Views: 3 Author: Site Editor Publish Time: 2021-05-18 Origin: Site
First, the principle of photometric method
At the upstream end of the filter to be tested, the PAO aerosol is used as a dust source, and the mixing uniform to be gas-free is also stabilized, and the concentration value is set to a reference value when the upper concentration value is stabilized. After the upstream concentration value is set, do not adjust the PAO aerosol concentration. Use the photometric to scan downstream of the filter, detect the ratio of aerosol concentration, downstream concentration and set upstream concentration, is the leakage of the filter (also known as transmittance).
Second, test conditions
To test the leak rate of the filter, you must meet three conditions:
1. Introduce the aerosol into the system.
The introduction of aerosol is a negative pressure end of the fan. At this time, the dust particles generated by the generator can be inhaled by the fan, the aerosol is small to the environment; the aerosol is mixed is relatively uniform; dust elimination does not need to be positive and closed, and the dust is difficult. For example, the FFU is ventilated, the clean workbench is venting.
Some things that do not have conditions can only be dusty in the position close to the filter. At this time, it is necessary to overcome the airflow pressure on the upper end of the filter to press the aerosol into the stasis, and the dust is difficult; if the dust is leaked to the field test The environmental aerosol is more, the gas sol concentration is high, easy to interfere with the test; the aerosol mix is uneven, and the upstream concentration fluctuates greatly. We don't recommend it here unless it is no longer.
Some equipment manufacturers do not have related test experience, set the aerosol dust port in the positive pressure of the fan, bringing a lot of unnecessary trouble to the test. So everyone must write this point in writing, requiring equipment manufacturers to set the dust port in the negative pressure of the fan, and create favorable conditions for later verification.
2, can detect the upper ride concentration of aerosols in a stable uniform.
The upstream concentration test port is provided in the place near the upstream end of the filter, and the hose is connected to the position of easy sample, such as purifying the air-conditioning system room to send air-fit static pressure box. Some old static pressure boxes do not have upstream concentration test ports, the static pressure box must be transformed.
3, can be scanned by point-by-point scanning of the filter downstream end of the filter.
If you can scan your point-by-point, you can measure the leakage of the filter including the border, and a small amount of production equipment is not possible to scan the point-by-point, at which point the overall leakage rate of the filter out of the device. .
Third, test steps (take the purification air conditioner unit as an example)
1, determine the upstream concentration sampling port
2, determine the dust position
Since the air conditioner group is far from the filter, the aerosol can be thoroughly mixed in the air conditioner unit, and the concentration of aerosol concentration in each filter is very stable, which is generally selected in the air conditioner. In order to avoid the neutral filter blocking a large amount of aerosol particles, the dust-free specific location is selected at the rear end of the neutral filter. Although it is not in the negative pressure of the fan, the aerosol generator can be placed in the air conditioner in the air conditioner, so dust collecting is not difficult.
The rear end of the mid-range filter can be placed directly in the rear end of the aerosol generator; if there is no maintenance door in the back of the medium-effect filter, it can be removed, and the aerosol occurs. Place the rear end of the neutral filter.
3, dust, test upstream concentration
The aerosol generator is energized to increase the temperature to 400 ° C or higher. Using an inert gas source to connect the aerosol generator, the gas pressure is adjusted to make the aerosol generator dust.
The aerosol concentration was tested at the upstream concentration test. When the upstream concentration was stable, this concentration was set to the reference concentration. The change in the upstream concentration should not exceed ± 15% of the average measurement value, and the concentration should be 20-80 mg / m3.
For the upper reaches, we understand that after the upstream concentration is set, check the upstream concentration of immediate fluctuations, if the fluctuation value is between 85% -115% set, that is, the upstream concentration is stable, carry out testing.
4, scan test
Scanning the entire filter of the entire filter with the sample header of the photometer, including the filter medium, filter border, filter border and the static pressure box, the static pressure box itself). When scanning, the sampling head is less than 5 cm from 5 cm, and the speed is less than 5 cm / s. Scanning should go back to the compound, and the lines should overlap.
5, qualified standard
ISO14611-3 specifies: The photometric leakage confirms that the standard transmittance of the local leakage of the filter is 0.01%, that is, when the sample probe is aligned with the filter out of the wind surface, still detection, if the transmittance is measured It is considered to be a drain point above 0.01%.
If the filter is 99.99%, then the specified transmittance is not higher than 0.01% is reasonable. If the filter is 99.995%, why allow the transmittance not 0.005% but 0.01%? Forced a qualified value of 0.01%, the filter is too harsh than the filter with less than 99.99%, and the filter is too relaxed for a filter with a higher efficiency than 99.99%.
British Standard BS EN 1822-1 \"HIGH EffICIENCY AIR FILTERS (HEPA AND ULPA) Part 1: Classification, Performance Testing, Marking is reasonable. It is well known that 1 minus the efficiency of the filter is the large transmittance allowed by the filter. This standard specifies that the local transmittance of the filter does not exceed 5 times that allows the large transmittance, and the overall average transmittance does not exceed the allowable large transmittance to determine the filter qualified. For example, the efficiency of 99.995% of the filter should be 0.005%, then as long as its local transmittance does not exceed 0.025%, the overall transmittance is not more than 0.005%, that is, it can be judged.
Therefore, for a filter having a efficiency of 99.99%, we use 0.01% as a standard that determines if it is qualified. For filters that are not 99.99% efficiency, we will negotiate with our customers to develop a more reasonable qualification standard.
6, filter repair, replacement and reconfusion
If the leak rate of any part is found, the leak point can be repaired with glass glue. The plug area of a single leak point cannot exceed 1% of the total area of the filter, and all plug-in area cannot exceed 5% of the total filter. If the plug is still unable to fix the filter, the filter must be replaced. After any form of plugging and replacing the filter, the filter must be re-detected until all standard requirements are met.
Fourth, the test cycle
\"Drug GMP Guide\" for the test cycle: Filter leak test is generally once a year, but the aseptic production area is generally required to test every 6 months.