What is calibration and how can IIoT help manage reports?

Calibration can be simply described as the process of comparing the measured value from an instrument under calibration with a reference standard of known and high accuracy. In essence, it establishes whether the instrument provides measurements within acceptable limits.

Performing calibration requires specific tools and instruments, which vary depending on the type of calibration. Common examples include calibrators with valid calibration certificates, standard devices, and calibration rigs.

Calibration is essential to ensure accurate measurement. Measuring devices are installed in diverse industrial environments where they are exposed to challenges such as abrasion, vibration, sudden temperature changes, harsh conditions, and mechanical shocks. These factors can affect device performance, making calibration necessary to verify accuracy and, if required, adjust the instrument to meet application specifications.

Accurate calibration positively impacts production processes by ensuring reliable measurements. It also reduces variation within technical specifications, supports preventive maintenance, and guarantees measurement traceability.

Additionally, modern smart instruments - such as those equipped with Heartbeat Technology from Endress+Hauser - provide continuous health status information, offering a clearer picture of device condition and measurement reliability.

During calibration, all measurements must be recorded, either manually or through an automated system. Upon completion, a final document - known as the calibration certificate - is generated, containing all technical details of the procedure.

Typically, the certificate includes comparisons between the calibrated device and the traceable reference standard. It must also provide technical specifications of both instruments, procedural data, calibration uncertainty, calibration number, and the signatures of authorized personnel.

All measuring devices can be calibrated to ensure proper functionality and the level of accuracy required for their application. While the concept of calibration remains consistent, the procedure varies depending on the type of field instrument.

For example, calibrating a pressure transmitter may involve using a calibrated deadweight tester as a reference to generate pressure. Alternatively, another pressure device with higher accuracy than the instrument under calibration can be used.

All calibration standards must include a valid calibration certificate confirming compliance with applicable standards in the relevant region.

Calibration involves comparing the device under test with a reference standard, typically at multiple points across the measuring range—commonly 0%, 25%, 50%, 75%, and 100%. Additional test points can be included if required, although this may increase costs.

The reference standard used depends on the type of device:

• Flow transmitters: Calibration may involve a master device, comparison with a weight scale, or mobile prover calibration.
• Pressure transmitters: A higher-accuracy standard device, digital calibrator, or deadweight tester is typically used.
• Temperature transmitters: A calibrated reference such as an electronic temperature sensor simulator is applied.

Calibration procedures are guided by a Standard Operating Procedure (SOP) that outlines each step. The interval between calibrations is not universally defined but can be determined based on factors such as:

• Device type and application
• Manufacturer recommendations
• Trend analysis from previous calibrations
• Instrument historical data
• Comparison with similar devices in the plant
• Required measurement accuracy

Calibration is generally understood as the process of comparing a device with a reference standard of higher and known accuracy. Adjustment, if required, follows calibration to correct deviations identified during the comparison.

During calibration, the procedure involves verifying the measuring range against the reference standard. If an error greater than the acceptable limit is detected, the instrument must be adjusted.

For example, adjusting a pressure transmitter typically involves trimming the zero and then the span value. These parameters can be modified through mechanical or software settings, depending on the device’s age and manufacturer specifications. After adjustment, the measuring range must be rechecked against the standard to confirm that accuracy meets the required limits.

On-site calibration is a common practice in industrial environments, particularly during planned production shutdowns when multiple instruments require calibration. In such cases, external service providers are often engaged to calibrate pressure, temperature, and flow instruments.

Field calibration, including flow calibration, is increasingly prevalent. Many companies now employ mobile calibration rigs to perform these services directly on-site. For example, Endress+Hauser offers on-site calibration using advanced mobile rigs and certified professionals.

The benefits of on-site calibration include eliminating the need for instrument transportation, enabling immediate adjustments and repairs, and facilitating quick instrument replacement - all performed by qualified experts. This approach reduces downtime and ensures compliance with calibration standards.

The frequency of calibration depends on several factors, as there is no universal standard. Best practices suggest considering the following points when defining calibration intervals:

• Criticality of the measurement to the process
• Quality system requirements at the plant
• Regulatory compliance
• Manufacturer recommendations
• Impact of failure due to lack of accuracy
• Other technical requirements

These factors help establish an appropriate calibration schedule, which can be adjusted as needed. Modern IIoT solutions further simplify calibration planning and execution by providing easy access to device data and scheduling tools.

Calibration uncertainty refers to the degree of doubt associated with the calibration process and is influenced by factors such as installation conditions, reference traceability, and environmental variables. If calibration uncertainty exceeds the tolerance of the instrument being calibrated, the validity of the calibration must be questioned.

For example, using a clamp-on flow meter to calibrate an in-line device may result in calibration uncertainty higher than the installed meter’s tolerance, making the process ineffective.

A device under test can either pass or fail calibration based on its tolerance limits, which are defined by the manufacturer or specified in the initial calibration certificate. During calibration, if the measured error exceeds the tolerance limit, the calibration is considered failed. In such cases, the device should be adjusted and recalibrated. If the difference between the calibrated device and the reference standard falls within the tolerance limit after adjustment, the device passes.

Proper storage and accessibility of calibration documents are essential. Modern IIoT services, such as Netilion Library, enable centralized cloud-based management of calibration reports, technical data, and related documentation under each device tag. This approach ensures that all team members can access, share, and update information efficiently, saving time during field verification or when retrieving historical calibration records.

When integrated with edge devices, IIoT platforms can automatically create digital twins of all instruments, making files accessible from smartphones, tablets, and laptops. This simplifies collaboration and ensures that technical documentation and calibration reports are always available, improving efficiency and compliance.