DC and AC measurements

Our services

Instruments for measuring low-frequency (LF) electrical quantities are traditionally present in all segments related to electricity; they are used for education purposes in schools, they are indispensable in repair workshops, they are needed in production lines maintenance as well as in the R&D in all electrotechnical laboratories. Moreover, testing and especially calibration laboratories essentially depend on them.

Development of low-frequency instruments started in 19th centuries when pioneers like Michael Faraday, Edward Weston, Elihu Thomson et al. invented first galvanometers, voltameters and amperemeters to experiment, measure and study new and yet not well-known phenomena related to electromagnetics and electricity. A significant progress in science and technology and later in industry also triggered a rapid development in complexity as well as in precision of measuring equipment which is today present in kinds of industry like power electronic manufacturing, transportation, medicine, automotive, electronics development, machinery industries, etc. Nowadays, inexpensive handheld instruments measuring AC and DC current andvoltage, resistance, etc. with accuracy typically well below 1% are readily used. Furthermore, the instruments like HP/Agilent/Keysight 3458A, Fluke 8588A reference multimeters, Zener-based DC voltage standards, Fluke 5790A AC measurement standard, and reference shunt resistors are used when higher accuracy in a part-per-million scale is needed for precise measurements in R&D and in calibration laboratories or even to provide measurement traceability to the primary unit definition. In addition, a novel Josephson effect-based standards are used in metrology laboratories to provide state-of-the-art accuracy which typically ranges in parts-per-1010.

On contrary, the instruments for measuring of RF&MW and especially EMC phenomena are relatively new. Additionally, all physical phenomena’s, parameters and conditions influencing the measurements are not yet very well-known and are often difficult to control, therefore this equipment is generally more expensive and bring typically significantly higher uncertainty which sometimes exceeds 10%.

SIQ provides a broad scope of AC and DC calibration services for almost all types of LF instruments used in different type of industries. Calibrations are usually performed at SIQ or when required also at the customer’s premises (on-site). We perform accredited calibration of the following AC and DC quantities:

  • DC voltage up to 1000 V
  • DC current from 1 pA to 1500 A
  • DC resistance up to 100 TΩ
  • DC power up to 20 kW
  • DC current up to 3 kA using current clamps, current transformers, or current transducers
  • AC voltage up to 1000 V (from 10 Hz to 1 MHz)
  • AC current from 1 μA to 100 A (from 10 Hz to 30 kHz)
  • AC power up to 70 kVA (from 45 Hz to 850 Hz)
  • Phase from 0° to 360° (from 10 Hz to 1 kHz)
  • AC current up to 3 kA using current clamps, current transformers, or current transducers (from 45 Hz to 450 Hz)
  • individual harmonic components, interharmonics, total harmonic distortion (THD) and flicker, dips, and swells

Calibration of AC/DC test equipment at SIQ

Universal multimeters, DMMs

Universal multimeters are calibrated at:

  • direct and alternating voltage
  • direct and alternating current
  • resistance, capacitance, and frequency

Universal calibrators

The standard calibration parameters are:

We also calibrate oscilloscope’s SCOPE option:

  • AC and DC voltage
  • square wave
  • fast edge
  • leveled sinewave
  • time marker
  • wave generator

Before calibration, 24 hours preheating is required.

AC measurement standard

The AC measuring standards (e.g., Fluke 5790A) are extremely accurate AC meters (e.g., measuring range from 2.2 mV to 1000 V in the frequency range from 10 Hz to 1 MHz with a manufacturer’s specification of 24 ppm). Please note that exact frequency range depends on amplitude range.

Calibration parameters:

  • direct voltage
  • AC/DC transfer
  • wideband input AC accuracy
  • wideband input impedance

Estimated calibration time is approximately 14 days.

Meters (μΩ-, mΩ-, Ω-meters), resistance simulators (RTD, calibrators), standard resistors, resistors, high-ohm resistance decades, shunts, etc.

We calibrate direct resistance as well as an impedance at different frequencies.

Calibration of a direct resistance or a direct current is performed by measuring voltage drop on the standard resistor or by using zero-flux system. The measuring currents are usually higher when calibration lower resistances (above 1 A or even over 100 A).

Simultaneously we calibrate the measurement time by a comparison method, and we calibrate different measurement currents directly or by measuring a voltage drop on standard resistors. High-ohms resistors are calibrated at different voltages.

Voltage sources and electronic loads

Calibration parameters of voltage sources are:

  • AC or DC current
  • ripple and noise (presence of AC component at DC generated voltage)
  • stability due to variations in supply voltage
  • stability due to change of the load (output loaded with different power resistors)

Calibration parameters of electronic load:

  • voltage
  • current and
  • power

Current clamps (coils, sensors, transducers), current and voltage transformers

According to operation principle we distinguish two types of current transducers and clamps:

  • Hall effect principle and
  • Rogowski coils, which operate on Faraday’s induction law when measuring electric current.

Higher currents can be generated directly or over a specified number of turns.  On calibration certificate we unambiguously mark serial numbers of clamps, measurement channel number and other settings when clamps, coils or transducers are included in the measuring system.

Alternating and direct power meters

Calibration parameters of power meters:

  • AC/DC voltage and current
  • DC and AC power (The power can be measured directly or by using     associated clamps, coils, or transducers)
  • power factor (PF) at positive and/or negative phase between voltage and current
  • frequency
  • harmonic distortions for current and voltage signals
  • other parameters (torque, revolution-RPM…)

Typically, we calibrate all channels. It is important that the corresponding measuring equipment is used on the same channels and using the same settings as during calibration.

PQ analyzers, installation meters, network parameter meters

Calibration parameters for network quality analyzers are:

  • AC voltage and current (measured directly or via associated coils)
  • PQ parameters (THD or total harmonic distortion, individual harmonic components, flickers, interharmonics, dip/swell)
  • alternating power
  • phase 0° to 360°
  • other parameters related to network quality

The main calibration parameters for installation meters are:

  • DC and/or AC voltage
  • insulation resistance
  • insulation voltage (IR)
  • measuring current
  • ground resistance
  • RCD times
  • RCD circuit currents
  • impedance (absolute and relative measurement)

Other calibrated parameters:

  • short circuit current
  • open circuit voltage
  • different measuring currents
  • low resistance

Calibration is carried out at 50 Hz and/or 60 Hz.

Other measuring instruments

In addition to instruments listed above we also calibrate:

  • measuring circuits (frequency characteristics)
  • different types of digital and analogue multimeters
  • AC and DC voltmeters
  • nanovoltmeters, followed by amperemeters and nano and micro amperemeters
  • different resistance calibrators, generators, or simulators
  • high-ohm and low-ohm decades
  • resistance of resistors and shunts measured at different currents
  • chargers
  • battery analyzers
  • relay test systems

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  • SIQ Ljubljana