Multifunction process calibrators are the Swiss Army knives of calibration instruments. They are designed around a sophisticated array of
electronics which, depending upon the range of functions a particular model includes, may be capable of reading and sourcing voltage, current,
frequency and resistance signals from nearly any source. Combining this versatility with the appropriate process connections enables
multifunction process calibrators to calibrate nearly any device that uses those signals as either input or output. Multifunction calibrators
can therefore do the job of pressure calibrators, temperature calibrators, electrical/loop calibrators and more.
Calibration
Process instrumentation, from the simplest to the most complex instruments, requires periodic calibration and maintenance to ensure that it’s
operating correctly. Drift, environmental factors, electrical supply, the addition of components to an output loop, and process changes can all
cause process instruments to lose accuracy. Only by calibrating those instruments can accuracy be assured.
Calibration is a comparison between two devices. The first device is the unit to be calibrated, often called the unit under test. The second device
is the calibrator, which has been fixed to a standard of a known accuracy.
Typically, calibration of an instrument involves checking several points throughout the range of an instrument. Once the accuracy of the device has
been tested, adjustments can be made to bring it to within tolerance.
Calibration Standards
Calibration standards include any source that can provide a known reference point to which the accuracy of an instrument can be compared. Calibration
standards can vary widely. They can include solutions prepared to a specific pH to calibrate pH meters. They also include blocks of a known thickness
from which thickness meters can be calibrated.
Not all standards are created equally. While all standards have a known accuracy, there are some—known as primary standards— that are the highest level
of accuracy for a specific parameter. Primary standards achieve their high accuracy by relying upon measurement technologies using fundamental physical
constants that do not drift. For example, the value of the volt is defined by the Josephson Effect which has an accuracy of 1 part per billion. These
fixed values minimize uncertainty, making primary standards the most accurate calibration tools.
Though the accuracy of calibrators varies pretty widely depending upon the model and the measurement parameters, they can be roughly categorized into
three groups:
- Industrial standards, also known as field standards ideally have, as a rule of thumb, an accuracy 4 times
greater than the instrument being calibrated, though this scale factor varies by industry. These are useful for spot checking sensors at the point
of use rather than a laboratory environment.
- Secondary standards, also known as laboratory standards provide greater accuracy than field standards and
are used to calibrate field standards.
- Primary standards provide the highest calibration accuracy. Primary standards are used to calibrate secondary standards.
Traceability
To improve the quality of a calibration to levels acceptable to outside organizations, it is generally desirable for the calibration and subsequent
measurements to be traceable to internationally recognized standards. Establishing traceability is accomplished by a formal comparison to a standard which
is directly or indirectly related to national standards (such as NIST in the USA), international standards, or certified reference materials.
Using a Multifunction Process Calibrator
The benefit of multifunction process calibrators is their ability to read and source a number of input and output signals such as voltage, current,
frequency and resistance. Since these signals are so common in process applications, this ability allows using multifunction process calibrator to
calibrate most process instruments.
The exact calibration procedure depends on the type of instrument being calibrated. For some instruments such as displays and controllers the calibrator
is used to source or simulate a signal which is read by the unit under test. As the signal sent by the calibrator is of a known accuracy, any discrepancy
is the error of the unit under test. The unit under test can then be adjusted until it displays the correct value.
Sensors and transmitters, on the other hand, can be subjected to test conditions—for example a pressure sensor having pressure applied to it via a hand
pump—and the multifunction calibrator set to read the signal sent under those conditions. Again, the accuracy is easily determined by comparison between
the pressure applied and the signal sent by the sensor.
Often, using a multifunction process calibrator requires little more than the calibrator and test leads. Some applications may require test modules or
other accessories like a hand pump (for calibrating pressure devices).
Some examples of calibration applications involving different signal types:
- Voltage: Voltage signals are extremely common in process applications. They are found in pressure, level, water quality,
humidity, airspeed and many other applications.
- Current: Like voltage, current is a very common signal. It is also integral to current loops found in a wide range of
recorder and datalogger applications.
- Frequency: Frequency signals are often used in applications which utilize pulse output. This includes flow meters and counters.
- Resistance: Resistance signals are commonly found in temperature applications involving RTDs and thermistors.
Things to Consider When Selecting a Multifunction Process Calibrator:
- What type of signal is used by the equipment you wish to calibrate?
- What measurement parameters do the units under test have?
- Where will calibrations take place? The lab? The field?
- What level of accuracy is needed?
- Are any communication protocols needed?
- What types of adapters, if any, are needed to attach the unit under test to the calibrator?
- Is a calibration certificate needed? Which one?
If you have any questions regarding multifunction process calibrators please don't hesitate to speak with one of our engineers by e-mailing us at
sales@instrumart.com or calling 1-800-884-4967.
