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Choose the Right Gauge Wire for Your Application

Written on June 8, 2017 at 12:26 pm, by

When installing an AMETEK Programmable Power power source, you must properly size the wires you use to connect the AC input power to the power source and the AC or DC output to the load. Selecting the right size wire will ensure that your power source will operate efficiently and reliably.

The tables below will help you determine the appropriate wire size for both the input and output connections. Table 1 gives minimum recommended wire size for copper wire operating at a maximum of 30° C ambient temperature. The data in this table comes from the National Electrical Code, and is for reference only. Local codes can impose different requirements, so make sure to check them before making a final installation. To handle higher currents, wires can be paralleled; refer to the National Electrical Code for guidelines.

Table 1.

There are two main reasons for choosing the right size wire for the load. The first reason is to ensure that the cable can safely carry the maximum load current without overheating, which may present a fire hazard or cause the insulation to degrade. The second reason is to minimize the IR voltage drop across the cable. Both of these phenomena have a direct effect on the quality of power delivered to and from the power source and corresponding loads.

If the ambient temperature of the installation is greater than 30° C, consider using a larger gauge wire than shown in Table 1. The ability of a wire to carry current, also called its ampacity, decreases as the ambient temperature increases. So, use short cables with a larger gauge wire than shown in Table 1. And, if power cables are to be bundled with other cables, you may have to derate even further, as the operating temperature inside the bundle may be higher than the ambient temperature.

Also, be careful when using published commercial utility wiring codes. These codes are designed for the internal wiring of homes and buildings, and while they do take into account safety factors, such as wiring loss, heat, breakdown insulation, and aging, they allow a voltage drop of 5%. Such a high voltage drop may not be acceptable in your application.

In high performance applications where loads draw high inrush or transient currents, make sure to consider the peak currents that the cables may have to accommodate. These peak currents may be up to five times the RMS current values. An underrated wire gauge adds losses, which alter the inrush characteristics of the application and thus the expected performance.

Table 2 shows the ampacity, resistance per 100 ft, and voltage drop per 100 ft. at the rated current, at an ambient temperature of 20° C. Copper wire has a temperature coefficient of α = 0.00393Ω/°C at t1 = 20°C, so that at an elevated temperature, t2, the resistance would be R2 = R1 (1 + α (t2 – t1)).

Table 2.

The output power cables must be large enough to prevent the line voltage drop (the sum of the voltage drops across both output wires) between the power source and the load from exceeding the remote sense capability of the power source. Calculate the voltage drop using the following formula: Voltage Drop = 2 × distance-in-feet × cable-resistance-per-foot × current.

For more information on right gauge wire for your application, contact AMETEK Programmable Power. You can send an e-mail to or phone 800-733-5427.

Ensure Avionics Reliability with MIL-STD-704 Tests

Written on June 8, 2017 at 12:20 pm, by

To ensure that aircraft electronics and other electrically-powered equipment will operate reliably once in the air, you must test them under extreme power conditions. In the military world, MIL-STD-704 (now up to rev. F), “Aircraft Electric Power Characteristics,” establishes the requirements and characteristics of aircraft electric power. This standard is not only used by the U.S. military and military contractors, but has also been adopted, either directly or indirectly, worldwide. For example, the Chinese standard, GJB 181, Characteristics of aircraft electrical power supplies and requirements for utilization equipment, is largely based on MIL-STD-704.

MIL-STD-704 actually defines the power characteristics of an aircraft electric power system, not the test requirements. Section 5.2, for example, describes AC power characteristics. 5.2.1 says, “AC systems shall provide electrical power using single-phase or three-phase wire-connected grounded neutral systems. The voltage waveform shall be a sine wave with a nominal voltage of 115/200 volts and a nominal frequency of 400 Hz.” It also describe three alternative power systems, including a variable frequency system, a double-voltage system and a single-phase, 60 Hz system. Section 5.2 goes on to describe the phase sequence for three-phase systems, normal operation, abnormal operation, and emergency operation characteristics. A series of tables lists the specifications.

Even though we call the tests performed to ensure that equipment will perform properly on board an aircraft “MIL-STD-704 tests,” the standard does not describe any tests. For guidance on testing, there is a series of handbooks that specify tests for different types of input power. These include:

  • MIL-HDBK-704-1, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics

  • MIL-HDBK-704-2, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, 400 Hz, 115 Volt

  • MIL-HDBK-704-3, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Three Phase, 400 Hz, 115 Volt

  • MIL-HDBK-704-4, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, Variable Frequency, 115 Volt

  • MIL-HDBK-704-5, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Three Phase, Variable Frequency, 115 Volt

  • MIL-HDBK-704-6, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, Single Phase, 60 Hz, 115 Volt

  • MIL-HDBK-704-7, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, 270 VDC

  • MIL-HDBK-704-8, Guidance for Test Procedures for Demonstration of Utilization Equipment Compliance to Aircraft Electrical Power Characteristics, 28 VDC

These documents, including MIL-STD-704 (revisions A through F) are available online at EverySpec.Com. For information on how to use AMETEK power sources to run MIL-STD-704, contact AMETEK Programmable Power. You can send an e-mail to or phone 800-733-5427.

Modern Power Supplies Help Reduce Test Costs

Written on May 24, 2017 at 7:57 am, by

Test costs can add considerably to overall manufacturing costs, especially when extensive testing is required. That’s why it’s important to keep test costs to a minimum. Reduced test costs translate to lower manufacturing costs. Modern power supplies, such as California Instruments’ Asterion Series, have several features that can help you reduce test costs:

Faster command processing times
Because modern power supplies use more sophisticated processors, they can process commands faster than earlier generations of power supplies. Reducing command processing times means reduced test times, and that helps lower test costs.

Command processing times are not often specified for power supplies, but there is a test that you can perform to compare the command processing times of different power supplies. What you do is program a power supply to go from 0 V to some particular value and measure the time from the point at which you send the command to the time the power supply voltage reaches the target value.

While this test is not measuring just the command processing time, it will allow you to compare the performance of several different power supplies. Perform a similar test for other commands and you can get a better feel for how the power supply will perform in your application.

Built-in measurement capabilities
Built-in measurement capabilities can also help you shave test times. Communicating with a single instrument, such as a power supply with measurement capabilities, instead of multiple instruments, such as a power supply and system DMM, can save overall test time. An added benefit of using a power source with measurement capability is that the test system design is simpler, and because you’re using fewer instruments and less cabling, the test system should be more reliable, too.

Advanced software commands
Many tests require a power supply to step through a series of different outputs during the test. While it is possible to program each of these steps individually from the control computer, a much more efficient and time-saving way is by using what’s commonly called the list function.

Too see how this works, refer to Figure 1. It shows a typical series of output voltages that you might generate using the list function. It includes three different AC voltage steps: 160 volts for 33 milliseconds, 120 volts for 83 ms, and 80 volts for 150 ms, separated by three intervals of zero volts for 67 ms. The list specifies the pulses as three voltage points (point 0, 2, and 4), each with its corresponding dwell points. The intervals are three zero-voltage points (point 1, 3, and 5) of equal time duration. In addition to the different output voltages, you can also set a count parameter, which specifies how many times the power supply will output the sequence.

Figure 1.

The point here is that you set up this sequence with a single command instead of a series of commands, and by doing so, you save test time.

These are just three ways that modern power supplies help you reduce test costs. For more information on how AMETEK power supplies help you reduce test, contact AMETEK Programmable Power. You can send an e-mail to or phone 800-733-5427.

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 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  Information also is available from an authorized AMETEK Programmable Power sales representative, who can be located by visiting

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

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 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 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 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 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 or phone 800-733-5427.