Because it’s based on Ethernet technology, LXI systems not only offer high data rates, but very impressive connectivity. You can literally connect to instruments anywhere in the world. This makes LXI a good choice for systems where instruments are located far from the control computer, including remote applications.
  • IEEE 488 (GPIB). Designed by Hewlett Packard in the late 1960s, the IEEE 488 bus is arguably the original automatic test bus. Up to 15 instruments can be connected to its eight-bit parallel interface, and it has a maximum data rate on the order of 1 MHz. Despite its relatively low performance and being somewhat difficult to use, many legacy test systems still use the IEEE 488 interface.

In addition to choosing the interface that you’ll use to control your Programmable Power power source, you’ll need to specify an appropriate computer. In the lab, a desktop or laptop computer will work just fine. If your automatic test system is destined for the factory or some other harsh environment, you’ll want to purchase a ruggedized industrial computer. These are made by many different manufacturers and will operate at more extreme temperatures and withstand mechanical shocks and vibrations better than consumer-grade PCs.

For more information on how to use AMETEK Programmable Power’s AC, DC, and AC/DC power sources in automatic test systems, contact AMETEK Programmable Power. You can send e-mail to sales.ppd@ametek.com or phone 800-733-5427.

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 sales.ppd@ametek.com or phone 800-733-5427.