At present, China has not yet issued verification procedures or calibration specifications for the measurement parameters of high-pressure steam sterilizers and other related sterilization equipment. The experimental personnel lack the necessary technical basis in the process of regular calibration. This paper discusses the calibration methods for pressure, temperature, time and other parameters of high pressure steam sterilizer, and provides a variety of calibration methods for experimental rafts for safety supervision.

First, the basic parameters of the high pressure steam sterilizer

Basic parameters:

1 rated working pressure is not more than 0.25MPa.

2 sterilization working temperature: 115~138 °C.

Pressure indicator calibration method:

To ensure the reliability of field calibration results, the following basic principles should be followed:

1) Environmental conditions:

Temperature: (20 ± 5) ° C; if not guaranteed, can be appropriately relaxed. However, the temperature effect needs to be assessed and corrected in the calibration results.

Relative humidity: no more than 80%.

2) Measurement standard:

The measuring range of the selected standard device shall be greater than or equal to the measuring range of the pressure indicating instrument. The absolute value of the maximum allowable error of the indicated value shall not be greater than 1/3 (digital) of the absolute value of the maximum allowable error of the instrument. 1/4 (analog).

Second, high pressure steam sterilizer pressure calibration method

1 , method one field calibration method

This method is suitable for high pressure steam sterilizers with small working volume and manual discharge valves, such as portable and vertical. Usually, the high-pressure steam sterilizer is equipped with a metal hose at the end of the vent valve to facilitate the proper discharge of cold air. Therefore, it is only necessary to connect the metal hose with the pressure checker for verification to ensure airtightness, that is, to perform on-site calibration of the pressure indicating instrument of the high pressure steam sterilizer according to the verification procedure.

Operation points:

The pressure resistance of the metal hose needs to be greater than or equal to 400 kPa. If it cannot be reached, it must be replaced with a pressure connection hose that meets the requirements. The pressure tightness of the calibration system should not exceed 0.1 kPa/min.

Calibration equipment:

The standard device uses a digital pressure gauge (not less than 0.2, the upper limit does not exceed 500 kPa) or a precision pressure gauge (not less than 0.4, the upper limit depends on the pressure indicating instrument to be inspected), and the accessory equipment is selected for gas pressure verification. (Stability is better than 0.02% FS, working pressure is greater than 600 kPa).

The upper limit of the pressure calibration of the field calibration method is often limited by the rated working pressure of the safety valve installed on the autoclave. When the upper limit pressure of the pressure indicating instrument is not calibrated, the calibration value of the highest rated working pressure can be given.

2 , method two direct comparison method

This method is suitable for autoclaves equipped with test connectors. Usually large, direct steam.

Operation points:

Connect the pressure standard to the pressure connector in the sterilizing chamber line. If the pipe thread on the pressure connector does not match the pressure standard thread, a transfer method should be adopted to ensure reliable connection and air tightness requirements.

Calibration equipment:

The standard is recommended to use a digital pressure gauge (not less than 0.2, the upper limit does not exceed 500 kPa), its use environment should be able to reach 140 ° C, and the metering performance is constant or can be corrected. If a spring tube type precision pressure gauge (not less than 0.4, the upper limit value depends on the instrument to be inspected), the allowable error should take into account the additional error caused by the temperature change.

Its indication error ΔPn is calculated as follows:

ΔPn ≤ ±(δ + 0.04Δt)% ×Pm (1)

In the formula:

Δ-accuracy level,

Δt - the difference between the temperature used and the temperature at the time of calibration,

Pm-range.

All calibration items are only for pressure indication errors.

The direct comparison method uses the steam pressure in the sterilizer as the working medium. Due to the limitation of the working pressure of the steam, the calibration point cannot cover the range of the pressure indicating instrument according to the regulations, and can only rely on the pressure controller or the temperature controller. The pressure calibration point is determined within the pressure or temperature range of the fungus. Because the sterilizer requires constant pressure at the selected working pressure, but it can't be done, there is always pressure fluctuation, so the calibration must be fast and accurate, and the method of averaging multiple readings is used. Determine the calibration result.

Calibration result processing:

Pressure indication error

ΔP = Pa-Pn (2)

In the formula:

ΔP-calibrated pressure indicator indicates value error, kPa;

Pa-received pressure indicator indicates the average value of the reading, kPa;

Pn-standard display reading average, kPa.

3 , method three real-time comparison method

This method is suitable for all types of autoclaves, and the standard is connected by wireless measurement.

Operation points:

The standard device is set according to the requirements of the instruction manual. After completion, it is placed directly in the sterilization room near the pressure indication instrument to be inspected, and the sterilizer is activated to perform calibration work when the normal working state is reached. During the calibration process, attention should also be paid to the effect of pressure fluctuations in the autoclave on the calibration results.

Calibration equipment:

Pressure wireless measurement system (accuracy is not less than 0.2, the upper limit of measurement is not more than 500 kPa, the use environment is not lower than 140 °C), the pressure can be measured in real time and the measurement results can be displayed and recorded.

The real-time comparison method also uses the vapor pressure in the sterilizer as the working medium, so the calibration method is the same as the direct comparison method. The standard device indication value is generally collected and recorded by the computer at intervals. Only the indication value of the instrument to be inspected is recorded during the calibration. Compared with the direct comparison method, the installation position is flexible, the operation method is simple, the applicability is stronger, and the microcomputer is used as the display recording device in the calibration process, so the calibration process is intuitive and controllable, and the customer is more acceptable. The calibration result is processed according to formula (2).

4 , method four record comparison method

This method is also applicable to all types of autoclaves, and the operating points are the same as in real time comparison. The standard device uses a recorded pressure wireless measurement system, and its technical specifications are unchanged. Compared with the standard device used in the real-time comparison method, the volume is smaller and suitable for a smaller working space. However, the recording type lacks the real-time measurement data transmission function, and the calibration process cannot be accurately grasped, and the recording result can only be passively accepted. In order to make the measurement results reliable, it is often necessary to extend the calibration time, or when the calibration result is not satisfactory, it is often necessary to perform multiple operations to obtain the best calibration result. The calibration result processing is also in accordance with equation (2).

Third, high pressure steam sterilizer temperature calibration method

Place the temperature sensor at the center of the autoclave and let the autoclave perform a complete sterilization process. During the heating process, carefully discharge the air from the sterilizer chamber. After reaching the sterilization temperature, test a set of data every 2 minutes, test for 30min, get 15 sets of data, the temperature fluctuation is the actual temperature maximum in the measured 15 sets of data minus the actual temperature minimum, divided by 2, and crown Expressed as "±". GB/T30690-2014 proposes that in the sterilization cycle, the measured value of the sterilization temperature range is generally not higher than the set value of 3 ° C, and the pressure range should correspond to the measured temperature range. At the same time, the measurement uncertainty should be less than one-fifth to one-third of the maximum allowable indication error of the device under test, that is, 0.6-1.0 °C. This article focuses on the central point temperature and pressure calibration results of autoclaves of different volumes under two common calibration methods. The calibration ambient temperature is 20.0 to 21.0 ° C and the ambient relative humidity is 45% to 50%.

There are two common calibration methods for temperature:

Method 1: Wireless temperature and pressure data collector calibration method

The wireless temperature and pressure data collector records the temperature and pressure data collected by the sensor in the collector. Before the test, the wireless temperature and pressure data collector sets a corresponding program, and the collector is placed at the center of the sterilizer cavity to be calibrated. After the test is finished, the recorded data is read by the signal converter and software provided by the computer. At present, the temperature test accuracy of this type of data collector is ±0.1 °C, the pressure test accuracy is ±0.1KPa, and nearly 20,000 data can be recorded at a time. The working power is lithium battery in the device, and the service life is about 5 years. . This calibration method is because the external connection line is not introduced, the sterilizer cavity is sealed well, and the data is true and reliable. The device can directly measure the actual pressure value in the sterilizer cavity, but the initial cost of the device is up to the number. 100,000 yuan, and the service life is only about five years, you need to read and analyze the data collected by computer. If you need to monitor the data in real time, you need to invest higher funds. Therefore, such devices have not been widely popularized in the group of calibration and calibration mechanisms, sterilizer users and the like.

Method 2: Thermocouple calibration

Thermocouple is a common temperature sensor. Before testing, put a thin T-type thermocouple (generally ≤1.0mm) at one end of the high-pressure steam sterilizer cavity, cover the high-pressure steam sterilizer, and Try to make it sealed. After the autoclave starts working, a small amount of steam will overflow through the thermocouple outlet, but the autoclave can continue to heat up. During the heating process, the air in the sterilizer chamber is completely discharged. When the autoclave is in a sterilized state, the temperature data is collected by a data collector. The measured temperature data is converted to the theoretical pressure value according to the Antoine equation and compared with the data measured by the wireless temperature and pressure data collector. The method uses the thermocouple which is widely used at present, which makes the calibration of the high pressure steam sterilizer convenient and simple, but due to the introduction of the thermocouple, there is always a leak point in the whole sterilization process, to a certain extent, The test results have an impact.

Fourth, summary

Compared with the four pressure calibration methods, the real-time comparison method has outstanding advantages, not only the operation is simple, but also the calibration process is visible. The pressure fluctuation in the pot can be reduced by the method of synchronous reading, the calibration result is reliable, and the uncertainty is small. When a thermocouple is used to calibrate an autoclave, there is a small leak, and there is a certain deviation in temperature calibration. Whether using a wireless temperature and pressure data collector or a thermocouple to calibrate the autoclave, the heating process is in accordance with the Clausius-Clapeyron equation.