1 Abstract The is a power meter that can measure direct input of 60 mv to 1000 V and 10 μa to 30 A with a high degree of accuracy. To enable it to measure targets ranging from standby power to operating power with high precision, the instrument uses the shunt resistance method of current input. This paper describes the features, architecture, and example characteristics of the PW3335. Ken Sakai Engineering Division 4, Engineering Department I. Introduction The IEC 62301 international standard on standby power measurement, whose first edition was issued in 2005, has been incorporated into separate standards for devices such as household electronics and office equipment in order to provide a consistent definition for standby power. The second edition of the standard, which was issued in 2011, further clarifies the uncertainty of power measured values. This additional clarification was needed because standby power is characterized by extremely small power values, making it impossible to ignore the effects of external sources of error on measured values. Since those sources include power measuring instrument uncertainty, instruments used to measure standby power are expected to add low-current ranges, expand the dynamic range of their circuitry, and improve measurement accuracy, including during lowpower-factor measurement. Since the PW3335 provides current ranges extending from 1 ma to 20 A (with guaranteed accuracy from 10 μa to 30 A), basic measurement accuracy of ±0.15% rdg., power factor effects of ±0.1% f.s. (when PF = 0), and a crest factor of 6 (circuit dynamic range that is 6 times the measurement range), it is ideal for measurement that complies with the IEC 62301 standard. In addition, Hioki provides complimentary PC application software that can create IEC 62301-compliant test reports. II. Overview The PW3335 is an AC/DC power meter that delivers that highest basic measurement accuracy of any power measuring instrument in the same class at ±0.15% rdg. with guaranteed accuracy for voltages of 60 mv to 1000 V and currents from 10 μa to 30 A. In its standard configuration, it also ships with harmonic measurement functionality that complies with the IEC 61000-4-7 international standard on harmonic measurement methods, LAN and RS-232C interfaces that support automated shipping inspections on production lines (except the PW3335-01), and synchronized control functionality that enables simultaneous measurement using multiple instruments. Appearance of the PW3335. In addition, the following additional functions equip the instrument for use in a variety of measurement applications: PW3335-01 with a GP-IB interface PW3335-02 with D/A output functionality PW3335-03 with external current sensor input PW3335-04 with a GP-IB interface, D/A output functionality, and external current sensor input III. Features A. Guaranteed Accuracy From 10 μa to 30 A With Direct Input Because the Power HiTester 3332, a previous Hioki product, was designed exclusively for use with AC currents and detected currents by means of current sensors, values obtained when measuring minute currents on the order of several milliamperes were susceptible to the effects of external noise. By contrast, the PW3335 uses shunt resistance to detect currents so that it can measure targets ranging from current consumption during normal equipment operation to minute currents during standby operation with a high degree of accuracy. By switching between two shunt resistors according to the current being measured, the instrument is capable of dynamic measurement of AC currents ranging from 10 μa to 30 A, enabling a single device to fulfill a variety of power measurement needs. B. High Accuracy and Wideband Performance The IEC 62301 standard defines off mode (power switch in the OFF position), standby mode (waiting for
2 remote control input, etc.), and network mode (with network communications enabled) as low-power modes that include the standby state, with a specific type of current waveform envisioned for each. Non-sine waves and asymmetrical waves Pulses or spikes Waveforms with large crest factors Waveforms with low power factors due to phase difference relative to the voltage waveform The PW3335 delivers the following performance so that it can measure these waveforms at a high level of precision: Sampling frequency of approximately 700 khz The instrument can track changes in waveforms thanks to sampling speed that is at least 9 times faster than Hioki s AC/DC Power HiTester 3334. Basic measurement accuracy of ±0.15% rdg. (At less than 50% of the range, ±0.1% rdg. ±0.05% f.s.) This level of accuracy is the highest of any Hioki instrument in the same class. Frequency band of DC and 0.1 Hz to 100 khz This band gives the instrument measurement capabilities including DC measurement, measurement starting at inverter motor low-speed operation, commercial equipment measurement, and measurement of high-frequency equipment. Power factor effects of ±0.1% f.s. (Internal circuit voltage/current phase difference of ±0.0573 ) This level of performance represents Hioki s most advanced specifications and enables the instrument to be used in no-load (low-power-factor) testing of transformers, motors, and other devices. C. Multiple-Instrument Synchronized Control for a Variety of Multiple-Circuit Measurements The PW3335 provides synchronized control functionality that allows synchronized measurement using up to eight instruments either PW3335s or PW3336s/PW3337s connected in parallel with BNC cables. Among the capabilities enabled by this functionality are measurements that require simultaneity, for example comparisons of differences among individual devices or simultaneous parallel testing on production lines. Hioki s complimentary application software PW Communicator can be used to collect data from up to eight instruments. D. Support for Currents of Up to 5000 A With a Current Sensor (PW3335-03, PW3335-04) When an optional voltage output-type current sensor is connected to the PW3335 s external current sensor input terminal, the instrument can be used to measured large currents in excess of 30 A. The instrument s settings distinguish between two types of sensors: TYPE1 (0.5 V output current sensors such as the Clamp On Sensor 9661) and TYPE2 (2 V output current sensors such as the AC/ DC Current Sensor CT6862). The PW3335 can be used to measure currents of up to 5000 A when using the AC Flexible Current Sensor CT9667 Series (TYPE1). E. Range Control to Increase Measurement Efficiency While the PW3335 provides numerous ranges 8 voltage ranges and 14 current ranges (direct input) its range select function, which skips unused ranges, can be used to reduce the nuisance of switching ranges. In addition, since its auto-range function determines the most appropriate range every cycle (commercial frequency), the instrument can switch to the optimal range quickly. Furthermore, the PW3335 incorporates an auto-range integration function (for current ranges from 0.2 A to 20 A) that was lacking on previous products. This capability can be used to measure the integration value for each used range and the total integration value with guaranteed accuracy, allowing integration value measurement for individual equipment operating states. F. Harmonic Measurement Functionality The PW3335 ships standard with functionality for performing measurement that complies with the IEC 61000-4-7 international standard on harmonic measurement at the commercial power frequencies of 50 Hz/60 Hz. IV. Architecture Fig. 1 provides a block diagram of the PW3335-04. All measurement data is processed digitally by a field programmable gate array (FPGA). Then measurement data is processed by digital control circuitry such as the CPU and output via the instrument s display and various interfaces. A. Voltage and Current Input Circuitry Voltage input circuitry uses differential input, an approach with a proven record in Hioki power meters, and delivers high dielectric strength thanks to its combination of a resistance-type potential divider and isolated devices. Current input circuitry uses a shunt detection design and delivers high dielectric strength by means of redundant isolated devices. A built-in current switching device enables current detection using shunt resistance based on the measurement current, allowing high-precision, dynamic measurement without changing connections. A protective diode consisting of shunt resistors connected in parallel as a measure to protect the circuit against inrush current keeps the instrument s internal circuitry from being damaged, even after input of a current of ±100 A peak (when using the 0.2 A to 20 A range) or ±30 A peak (when using the 1 ma to 100 ma range).
3 1 MΩ U ± 1 MΩ Differential Range LPF ADC Isolator Isolator FPGA CPU Display Key RS-232C I ± Voltage input Current input SW Inverting Range LPF Isolator ADC GP-IB LAN Synchronized control External control BNC Buffer Range LPF ADC D/A output Current sensor Fig. 1. Block diagram (hardware). B. A/D Conversion Circuitry Signals from the voltage input and current input circuitry are amplified so as to reach their respective designated full-scale voltages by range s. Hioki has used a proprietary composite for these range s with the goal of ensuring low drift and wideband performance. After range amplification, the band is limited by a lowpass filter with a cutoff frequency of approximately 450 khz, and the voltage and current signals are simultaneously converted into digital signals by 16-bit, 700 khz A/D converters (ADCs). C. FPGA Fig. 2 provides a simplified block diagram for the FPGA s internal circuitry. Voltage and current waveform data input from the ADCs is sent to calculation units, and all calculations are performed concurrently. This waveform data can be sent directly to D/A output, allowing its use in waveform observation. Like the PW3336/PW3337, the PW3335 utilizes a fully digital approach to zero-cross detection, including for waveform shaping. The FPGA incorporates a digital filter whose cutoff frequency can be set to 100 Hz, 500 Hz, 5 khz, or 100 khz, and by manually configuring this filter based on the amount of distortion in the waveform being measured, the operator can enable accurate zero-cross detection. Voltage and current frequency are measured using the waveform data for zero-cross detection. ADC 16-bit, 700 khz, 3 channels ADC control unit Waveform DAC control unit Waveform shaper Anti-aliasing filter DAC 16-bit, 7 channels Frequency calc. Zero-cross detect PWR calc High-speed active power level Waveform processing (harmonic) Fig. 2. Simplified block diagram of FPGA internal circuitry. CPU D. D/A Output (PW3335-02, PW3335-04) Like the PW3336/PW3337, the PW3335 includes functionality for generating high-speed output of active power levels (high-speed active power level output). Designed to capture rapid load fluctuations, this function, which is implemented by the FPGA, generates D/A output by refreshing the active power level each cycle of the voltage or current selected as the synchronization source. For
4 example, with input of 50 Hz AC, high-speed active power level output would take the form of D/A output refreshed every 20 ms (since 20 ms is the duration of each cycle for that current). The maximum input frequency for which this output is supported is 5 khz (with a cycle of 0.2 ms). In addition, although processing for both voltage and current occurs in software, the instrument can generate level output every cycle for commercial frequencies. To provide backward compatibility with previous products, the output voltage for the PW3335 s level output can be switched between 2 V and 5 V. V. Example Characteristics Figs. 3 through 14 illustrate example characteristics of the PW3335 for reference purposes. Fig. 3. Voltage linearity (DC). VI. Conclusion In the drive to achieve energy savings, it is critical to address equipment with high power consumption and standby power. According to materials published by the Japan Ministry of the Environment, power consumed by devices in the standby state accounts for approximately 5% of total household annual power consumption (approximately 228 kwh), an amount that exceeds even the amount of power consumed by electrically heated toilet seats (which accounts for approximately 3.7% of total consumption [2]. This is a value that cannot be ignored when overall power use worldwide is considered, and the countries and regions of the world have enacted a variety of laws and regulations with the goal of reducing standby power consumption. Going forward, manufacturers are likely to redouble efforts to develop products with lower power consumption during both normal operation and standby operation in order to protect the Earth s environment. Against this backdrop, we expect the PW3335 to continue to be used to develop products that deliver energy-saving performance during both of these modes of operation. Fig. 4. Voltage linearity (AC+DC, 55 Hz). Minoru Nagaya *1, Akira Kodaira *1, Ken-ichi Seki *1 Fig. 5. Current linearity (DC). References [1] M. Nagaya, Power Meter PW3336/PW3337 Series, Hioki Giho, vol. 35, no. 1. pp. 29-34, 2014. (Japanese). [2] The Japan Agency for Natural Resources and Energy, The Reality of energy consumption in households, 2015. [Online]. Available: http://www.enecho.meti.go.jp/category/saving_and_new/saving/ general/actual/index.html. Accessed: Mar. 10, 2015. (Japanese). Fig. 6. Current linearity (AC+DC, 55 Hz). *1 Engineering Division 4, Engineering Department
5 Fig. 7. Active power linearity (DC, voltage fixed). Fig. 11. Frequency characteristics, active power (AC+DC). Fig. 8. Active power linearity (AC+DC, 55 Hz, PF = 1, voltage fixed). Fig. 12. Power factor effects (300 V/100 ma range). Fig. 9. Frequency characteristics, voltage (AC+DC). Fig. 13. Temperature characteristics (DC, 0 input). Fig. 10. Frequency characteristics, current (AC+DC). Fig. 14. Temperature characteristics (55 Hz, f.s. input).
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