Electrical Calibration

What is electrical calibration?

 
Electrical calibration refers to the process of verifying the performance of, or adjusting, any instrument that measures or tests electrical parameters. This discipline is usually referred to as dc and low frequency electrical metrology.  Principal parameters include voltage, current, resistance, inductance, capacitance, time and frequency.  Other parameters, including electrical power and phase, are also in this segment of metrology.  Ratio metric comparisons of similar parameters are often performed to compare a known parameter to an unknown similar parameter.

Electrical calibration involves the use of precise devices that evaluate the performance of key properties for other devices called units under test (UUTs).  Because these precise devices have thoroughly known performance characteristics compared to the UUT, performance evaluation and/or calibration adjustment of the UUT to identify or minimize errors is possible.  Typically, the performance of such precision devices should be four or more times better than the UUT. 

These precision devices fall into two broad categories. Electrical signal sources are often referred to as either calibrators or standards. Precision measurement devices are often classified as precision digital multimeters, measurement standards, or ratio bridges.
 
Calibrators and standards
A calibrator is usually able to provide a wide range of precision output signals, such as voltage settings ranging from as little as a few microvolts, increasing through several decades of millivolts, and volts, up to a common maximum of about one kilovolt. 

Additionally, modern calibrators commonly provide outputs for various different electrical functions (such as voltage, resistance, and current).

5522A Multi-Product Calibrator »
A standard is considered to be even more precise than a calibrator.  It is capable of performance that is about four or more times better than a calibrator.  But this improved performance is usually limited compared to a calibrator.  Often a standard can provide only one electrical function, and with only a single output setting, or a few output settings.
734A Reference & Transfer Standards »
Precision digital multimeters, measurement standards, and ratio bridges
Precision digital multimeters (dmms) provide excellent measurement performance of various electrical parameters, through a number of decades of values.  Measurement functions usually include voltage, current, and resistance.  Less commonly, frequency, capacitance, and others can also be included.  The higher performance category of a measurement device is termed a measurement standard, or possibly even a measurement bridge.  These devices commonly have fewer functions but better performance than precision dmms.

8508A Reference Multimeter »


752A Reference Divider »
 
For proper calibration, there are additional needs beyond only using precision devices to evaluate the UUT.  These precision devices must themselves be routinely calibrated in a manner which agrees with (or is traceable to) an international standard of the parameter being evaluated.  This is evidenced through an unbroken chain of documented comparisons with increasingly better standards.  Eventually this chain of compared standards includes a recognized national, international, or intrinsic standard.

 



Fluke uses a J-Array for corporate traceability in its primary standards lab »
 

Related reference materials

Why Calibrate? Video »

Why Calibrate? Application Note »

 
The workload for dc and low frequency ac electrical metrology can include a wide variety of test and measurement instruments:  digital multimeters – analog or digital,  bench or handheld  – oscilloscopes, ScopeMeter® Test Tools, power and energy meters, RTD and thermocouple thermometers, process instrumentation, data loggers, strip and chart recorders, and more. The functions of the calibrator must meet all, or essentially all, of the test equipment functions being calibrated.  Most importantly, the calibrator must have better performance than the required test specifications of the workload.

The normal rule of thumb is that a calibrator or standard must be four or more times better than the specification being evaluated for performance, or the specification referenced for an adjustment process.

Successful selection of a calibrator involves a thorough analysis of the specifications of both the equipment to be tested and the calibrating standards.  This analysis is usually based on the manufacturer’s recommended specifications for the tested equipment versus the standard specifications of the calibrating instrumentation.

The term compliance describes the amount of electrical drive a calibrating source can provide to the electrical load created by the measuring instrument being tested.  A calibrator has a specifically limited drive while not compromising the accuracy of its signal.  Certain test instruments (for example, certain analog meters and panel meters) are relatively large loads and require significant electrical drive from the calibrator.  Therefore, compliance is an important consideration within specification performance.

Measurement  and sourcing
Calibration involves both types of applications where precision measurement and precision sourcing are required.  A precision source is used to test a measurement instrument, and a precision measurement device tests a sourcing instrument.  It is considered a requirement of good metrology to have a quality assurance program that incorporates a routine check of the lab’s calibrating instrumentation.  Because of this, a lab should be equipped with precision measurement instruments with similar performance specifications to the lab’s precision sourcing instruments (both by functionality and spec).  Routine inter comparison will then insure confidence in the consistency of the lab’s instruments and will detect problems early so proper corrective actions can be taken.  Hence, it is considered best practice to have and use both categories of instrumentation in a calibration facility.

 

Related reference materials

Electrical and RF calibrator Selection Guide

A Guide to Oscilloscope Calibration Using Dedicated or Multiproduct Calibrators

Understanding And Comparing Instrument Specifications

Understanding Specifications for Precision Multimeters

Fluke Calibration Certificates

 

Fluke Calibration makes a full line of multi-product, multifunction, and other electrical calibrators along with electrical standards that are used in primary electrical laboratories around the world. Access any of them using the Quick Links at right—or find descriptions of each product group below.
Quick Links
Electrical Calibrators »
Electrical Standards »
Bench Multimeters »
Electrical Cal Software »
  • Electrical Calibrators »

    An electrical calibrator, or dc calibrator from Fluke Calibration includes many innovative and multi-functional solutions to help laboratories operate efficiently, increase throughput, and comply with today’s quality standards. Versatile models and options provide a wide range of possibilities to match a variety of workloads and budgets. Electrical calibrators include: Multi-product calibrators; multifunction calibrators; oscilloscope calibrators; power calibrators; pressure/temperature calibrators.
    Electrical Calibrators
  • Electrical Standards »

    To verify the performance of an electrical calibrator or dc calibrator, you need an electrical standard. Fluke Calibration standards are found in primary calibration laboratories across the world. A wide range of electrical standards and frequency standards are designed to meet the needs of today’s laboratories for traceability and quality accreditation while also being portable, simple to use, and easy to support. Electrical standards include: Voltage standards; ac/dc transfer standards; ac measurement standards; resistance standards; ratio standards; current shunts.
    Electrical Standards
  • Bench Multimeters »

    Fluke Calibration meters have the precision and versatility to handle the most demanding measurements, on the bench or in a system. These instruments are easy to use and offer excellent value that makes them an ideal solution for many applications. Standards laboratory meters include: Reference multimeters; precision digital multimeters; bench multimeters
    Bench Multimeters
 
Fluke Calibration's electrical calibration products are sold in the Europe/Middle-East and Africa through a network of distributors.

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