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  1. Measurement technologies and meter hardware
    1. Measurement technologies
    2. Classification of off-the-shelf power meters
      1. AC meter
      2. Measuring PSU
      3. Meter modules
      4. Component modules
      5. Built-in meters
    3. Summary of off-the-shelf power meters
    4. Measurement component modules
    5. Basic theory of digital measurements
      1. Physical measurement errors
      2. Time-domain errors
      3. Digital domain errors
  2. Next step: Software-Based Meters and Measurement software

Measurement technologies and meter hardware

This section examines the characteristics and suitability of physical measuring devices suitable for energy measurement in information technology.

This section looks at the equipment used for measurement. The first section looks at the physical principles that are used internally by the different types of meters. The second section provides a classification of the various off-the-shelf measurement products according to their principle of use. The following sections list the complete meters, measurement modules and individual integrated circuits found in the study.

The results of the analysis can be used to support the purchase of ready-made commercial measuring devices. Although the models available for sale and the prices change over time, the analysis identifies various types of devices for which this material can be used in procurement and use. We have also assessed the suitability of the devices for use in a measurement laboratory and with the appropriate software (PowerGoblin).

Measurement technologies

Electrical power and energy measurements are fundamentally based on observing the flow of electrical charge through a system. Instantaneous power is obtained by multiplying voltage and current, while energy consumption is determined by integrating power over time. Consequently, the accuracy of an energy meter depends not only on the quality of the current sensor but also on voltage measurement, timing precision, synchronization, and signal processing.

In practice, most measurement instruments determine energy consumption by measuring current using one of several physical principles. The simplest approach is direct measurement of the voltage drop across a known resistance. Alternative methods exploit the magnetic field generated by electric current, electromagnetic induction, optical effects, or magnetoresistive phenomena.

A less common but sometimes useful approach is indirect energy measurement, where a device is powered from an energy storage element such as a battery or capacitor with known capacity. By measuring the change in stored energy before and after operation, the consumed energy can be estimated. Such methods are generally less precise for dynamic workloads but can be useful for long-duration experiments or isolated systems.

Different sensing technologies exhibit trade-offs in accuracy, bandwidth, isolation, cost, power dissipation, and ease of integration. No single technique is universally optimal, and the selection of measurement technology depends on the characteristics of the system under test.

Technique AC DC Description
Physical sensing principles
Shunt resistor X X The most widely used current measurement technique in low-voltage electronics. Current is measured indirectly from the voltage drop across a precision resistor according to Ohm's law. Shunts provide excellent linearity, bandwidth, and low cost, making them common in integrated power monitors and laboratory instruments. Four-terminal (Kelvin) shunts are often used to minimize contact resistance errors. Maximum continuous current for shunts is typically 66% of the peak max.
Hall-effect sensor X X Measures the magnetic field generated by current flowing through a conductor. Hall sensors provide galvanic isolation and can measure both AC and DC currents without inserting a resistive element into the power path. They are widely used in power supplies, motor drives, and battery management systems.
Fluxgate / zero-flux sensor X X High-precision magnetic sensors that actively compensate for magnetic flux to maintain zero magnetic field in the sensing core. These devices provide excellent accuracy, linearity, and low offset drift, making them common in laboratory-grade power analyzers.
Current transformer (CT) X Uses electromagnetic induction to measure AC current through a transformer core. CTs provide electrical isolation and are suitable for high-current and high-voltage systems but cannot measure DC currents.
Rogowski coil X An air-core coil that measures changing magnetic fields generated by AC currents. Rogowski coils offer very wide bandwidth and do not saturate like iron-core transformers, making them useful for transient measurements and high-current applications.
Fiber-optic current sensor (FOCS) X X Measures magnetic fields through optical phenomena such as the Faraday effect. These sensors provide excellent electrical isolation and immunity to electromagnetic interference, making them suitable for power grid and high-voltage applications.
Magnetoresistive sensor X X Uses changes in resistance caused by magnetic fields. Technologies include AMR (anisotropic), GMR (giant), TMR (tunnel), CMR (colossal), and EMR (extraordinary). These sensors can offer higher sensitivity than Hall sensors and are increasingly used in compact, low-power applications.
Capacitive current sensor X Capacitive current sensors measure electrical current indirectly through the electric field generated by a conductor rather than its magnetic field. These sensors exploit capacitive coupling between conductors and can provide galvanic isolation without requiring direct electrical contact. Capacitive sensing is primarily used in high-voltage applications where conventional current transformers or magnetic sensors may be impractical.
SQUID sensor X X Superconducting Quantum Interference Devices (SQUIDs) are among the most sensitive magnetic sensors currently available and are capable of detecting extremely small magnetic fields generated by minute electrical currents. SQUID sensors exploit quantum mechanical effects in superconducting materials to achieve sensitivity far beyond conventional magnetic sensing technologies.
Calorimetric measurement X X Calorimetric measurement determines energy consumption by measuring the heat dissipated by a device rather than directly measuring electrical quantities. Since nearly all consumed electrical energy is eventually converted into heat, calorimetry can provide an absolute reference measurement independent of the electrical properties of the system under test.
Integrated measurement technologies
Coulomb counter / power monitor IC X Power monitor ICs combine precision analog front-ends, AD-converters, and DSP logic into a single component for measuring voltage, current, power, and energy consumption. Most devices employ an internal or external shunt resistor to measure current and digitally integrate the measured current over time to estimate charge transfer (coulomb counting) or energy consumption. These devices are widely used in battery management systems, mobile devices, embedded systems, and low-power electronics due to their compact size, low cost, and digital interfaces such as I²C or SPI.
Energy metering IC X (X) Specialized devices designed for accurate measurement of electrical parameters in power analyzers and smart electricity meters. Typically combine high-resolution AD-converters with dedicated DSP capabilities for calculating RMS voltage and current, active and reactive power, power factor, and accumulated energy consumption. Generally require external voltage and current sensors, such as shunts, current transformers, or Hall-effect sensors. They are optimized for AC measurements and often support multi-phase power systems, harmonic analysis, and standardized billing applications.
Technique Examples Suitability Downsides
Shunt resistor (#1) TME Low current, low-cost designs Additional resistive load, accuracy of the resistor value, thermal drift
Hall sensor Mouser Low-cost designs Magnetic interference
Fluxgate / zero-flux sensor Hioki, Mouser High accuracy, resolution & bandwidth High sec power consumption, noise
Current transformer TME High voltage & current Saturation, hysteresis, phase shift errors (power and energy meters)
Rogowski coil TME High bandwidth signal Requires integrator circuit
Fiber-optic current sensor ABB Power grid Size, price
Magneto-resistive current sensor Digikey Non-linear behavior, thermal drift, sensitive to external fields
Coulomb counter / power monitor IC TI Batteries, mobile devices, embedded systems Limited range, calibration required
Energy metering IC Smart meters, power analyzers Requires external sensors
Capacitive current sensor High voltage Limited applicability to low-voltage systems, specialized
SQUID sensor Ultra-low current measurement Cryogenic cooling
Calorimetric measurement Absolute validation Slow, complex

Classification of off-the-shelf power meters

In the study of measurement equipment, the meters were classified into the following categories:

  1. AC meters
  2. Measuring power supply units (PSU) with integrated measurement
  3. Meter modules requiring an external PSU
    • DC supply connected meter
    • USB power meter
  4. Component modules (circuit boards. ICs) and
  5. Built-in meters

AC meter

An AC meter is the simplest to use - the meter is connected between the power outlet and the device to be measured, either with the electricity passing through the meter or with the meter mounted around the power cable (possible to install without shutting down the device). An AC meter is also suitable, for example, for data centers where complex or custom wiring is not possible. AC metering is very suitable for measuring a wide range of equipment, as most IT devices can be supplied with AC power (even battery powered devices). There are also special AC meters for very high voltage and current environments such as power grids. There is a wide selection of measurement technologies for AC.

AC meters need to support measurement over a relatively wide range of currents, as the consumption of devices and equipment differs significantly. Low-cost AC meters may not be able to measure the highest power devices and may have other sorts of limitations. For example, the power factor of the switching power supplies makes the measuring less straightforward compared to purely resistive loads, the different capacitor stages in the system behave as a buffers, adding latency and smoothness to the results. The measurement focuses on the total consumption of the whole system, which also makes it more difficult to pinpoint smaller subsystems as the sources of consumption. Low-cost AC meters might also have other limitations in their design such as relatively long sampling periods, inaccurate internal clocks and readings, and inaccuracies and other limitations in data export.

Different types of AC meters are widely used and with the proliferation of smart home technology, many AC meters for different smart home ecosystems are available from different home electronics stores. Many IT devices fit within the specifications of these meters, but they often have limited temporal granularity and accuracy of the measurement (e.g. several minutes to hours). Their software ecosystems might also be geared towards instant or periodic monitoring, but not accurate logging of the numeric data for the needs of a systematic measurement process. They even might not contain the functionality for accessing the logged data or exporting the data in a clearly documented format.

Measuring PSU

A measuring power supply unit (PSU) or a laboratory PSU is a power supply with an intermittent current measurement. We identified several laboratory power supplies during the study, but excluded them from the acquisition of lab equipment because the cost of these power supplies can become relatively high, especially as the number of devices to be compared increases. Measuring PSUs are suitable for special applications where high accuracy is required and high manufacturing quality is valued. For general purpose "background" current measurement, their cost may be too high and their use is limited to the measurement of a single or just few DC circuits. Their voltage range usually also covers the majority of digital devices, but the smaller models might not provide enough current to larger IT systems.

Meter modules

Another versatile type of meter, apart from AC current measurement, are meter modules requiring an external PSU. We studied several types of such meters and classified them based on their applicability for the project. The suitability of the meters was assessed on the basis of voltage and current ranges, accuracy, sample rate, price, and the ease of data collection. In practice, some lab power supplies are also sold as separate PSU and meter modules. There are roughly two types of meters. A DC supply connected meter can be set up to provide one or more channels with different voltage levels to the devices to be measured. The meter channels the power from its own power supply. Some of these meters are powered by standard "brick" power supplies, similar to those used for powering e.g. notebook computers. The meters' output voltage range covers a very wide range of devices to be measured, but is typically slightly smaller than that of laboratory power supplies. To simplify the design, these meters often do not perform DC-DC conversion, and the output voltage range extends to just below the input voltage.

Another common type of meter is the USB power meter, which similarly channels the power and data from the USB bus to the device or devices to be measured. The meter can also provide power from an external PSU instead, but the USB input is usually needed for passing through the data (bidirectional). The USB bus itself also provides a crude method for defining power budgets of devices. The USB power meter is limited to devices equipped with a USB bus, but on the other hand, especially with EU legislation and guidelines, USB has become more common as a general purpose power connector, especially for battery-powered devices. The main challenge for USB is that the latest USB charging and power delivery standards have made USB power distribution more complex, which means that not all USB-based meters are able to measure all new USB devices.


Component modules

There is also a category of component modules which includes both integrated circuits (IC, single components) and circuit boards capable of measuring power. We have excluded simple analog devices such as Hall sensors from this category since they require a number of external components (e.g. ADC, MCU, stable power supply, calibration and temperature compensation circuits) for building a meter. These modules offer a modern alternative to building custom power meters from scratch and avoid time-consuming steps such as circuit design. The integrated circuits also have a very small footprint and often provide integrated digital output which simplifies the reading of data. The combination of such chips and high precision components such as shunt resistors can lead to high quality designs comparable to high-end commercial products.

In the study we identified evaluation boards and circuit boards offered as popular DIY kits, and different types of integrated circuits that come factory calibrated with various logic for reducing noise, voltage and temperature compensation, among other features. During the study, we did an initial search for such component modules from the inventories of popular DIY maker manufacturers such as Adafruit, Seeed Studio, and the Raspberry and Arduino related maker companies. We also went through the catalogs of popular component distributors such as Farnell and Digikey. We then used "snowballing" approach by identifying the ICs and techniques used for measurements and searched for other manufacturers offering products based on the same or similar components listed in the chip makers' product catalogs.

Manufacturers often offer different variations of integrated circuits for different applications. Typical ways of classifying circuits are their operating principle, output format (digital, analog), quantity to be measured (voltage, current, etc.), measurement accuracy, voltage and current ranges, need for additional components (separate inductor, resistor, etc.) or price. For example, Texas Instruments provides the following graph for classifying the devices based on their maximum handling capacity of common mode voltage, the measurement accuracy, and type of meter (analog out, digital, integrated comparator, integrated shunt).

Built-in meters

In addition to the above, many digital devices such as computers and computer components have built-in current meters that provide a software-based API for performing voltage, current, power, and energy measurements. Depending on the system, measurements can be done on a component-by-component basis (e.g. processor, graphics card, solid-state disks, USB devices, screen's backlight) or for the whole system (e.g. total instantaneous power consumption of a laptop).

We plan to publish separate documents on the software-based use of built-in meters at a later stage.

Summary of off-the-shelf power meters

The purpose of the study was to identify available solutions for measuring software power usage in general purpose applications, as well as available commercially available metering hardware that can be utilized without extensive prior knowledge of power measurements. As the cost of precision instruments can be relatively high, especially for small purchases, we have limited our focus to products with a unit price below €100 per channel. The idea of channel-specific refinement is to compensate for possible savings when measuring systems with multiple devices.

After mapping the different types of meters, we found out what different off-the-shelf meters and measurement modules are openly available on the market that can be acquired for in-house use. We used the following criteria:

  • The meter is suitable for measuring the consumption of one or more systems selected for the study.
  • The meter measures current, power and/or energy, or its output values can be used to derive a value for energy consumption over some period of time.
  • The total consumption can be accurately broken down between two time points.
  • no PCB design, soldering or other similar equipment manufacturing process is required to implement the meter.
  • Meter output values are readable by software and standard protocols (software & hardware, e.g. SCPI), digital output.
  • To ensure the scope of the meter mapping work, the price per device is limited to €100 per channel.
Name Price Volt Amp Chan Sample rate Proto Target Accuracy Other
Hardkernel
ODROID SmartPower 3 <50€ 3 - 18 3A 2 200 Hz USB TTY MA documented ascii protocol
ODROID SmartPower 2 - - - 1 - - Discontinued
ODROID SmartPower - - - 1 - - Discontinued
Smaller vendors
Joy-IT JT-UM25C 100€ 24V 5A 1 500 Hz BT M protocol not documented
Powerwerx PWRcheck+ 250€ 60V 40A 1 ? USB TTY MNAL protocol not documented, out of stock
VectorFlux ZS-1100-A <750€ 6V (!) 1,5A (!) 1 1 MHz USB - out of stock
VectorFlux ZS-2102-A <750€ 6V (!) 1A (!) 1 1 MHz USB - out of stock
Qoitech Otii Arc Pro 850€ 5V (!) 5A 1 4 kHz USB M protocol not documented
Qoitech Otii Ace Pro 1500€ 25V 5A 1 50 ksps USB MnA protocol not documented
Joulescope 1300€ 15V 3A 1 250 ksps USB MA protocol not documented
Sistemi P1125 <2300€ 1.8 - 8.2 (!) 3.2A 1 10 kHz USB M Discontinued
Sistemi P1150 1000€ 17V 3.2A 1 125 ksps USB MA Not available yet
Lab power supplies
Owon
OWON SPS series 61/31V 5.1/8.1A 1 USB MnA SCPI protocol
OWON SPM series 60/30V 10/5A 1 USB MNAl SCPI protocol
OWON SPE series <200€ 60/30V 10A 1 USB MNAl SCPI protocol
OWON SP series 60/30V 10A 1 TTY MNAl SCPI protocol
OWON P4000 series 60/30V 3/5A 1 TTY MnA SCPI protocol
OWON ODP3032 30V 3A 2 USB,TTY MA SCPI protocol
OWON ODP3063 30+30+6V 6+6+3A 3 USB,LAN,TTY MA SCPI protocol
OWON ODP6033 60+60+6V 3+3+3A 3 USB,LAN,TTY MA SCPI protocol
OWON ODP3122 30+6V 12+3A 2 USB,LAN,TTY MA SCPI protocol
OWON ODP6062 60+6V 6+3A 2 USB,LAN,TTY MA SCPI protocol
Peaktech
PeakTech P 1565 450€ 16V 40A 1 USB MAl protocol not documented
PeakTech P 1570 650€ 16V 60A 1 USB MAL protocol not documented
PeakTech P 1575 450€ 32V 20A 1 USB MNAl protocol not documented
PeakTech P 1575 450€ 32V 20A 1 USB MNAl protocol not documented
PeakTech P 1585 650€ 32V 30A 1 USB MNAl protocol not documented
Rigol
Rigol DP711 350€ 30V 5A 1 TTY MnA SCPI protocol
Rigol DP712 350€ 30V 5A 1 TTY MnA SCPI protocol
Rigol DP811 700€ 40/20V 5/10A 1 USB,LAN MNAl SCPI protocol
Rigol DP811A 850€ 40/20V 5/10A 1 USB,LAN MNAl SCPI protocol
Rigol DP821 700€ 60+8V 1+10A 2 USB,LAN M SCPI protocol
Rigol DP821A 800€ 60+8V 1+10A 2 USB,LAN M SCPI protocol
Rigol DP813 750€ 20/8V 10/20A 2 USB,LAN MNAl SCPI protocol
Rigol DP813A 900€ 20/8V 10/20A 1 USB,LAN MNAl SCPI protocol
Rigol DP822 750€ 20+16V 5+16A 2 USB,LAN MnAl SCPI protocol
Rigol DP822A 900€ 20+5V 5+16A 2 USB,LAN MnA SCPI protocol
Rigol DP831 500€ 30+30+8V 2+2+5A 3 USB,LAN,TTY Ma SCPI protocol
Rigol DP831A 750€ 30+30+8V 2+2+5A 3 USB,LAN Ma SCPI protocol
Rigol DP832 400€ 30+30+5V 3A 3 USB,LAN,TTY MnA SCPI protocol
Rigol DP832A 600€ 30+30+6V 2+2+5A 3 USB,LAN Ma SCPI protocol
Rigol DP932E 550€ 30+30+6V 2+2+5A 3 USB,LAN Ma SCPI protocol
Rigol DP932U 650€ 32+32+6V 3A 3 USB,LAN MnA SCPI protocol
Rigol DP932A 850€ 32+32+6V 3A 3 USB,LAN MnA SCPI protocol
Rigol DP2031 1350€ 32+32+6V 3+3+5A 3 USB,LAN MnA SCPI protocol
Joy-IT
Joy-IT PS360-C 200€ 60V 6A 1 USB MnA protocol not documented
Joy-IT PS1440-C 400€ 60V 24A 1 USB MNAl protocol not documented
Joy-IT RD6012-C 200€ 60V 12A 1 USB MNAl protocol not documented
Joy-IT RD6006-C 300€ 60V 6A 1 USB MnA protocol not documented
Twintex
Twintex PPA100-40A 40.5V 10.2A 1 USB,LAN MNAl
Twintex DSP-1520 15V 20A 1 USB MNAl
Twintex DSP-3210 32V 10A 1 USB MNAl
Twintex PPS-1560 32V 10A 1 TTY MNAl SCPI protocol
Twintex PPS-1560 15.5V 60.5A 1 TTY MNAL SCPI protocol
Twintex PPM-1820 19V 21A 1 TTY MNAl SCPI protocol
Twintex TPM-2010E 20V 10A 1 USB MNAl SCPI protocol
Twintex PPW-2045 20.5V 45.5A 1 TTY MNAL SCPI protocol
Circuit board kits
Adafruit
Adafruit INA260 <10€ 36V 15A 1 I2C MNAl
Adafruit INA228 <15€ 85V 10A 1 I2C MNAl
Adafruit INA3221 <15€ 26V 3.2A 3 I2C MnA
Adafruit INA219 <10€ 26V 3.2A 1 I2C MnA
Adafruit INA169 <10€ 2.7 - 60 5A 1 Analog MnA Analog output only
Adafruit USB Power Gauge <10€ - - - - - Discontinued
Nordic Semi
Nordic Semi Power Profiler Kit II 100€ 5V (!) 1A (!) 1 100 kHz USB -
Nordic Semi NRF6707 - - - 1 - - Discontinued
Smaller vendors
Joy-IT SBC-DVA 48V 8A 1 I2C MnA IC not documented
Curious Electric ISL28022 60V 32A 1 I2C MnA IC not documented
NCD PR3-6 - 5A 8 I2C - Only voltage/current

Description of categories:

  • Price: Retail price for a single unit
  • Type: Type of inputs/outputs. DC = general purpose DC meter
  • Volt: Supported voltage levels. Not all meters support voltage ranges down to 0 Volts.
  • Amp: Maximum sustained current for measurements.
  • Chan: Number of channels for measurements
  • Sample rate: How many samples can be collected per second. Low (< 1 kHz), medium ( 1 < x < 100 kHz), high (> 100 kHz)
  • Proto: Supported hw/sw protocols for communicates with the meter
  • Target: Suitable target devices (SUT) that can be measured with the meter:
    • Mobile (5V, >3A), Notebook (20V, >10A), Large computer (12V, >50A), **A **ccessories (12V, >3A)
    • m/n/l/a = limited support for this category of devices (5V, >2A) (20V, >3A) (12V, > 10A) (12V, >2A)

Measurement component modules

There are also different kinds of power measurement ICs and circuit boards available as building blocks for the Arduino / Raspberry Pi maker community.

Examples of IC vendors:

Basic theory of digital measurements

Physical measurement errors

  • shunt resistor value offset
  • shunt resistor temperature and current dependence
  • amplifier input offset voltage
  • ADC errors
    • DNL
    • INL
    • Gain error
    • Offset error
    • Quantization error
    • Clipping
    • Noise
  • Reference errors

Time-domain errors

  • Attenuation at higher frequencies
  • Simultaneity and sampling jitter
  • Aliasing

Digital domain errors

Next step: Software-Based Meters and Measurement software

The next analysis section covers the Software-Based Meters and Measurement software.