Measurement and identification of indoor equipment in clean rooms and clean rooms

In pharmaceutical industry enterprises, in accordance with the requirements of GMP standards, it is necessary to enforce the quality certification and legality of production equipment, production systems and production processes. In addition, the production environment of pharmaceutical companies (including air and indoor space) also has an important impact on product quality. Therefore, the sanitary quality of the clean room must also be measured and identified.


Within the framework of the hygienic metrology calibration, it is necessary to determine which measurement points are available and which devices must be metered and tested so that the calibration can be performed regularly. For the clean room in the pharmaceutical production process, the measurement of different detection indicators must be carried out on the equipment in the clean room in accordance with the provisions of Annex C of the ISO 14644-3 standard. In the measurement and measurement, important measuring instruments include: particle counter, aerosol detector, flow detector, differential pressure detector, thermometer and hygrometer. Different sensor systems with suitable detection accuracy will be used for different detection quantities. In addition, in accordance with the requirements of the GMP standard, all testing instruments require periodic calibration. The standard stipulates that the calibration period of various testing instruments is 12 months. The technical feasibility in Annex C of the ISO 14644-3 standard has been converted into a feasibility test for technical implementation in the GMP standard.

Basic information for measurement calibration

The main basic concepts of metrology calibration are:

- metrological calibration: comparing the measured value with the standard value under specified conditions;

- Correction: adjustment to the smallest possible difference;

- Unit of measurement: The unit specified for the testing equipment;

- Compliance: the correspondence between the data obtained during the continuous measurement process and international standards;

- Unreliability of detection: A parameter related to the measurement result and the magnitude of the measurement value identified by the detection control system.

Under normal circumstances, compliance is indicated by a certificate of certification issued by a different level of national certification body. For example, if you obtain the DKD certification, it means that the specified requirements are met within the scope of the DKD standard, because the DKD certification is approved by the international standard certification and approval department. The purpose of metrological calibration is to verify the consistency of the object being tested with the specific criteria. The certificate of conformity certification can only be obtained when the combination of the detection error and the unreliability coefficient of the detection is less than the specified value. In the measurement inspection, according to the requirements of the special technical specifications of the tested object, the ratio of the unreliability of the measurement and the detection error shall be 1:3. That is to say, factors that detect unreliability should be considered when judging the results of the measurement calibration.

Selection of testing instruments

In the Annex C of the ISO 14644-3 standard, the measuring instruments selected for the measurement and calibration according to the ISO 14644-3 standard are given.


When performing room temperature monitoring, a resistance thermometer or a thermistor should be selected as the temperature sensor. The required detection accuracy is 0.5 °C. In today's production site or DKD metrology calibration, the measurement accuracy that can be achieved is 0.1 to 0.2 °C. In Germany, there are more than 30 qualified DKD metrology calibration laboratories.

Relative humidity

According to the requirements of the ISO 14644-3 standard, a humidity sensor with a thin-coated capacitor or a sensor should be used for relative humidity detection. The detection accuracy of such a relative humidity sensor is required to be 2% to 3% of the RH value. Therefore, in the measurement calibration, the unreliability required for detection is about 1%. In Germany, there are few laboratories qualified for relative humidity measurement calibration, but it is sufficient for customers who require relative humidity measurement calibration.

Pressure difference

In order to measure and monitor the pressure difference between the clean rooms, it must be measured within a low differential pressure range (5 to 25 Pa). Starting from 20 Pa, a more accurate pressure balance must be used for metrological calibration. In the low pressure range, in many cases only the difference complement method can be used to estimate the consistency. Only a handful of laboratories can perform metrological calibration of low pressure differentials.

Testo Industrial Services LLC has developed a new low pressure differential pressure measurement calibration method. They use DKD approved wind tunnel equipment. The principle is that the airflow will have a certain pressure drop after passing through the wind tunnel. By adjusting the airflow flowing through the wind tunnel, a stable pressure difference can be obtained at the exit of the wind tunnel while keeping the air flow constant. The pressure difference generated is about 5 Pa at an air flow rate of 3 m/s, and the measurement error is 0.2 Pa; this precision fully satisfies the requirements for metrological calibration of commonly used pressure sensors.

Air flow rate measurement

There are also high requirements for the measurement of the airflow rate. In accordance with the requirements of the ISO 14644-3 standard, hot wire anemometers, ultrasonic anemometers and impeller anemometers suitable for low pressure airflow detection should be used. Frequently done is the metering calibration of an anemometer with an air flow rate in the range of 0.45 m/s. The results of the metrological calibration must prove that the anemometer's error is within ±20%. This requirement is difficult to achieve because the specification of the air anemometer in this case is 0.12 m/s in accordance with the requirements of the ISO 14644-3 standard. In this case, only comparative measurement calibration can be performed to obtain a higher safety factor. At present, the measurement accuracy of three DKD metrology calibration laboratories in Germany has reached 0.1m/s.

Particle content

The calibration of the particle content measuring instrument is more difficult. The allowable error of the particle content detection instrument shall not exceed ±20%. At present, the DKD metrology calibration laboratory is not able to perform calibration work in this area. The metrology calibration of the particle counter can only be performed at the instrument manufacturer. In accordance with the requirements of the ISO 17025 standard, the Federal Competent Authority can provide you with an observation method for the unreliability of the metering and calibration of particle size detectors developed in Switzerland. The unreliability of the metering calibration of the particle content detector is relatively large (about ±10%) when the particle content is low, so it is difficult to prove that the standard specification of ±20% has been met. That is to say: At present, in the measurement calibration of the particle content detector, the traceability of the calibration result is still insufficient.

Summary: In general, the calibration of temperature and relative humidity testing instruments has sufficient inspection accuracy. In the low-speed air flow rate range of 0 to 1 m/s, due to the unreliability of the metering calibration result of the air anemometer, the number of units capable of performing the calibration of such a measuring instrument is too small. The measurement calibration of the differential pressure detector with a pressure difference of 0 to 20 Pa is also similar to the air flow rate detector. For the measurement calibration of the particle content detector, there is currently no calibrated calibration unit authorized by DKD.

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