Posted on 13 March 2020

Power meets Precision




The PX8000 Precision Power Scope is a mixture of power-analyzer and oscilloscope

DLM4000, WT3000, DL850E – Yokogawa’s last year’s developments focused on power measurement in a special way. The new Power Scope PX8000 is supposed to fill a gap in this power measurement solution as it combines power-analyzer and oscilloscope functions.

By Marisa Robles Consée, Corresponding Editor; Bodo’s Power Systems

Johann Mathä considers the PX8000 “a logical consequence of Yokogawa’s measurement roadmap”. Yokogawa Germany’s Marketing Manager elaborates: “We have pulled together power meter and oscilloscope functions into a hybrid instrument, because we believe that this is needed to deal with a growing number of designs that either have to meet increasingly stringent energy-usage regulations or deal with often unpredictable renewable-energy systems.” The PX8000 precisely captures voltage and current waveforms and may be suitable for various applications and solutions for a wide range of emerging power measurement challenges. “With the launch of this instrument, R&D professionals need no longer compromise on the need for high-accuracy time-based power measurement – something that conventional power analyzers and oscilloscopes were never designed to meet”, Mathä states.

The power analyzer PX8000 pulls in scope functions for energy-saving designs

PX8000: Packed like a digital oscilloscope

The PX8000 is packed like a digital oscilloscope and has 12 bit resolution with 100 MSample/s sampling and 20 MHz bandwidth. This means that it can be used for accurate measurement of inverter pulse shapes, which can then be used to fine-tune inverter efficiency. A choice of input modules covers voltage, current, and sensor measurements at voltages up to 1000 VRMS and currents up to 5 ARMS (higher values are possible with external current sensors), with a basic accuracy of ±0.1% of reading.

The PX8000 has built-in functions for the direct calculation of derived parameters, such as RMS and mean power values, to enable the identification of cycle-by-cycle trends. It also supports the capture of power waveforms over specific periods of time through the definition of start and stop “cursors.” This is particularly useful for the examination of transient phenomena and the design of periodically controlled equipment. To ensure that such equipment complies with energy standards, it is vital to measure power consumption across a range of modes, from “sleep” to full activity and all the transient states in between.

The PX8000 is the new fl agship product for Yokogawa’s range of industryproven power analyzers

Fast shifts between operating modes

Clive Davis, manager of test and measurement marketing for Yokogawa in Europe and Africa, says: “The PX8000 has a number of innovative features that support the crucial measurement and analysis of transient power profiles.” For example, the device provides simultaneous voltage and current multiplication to give real-time power sampling. This supports both transient measurement (as standard) and numerical values averaged across the sample period. The available measurement period will depend on the sample rate and the memory size. “People try to use an oscilloscope to measure power because it feels easy. But oscilloscopes are not designed to be temperature stable,” says Davis, leading to problems with drift in measurements. He adds: “A fundamental issue is the transient nature of power. That’s where you need integration between the power meter and oscilloscope, because the conventional oscilloscope isn’t calibrated.” Trend measurements between waveforms can be calculated by mathematical functions (up to four million points). The system provides graphical displays of voltage, current and power readings. The waveforms can be inspected for specific numerical values at any point and averages can be calculated between start and stop cursors. Such capabilities are particularly important when analyzing and optimizing the performance of, for instance, lighting and electric motors at start-up.

“Up to 16 different waveforms – including voltage, current and power – can be displayed side-by-side, giving engineers instant snapshots of performance”, claims Hafeez Najumudeen, Product Marketing Manager for Europe and Africa.

The PX8000 supports the capture of power waveforms over specific periods of time through the definition of start and stop “cursors”. This is particularly useful for examining transient phenomena and in the design of periodically controlled equipment. To ensure that equipment such as photocopiers complies with energy standards, for instance, it is vital to measure power consumption across a range of different modes from “sleep” to full activity – and all the transient states in between. Despite this, for certain tasks it is important to be able to display values on an X-Y axis. Motors, for instance, are characterized by an ST-curve that shows the relationship between speed and torque. The PX8000 supports such displays as standard. It can also display Lissajous waveforms of input and output for phase analysis.

Hafeez Najumudeen says the harmonics analysis is a key component, up to surprisingly high orders, for applications that include power supplies and wireless power chargers, where the inductive energy transfer components can lead to high frequencies being injected into the power signal: “The PX8000 makes it possible to simultaneously measure the harmonic components of voltage and current waves as well as the harmonic distortion factor. Harmonic measurements take place in parallel with conventional voltage and current measurement. Harmonics up to the 500th order of the fundamental can be measured.” Additionally, the system features arithmetical, time-shift, FFT and other computations that enable users to display waveforms with offsets and skew corrections. “Users can also define their own computations via equations that combine differentials, integrals, digital filters and many other functions”, he adds.

Choice of Modules

A choice of input modules covers voltage, current and sensor measurements at voltages up to 1000 VRMS and currents up to 5 ARMS. Higher values are possible with external current sensors. Basic accuracy is down to ±0.1 percent. Sensors can introduce phase errors or skew between the current and voltage inputs. The de-skew kit 701936 enables this phase shift to be corrected automatically for each power measuring element individually. Up to three sensor and voltage measurement modules can be installed.

To prevent incompatibilities, the PX8000 detects mismatched current and voltage modules and flags them with an on-screen warning message. The system also comes with a range of dedicated input connectors designed to prevent incorrect or dangerous power connections. Using these connectors, it is not possible, for instance, to connect a current probe to a voltage input terminal. A tie-wrap system prevents accidental current terminal disconnection.

Clive Davis and Hafeez Jajumudeen: "The harmonics analysis up to surprisingly high orders is a key component."

This new instrument is powered by Yokogawa’s isoPRO technology, which offers isolation performance at the highest speeds. Designed with energy-saving applications in mind, this delivers the performance needed to evaluate high-efficiency inverters that operate at a high voltage, current, and frequency, while achieving the measurement accuracy, stability, and repeatability. Connection to a PC can be established via standard Ethernet/USB/GP-IB connections. The software displays waveforms in a simple and clear graphical style that is familiar to users of Yokogawa’s Xviewer software. Researchers who want to use their own analysis software can use the LabVIEW driver to establish a connection to the PX8000.

Fit for many applications

Applications for the PX8000 cover various areas from renewable power to advanced robotics. Any situation where power consumption is at a premium – which means almost anywhere power is consumed – can benefit from the introduction of its precision measurement and analysis capabilities. Typical applications include inverter and motor testing, reactor loss measurement for inverter boost circuits, transient response measurement for industrial robots, wireless charger efficiency measurement, and voltage and power measurement for electricity distribution systems.

“The vertical resolution of analog/digital conversion is one of the most important factors in precision measurement”, Hafeez Najumudeen says. A common problem when testing inverter motors is the presence of ambient noise that can mean test values are nonzero even before testing begins. The PX8000’s offset capabilities mean such effects can be nullified and specific inputs can be isolated for testing and analysis. Another example is the ability to evaluate motor-driven robots, power consumption of all motors and controllers is measured throughout all operational speeds and action patterns. He adds: “Design engineers need to measure inrush voltage, current and power over the pattern of repeated actions. Efficiency is calculated by comparing mechanical output with input power.” During actual operating conditions, the time to accelerate and decelerate such motors can range from several hundred milliseconds to several seconds. “As a PWM-driven motor rotates from the reset position to top speed, the drive frequency changes from DC to several hundred Hz. The PX8000 gives design engineers insight into power consumption and efficiency throughout a robot’s operational performance.”


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