Calibration is testing the accuracy of the lab equipment and adjusting it to meet the required standards. After the equipment or instrument has been calibrated, a report and calibration certificate is issued to prove that it has been restored to the manufacturer’s accuracy specifications. Lab equipment calibration is performed by comparing the accuracy of the equipment to the standard of the measuring instrument.
Reasons for Calibrating an Equipment
All types of equipment degrade with time, drifting and losing stability. Using equipment over a long time and rough handling may cause inaccuracy reading in equipment. Frequent calibration of equipment restores its accuracy standards and ensures that it conforms to the specified calibration data. Calibrated equipment promotes productivity and quality and increases the value of the production process.
How Often Should an Equipment be Calibrated
The frequency of calibrating equipment varies from industry and the criticality of the instrument. Critical equipment is calibrated frequently to ensure a quality process. Other equipment can be calibrated periodically or according to the intensity used in a plant. When equipment loses its calibration, it should be re-calibrated immediately. Most types of equipment have the recommended calibration schedule set by the manufacturer. It is important to follow a schedule for optimum production results and avoid losses due to equipment inaccuracy.
Terms Used in Equipment Calibration
The calibration range of equipment refers to the limits of measuring, transmitting or receiving a quantity. It is expressed by defining the lower range and upper range values. The range usually starts from zero to a given span value. For example, if a pressure gauge measures pressure from 0psif to 500psig, the lower range value is zero while the upper range value is 500psig. The calibration range of such a pressure gauge is 0 to 500psig.
Span is the difference between the upper range value and the lower range of equipment. Span is denoted by:
Span = URV – LRV
URV is the upper range value, and LRV is the lower range value.
For example if the range of a pressure gauge is 0 to 500psig, then span = 500 – 0 = 500psig.
The capability of an instrument is the equipment range. It provides the rating of the equipment.
Ranging of an Equipment
Ranging equipment sets both the lower and upper range values to match the required sensitivity. For example, if you want to range a pressure transmitter to provide a range of 0 to 200 bar and output of 4 -40 mA, then the range of such equipment will be:
Zero and Span Adjustment
Both smart and analog equipment is adjusted using zero and span measurements. The adjustment allows setting equipment to any range specified by the manufacturer’s limits. Analog equipment has an interaction between zero and span adjustment. However, smart equipment has no such interaction between zero and span.
Five Point Calibration
The general rule of thumb states that calibration points should be taken between 0, 25, 50, 75, and 100 percent ranges when calibrating equipment. Since calibration is taken at five points, it is commonly known as five-point calibration. When performing a five-point calibration exercise, perform tests from both ends, i.e., increasing or decreasing order.
When conducting field calibration, equipment is not uninstalled from the process. Calibration is performed while the equipment is still mounted. It provides an ambient condition to calibrate equipment in its true process.
Bench or In-Shop Calibration
Under the bench calibration, the equipment is calibrated with a device that simulates its process rather than its actual process in the field. Equipment is uninstalled and taken to the calibration shop, where the simulation is done on a calibration bench.
These are devices that are used to calibrate specific types of equipment. There are different types of calibrators according to purpose. These are:
- Block Calibrators: Calibrate temperature probes such as thermocouples and fluidized baths.
- Signal Reference: Used to calibrate temperature controllers and panel meters.
- Pneumatic Calibrators: Used to calibrate pressure equipment.
These are the various documents that show the calibration history of the equipment. It contains all the calibration information, including the calibration dates and the calibrating technicians’ names.
When calibrating equipment, it should be traceable to an international standard. Traceability ensures that equipment has been properly adjusted according to national and international standards. Most equipments are traceable to the National Institute of Standards and Technology (NIST).
You should follow the calibration principles to ensure accurate and precise results when calibrating your equipment. The calibration instruments used must be traceable to the national and international standards. Biotechnical Services, Inc. provides premier, accurate and timely calibration of every type of equipment. We use the latest calibrating instruments to achieve the highest precision in our calibration. We are an accredited calibration company and ISO certified. Contact us today for your lab equipment calibration.