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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.

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 sales.ppd@ametek.com 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.

constant-resistance-mode

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.

constant-voltage-mode

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.

constant-power-mode

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.

power-contour

For more information on electronic loads, contact AMETEK Programmable Power by sending an e-mail to sales.ppd@ametek.com 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.

asterion

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 sales.ppd@ametek.com 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.

sga-analog-voltage-control

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