The precise acquisition of absolute pressure is of critical importance in many industrial applications. To ensure the accuracy and reliability of absolute pressure sensors throughout their entire service life, regular and traceable calibration is indispensable. In this article, DDM Sensors explains the fundamentals, workflow, and key aspects of professional absolute pressure sensor calibration.
Fundamentals of Absolute Pressure Calibration
Absolute pressure is defined as the pressure relative to a perfect vacuum, the absolute zero point of pressure. Regular calibration of absolute pressure sensors is necessary to detect and correct measurement deviations caused by aging or operating conditions. This not only safeguards process reliability by preventing control errors, but also directly impacts product quality, as precise measurement values enable consistent results that comply with specifications.
Equipment Required for Calibration
- Test Specimen: Central to the process is the absolute pressure sensor to be tested (device under test / DUT), for which the appropriate connection cables and a decontamination declaration must be provided if necessary.
- Reference Standard: A high-precision reference standard (e.g., a deadweight tester or a calibration standard) whose accuracy is significantly higher than that of the DUT.
- Pressure Generation: A stable unit such as a hand pump or a programmable pressure controller is used for pressure generation.
- Data Acquisition: Measurement values are recorded via systems such as multimeters or data loggers.
- Ambient Measurement Technology: In addition, specialized ambient measurement technology is required to monitor temperature and atmospheric humidity.
- DDM Special Service: Calibration across widely varying temperatures from -40 to +150 °C.
- Test Line: An assortment of connection elements and seals for setting up a leak-tight test line is also essential.
The Calibration Process for Absolute Pressure Sensors at DDM Sensors
Step 1: Preparation of the Measurement Setup
Preparation begins by safely isolating the sensor from the process and completely depressurizing it. Next, we perform a visual incoming inspection to check the test specimen for external damage. A critical step is allowing the sensor sufficient time to adapt to the stable conditions in the laboratory (acclimatization) to minimize thermal influences on the measurement result. Finally, the sensor is carefully integrated into the test line without leaks to ensure a tight and stable measurement setup.
Step 2: Execution of the Measurement Series
After installation in the calibrator, the sensor is first subjected to preloading to stabilize mechanical settling effects. Subsequently, we target defined calibration points across the measuring range, for example at 0%, 25%, 50%, 75%, and 100%. At each point, the measurement values of the reference standard and the test specimen are precisely recorded. To evaluate the sensor’s hysteresis, the measurement is carried out as both an increasing and a decreasing series, while strictly maintaining the necessary stabilization times at each measurement point. Upon request, we perform this pressure calibration at specific temperatures within a range of -40 °C to +150 °C.
Step 3: Evaluation and Adjustment
Following the measurement series, we calculate the deviation between the values indicated by the test specimen and the true values of the reference standard for each calibration point. We compare these deviations with the manufacturer’s specifications or the tolerances defined in standards to assess compliance and make determinations regarding linearity and hysteresis. Should the deviations lie outside the permissible limits, we perform a zero and span adjustment on adjustable sensors. To validate the success of the adjustment, the measurement is then repeated and documented as an “As-left” calibration in the final calibration certificate.
Key Influencing Factors and Best Practices
A high-quality calibration depends on the meticulous control of several influencing factors. Stable environmental conditions regarding temperature, atmospheric pressure, and humidity in the laboratory are fundamental to achieving reproducible results. The accuracy of the reference standard used is also critical; here, a sufficient test uncertainty ratio (TUR/TAR) between the standard and the test specimen must be ensured. Other important factors include the stability of the pressure generation, the correct and stress-free mounting of the test specimen, and the seamless documentation of “As-found” (condition upon delivery) and “As-left” data (condition after adjustment) to track the history of the measuring equipment.
Calibration Certificates and Compliance with Standards
A calibration certificate is the official document that records the results and boundary conditions of a calibration and proves metrological traceability to national standards. A distinction is made between a factory calibration, which certifies compliance with internal quality standards often based on ISO 9001, and an accredited calibration (e.g., according to DAkkS / ISO 17025), which takes place under the stricter requirements of a national accreditation body. Such certificates are of great importance particularly for audits within the framework of quality management systems like ISO 9001, as they provide proof of inspected and compliant measuring equipment.
Professional Calibration from DDM Sensors
DDM Sensors offers professional calibration for both working sensors and reference standards. Our service includes factory calibrations according to ISO 9001 as well as, in cooperation with our partners, accredited DAkkS calibrations according to ISO 17025. Through the use of high-end equipment, we ensure minimal measurement uncertainties and guarantee the highest precision.
Get Expert Advice on Absolute Pressure Sensor Calibration Now
Request a professional calibration for your absolute pressure sensors from DDM Sensors now or schedule a non-binding consultation with our experts.
Frequently Asked Questions About Absolute Pressure Sensor Calibration
How often do absolute pressure sensors need to be calibrated?
Absolute pressure sensors do not have a fixed standard interval; how often calibration is required depends on several factors:
- Criticality of the measurement: The greater the impact on safety, product quality, or regulations, the more frequent the calibration.
- Required accuracy: Tight tolerances demand shorter intervals.
- Operating conditions: Temperature changes, pressure pulsations, overpressure, vibration, and corrosive media accelerate drift.
- Sensor stability: The manufacturer’s long-term drift specification is the central reference point.
- Industry requirements: Criteria from ISO 9001 or industry-specific regulations. As a general guideline, an initial interval of 12 months is usually chosen, which is then extended or shortened based on the calibration history (As-found values). Additionally, event-driven recalibration should be carried out, e.g., after overpressure, a drop, or repairs.
What does As-found/As-left mean?
As-found and As-left describe the state of a sensor before and after calibration:
- As-found: The measurement values prior to calibration, i.e., before any modifications are made. They show how far the sensor has drifted since its last calibration and form the basis for evaluating the calibration interval.
- As-left: The measurement values upon completion of the calibration. If the sensor was adjusted, they document the corrected state; if no adjustment was necessary, they correspond to the As-found values.