Measurements of DC power can reveal a great deal about a system or its components. Power consumption is a global concern, and DC measurements, depending upon the choice of test equipment, can provide important details about the components that handle DC power within an electronic system, such as AC-to-DC converters, DC-to-DC converters, DC to AC converter, DC loads, inverters, and power supplies. The levels of DC power that often must be measured can range from milliwatts in portable electronic devices to thousands of watts produced by DC power generators and power supplies. While it is possible to determine power by measuring DC current and voltage with a voltmeter, modern test tools can make the task much easier by automatically measuring DC current and voltage over multiple channels and accurately calculating DC power.
Obtaining the best test tools for DC power measurements involves knowing something about the type of DC power source or load to be tested, such as an analog power supply, switch-mode power supply (SMPS), or DC-to-DC converter. Knowing the types of power levels and duty cycle at which they are to be tested is also helpful, since longer-duration measurements may require test equipment with longer memory to capture a larger number of measurements over a longer duration.
One parameter often applied to DC power supplies is safe operating area (SOA), which is a measure of voltage versus current to determine how much power a given supply will provide with changing loads, changes in operating temperature, and other changes in environmental conditions. Additional DC power measurements typically involve characterizing the quality of the DC power, such as its stability, transient response, and noise levels. Different types of test instruments are available for characterizing DC power in different ways.
Traditionally, oscilloscopes have been dependable test tools for measuring DC power, with separate oscilloscope channels required for measuring simultaneous DC current using a current probe, and voltage. Power analyzers can more conveniently measure voltage, current, and power, typically at higher levels than an oscilloscope, using dedicated test ports for current and voltage measurements. The Yokogawa WT1800 high-performance power analyzer is an example of such an instrument, with as many as six channels each with current and voltage connections. It offers direct input ranges of 10 mA to 5 A or 1 to 50 A for current and 1.5 to 1000.0 V for voltage. With 3-dB measurement bandwidth as wide as 5 MHz, 2 MSamples/s sampling rate, and 16-b precision, it offers basic measurement accuracy of ±0.1%. Operation is simplified by many automatic functions; the power analyzer even has an operator’s manual stored in internal memory when needed.
When higher accuracy is required, Yokogawa’s model WT3000 power analyzer features improved basic measurement accuracy of ±0.02%. It has two less measurement channels, each with current and voltage connections and bandwidths from 0.1 Hz to 1 MHz. The WT3000 has maximum current range as high as 30 A and maximum voltage range to 1000 V. With data update rates as fast as 50 ms, it can analyze transient and rapidly changing events.
When only the highest accuracy will do, Yokogawa’s model WT3000e power analyzer boasts basic measurement accuracy within ±0.01% of a reading. It also features measurement bandwidths of 0.1 Hz to 1 MHz. All three Yokogawa power analyzers include many automatic test functions for ease of use and highly visible 8.4-in. liquid-crystal-display (LCD) screens for quick, efficient analysis of results.
Measuring DC power may require monitoring and recording fluctuations in a supply line due to over and under voltages, transients, and harmonics, in which case a power quality analyzer may provide more detail than a power analyzer, although typically at lower current, voltage, and DC power levels. The Hioki 3196 power quality analyzer is an example of such an instrument, capable of providing real-time analysis of voltage, current, and power and short-term fluctuations. It can be used to test a number of different systems, including single-phase/two-wire, single-phase/three-wire, three-phase/three-wire, and three-phase/four-wire systems. The power quality analyzer provides as much as 16-b precision and can perform measurements of a variety of power quality parameters, including power factor, displacement power factor, voltage unbalance factor, and current unbalance factor.
These instruments represent just a sampling of the DC power measurement solutions available on the Axiom web site. For further options, click on the links to “Electrical Test and Power Analyzers” for an extensive listing of power analyzers for rent and downloadable data sheets with additional information on each instrument.