Accuracy figures quoted in manufacturers’ specifications – and indeed some of the parameters listed in calibration certificates issued by well-established test houses – can be meaningless when tasks are out of context.
Traditionally, AC power meters have been calibrated at frequencies of 50 to 60 Hz. However, the reason that Yokogawa and other power meters are using a higher power measuring bandwidths is that most applications consume power at higher frequencies.
• Switch-mode power supplies
• High-frequency electronic lighting ballasts
• Soft starters in motor control systems
• Frequency converters in traction application
There is a question mark on the validity of the power meter or analyzer.
A power calibration at only 50 or 60Hz has little value
Calibration or high-frequency power is lagged behind the development of power meters to address applications, and a few national laboratories can provide traceability up to 100 kHz: the frequency at which calibrated to provide accurate results in these application sectors. Yokogawa is the only industrial organization (ie non-government or national) to offer this capability.
An ISO 17025 accredited calibration proves the accuracy of a power meter
Quality systems such as ISO 9001 aim at confirming the compliance of the management system to a standard, but do not specifically evaluate the technical competence of a laboratory.
Laboratories that are accredited to ISO 17025, like Yokogawa, have demonstrated that they are technically competent and able to produce precise and accurate calibration measurements, which are globally recognised.
A calibration of only voltage or current has no value
In reality, mains voltage waveforms are not sinusoidal and exhibit a typical flattening of the peaks due to the loading effects of switch mode power supplies etc. on the distribution network. This causes harmonics in the voltage waveform, which in turn leads to higher amounts of power consumed at higher frequencies by an instrument connected to the distribution system.
It is also not sufficient to just calibrate using voltage and current, as phase shift is one of the most critical factors which determine a high bandwidth power meter’s uncertainty. Stand-by power measurement is just one of the high profile applications which require the precise measurement of power at both high frequency and low power factor.
A power measuring instrument should be selected whose accuracy is proven for the frequency range of the application
Yokogawa’s European Calibration Laboratory is the only industrial organization to offer traceability up to 100 kHz, and so is the only power meter manufacturer. Only a Yokogawa Calibration Certificate gives the user trust in their instrument’s measurements.
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