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About Multifunction Calibrators

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Multifunction Calibrators can be nicknamed the "do everything instrument" and are typically portable and can measure and source multiple DC signals such as voltage, current, frequency, pulse, resistance and power. They can be fitted with special probes to give them the capability to measure AC current and voltage. They also have the capability to measure pressure and unique to GE Druck DPI620 Genii they also add the capability to generate pressure as well.

Some examples of their capabilities are:

  • VOLTAGE: Very common in process applications, used in petrochem, water, level, humidity, aerospace (airspeed) and many other applications.
  • CURRENT: The most common process signal, and integral to 4-20 mA current loops used in most industrial automation applications.
  • FREQUENCY: Used in a variety of process applications such as counters and flow meters.
  • RESISTANCE: Commonly used in temperature applications such as aResistance Temperature Detector (RTD) and thermistor.
  • DIGITAL SIGNALS: HART and Field Bus Communications are the most common process digital signals used with sensors and instrumentation.

The HART Communications Protocol (Highway Addressable Remote Transducer Protocol) ia a digital industrial automation protocol which communicate over legacy 4-20 mA analog instrumentation wiring.

Fieldbus is the name of a family of industrial computer network protocols used for real-time distributed control, standardized as IEC 61158. SENSORS and PROCESS TRANSMITTERS: A multifunction calibrator can simultaneously power up and measure a variety of sensor types. For example, a pressure transmitter can be powered up and have its signal output measured against a pressure reference built into the multifunction calibrator.

Once the device under test has been tested, it can be adjusted to bring it into tolerance. This is called, calibration!

Benefit of Multifunction Calibrators

The main advantage of using multifunction process calibrators is simple: they are able to read and source many different common process signals such as current, voltage, frequecy, frequency, pulse, and resistance. By using just one instrument, it is possible to measure and calibrate most sensors, transmitters and instruments used in process applications.

Process instrumentation and sensors require periodic calibration and maintenance, and change over time and/or usage due to drift, environmental factors, process changes, output loop changes and what not. It is important that the information we get from measurements is “reliable and accurate”.

Multifunction calibrators are designed to source and measure electrical signals such as voltage, current, resistance, and frequency, and pulses so as to verify the accuracy of sensors and measuring instruments. With options they can also measure/source pressure.

Why Calibrate?

Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device. The device with the known or assigned correctness is called the standard. The second device is the unit under test, test instrument, or any of several other names for the device being calibrated.

The calibration procedure depends on the type of sensor or instrument that is to be calibrated. The calibrator generally sources or simulates a signal with known accuracy which is read by the unit under test (UUT). Any discrepancy is the error of the UUT, and can then be adjusted until it displays the correct value. Typically, the UUT is checked at several points throughout its calibration range.

Through a calibration process, knowledge is transferred from one device to another. “A good rule of thumb is to ensure an accuracy ratio of 4:1 when performing calibrations. With today’s technology, an accuracy ratio is becoming more difficult to achieve.”

Traceability

To communicate the quality of a calibration the calibration value is often accompanied by a traceable uncertainty statement to a stated confidence level. This is evaluated through careful uncertainty analysis.

In many countries a National Metrology Institute (NMI) will exist which will maintain primary standards of measurement (the main SI units plus a number of derived units) which will be used to provide traceability to customer's instruments by calibration. The NMI supports the metrological infrastructure in that country (and often others) by establishing an unbroken chain, from the top level of standards to an instrument used for measurement. Examples of National Metrology Institutes are NPL in the UK, NIST in the United States, PTB in Germany and many others. Since the Mutual Recognition Agreement was signed it is now straightforward to take traceability from any participating NMI and it is no longer necessary for a company to obtain traceability for measurements from the NMI of the country in which it is situated.

Questions to ask yourself when deciding on which Electrical Calibrator to Choose:

  • What type of signals are used by my equipment?
  • What measurements are critical to my process and that need to be calibrated?
  • Where will I calibrate? In the field or in the lab?
  • What accuracy / precision is required?
  • Are any communication protocols needed (HART, Field Bus etc)?
  • What type of calibration certification is needed: As Left / As Found and As Left Data, NAVLAP Certification etc?
  • What about adaptors (if any are needed) to connect your multifunction calibrator to your UUT (UUT = Unit Under Test, which could be a sensor, transmitter or instrument)?

If you have any questions regarding electrical calibrators please call to speak with one of our engineers