How to agree on the allowable deviation for FFU acceptance? Measuring points, working conditions and retest rules
Why can't the allowable deviation just be written as a number?
In FFU acceptance, a common requirement is that the wind speed reaches a certain target value. For example, the average wind speed on the wind outlet reaches 0.45 meters per second. However, if only one target value is written during acceptance and there is no agreement on the allowable deviation, it will be difficult to determine whether the on-site measurement results are qualified or not.
There are fluctuations in the measurement itself. The same FFU is measured at different times, at different locations, and with different instruments, and the results may be slightly different. If there is no agreement on the allowable deviation, it is easy for both parties to have inconsistent understanding of the results. If only the average deviation is agreed upon but not the local deviation, it may happen that the average value is acceptable but the local wind speed is low.
Therefore, the allowable deviation should be agreed together with the measurement points, working conditions and retest rules, rather than an isolated number. Aili Industry has complete production capabilities in FFU complete machine testing and acceptance cooperation, and can explain the measurement conditions and judgment calibers. For the basic structure of the FFU machine, you can refer toAili Industrial FFU fan filter unit。
How to agree on measuring points and measuring methods
The location and number of measuring points are the prerequisite for allowable deviation. Measuring points should cover key areas of the air outlet surface, including the center and edges. The number of measuring points should match the FFU size and evaluation requirements. If you only measure the center point, edge deviations may be missed. If the number of measurement points is too small, the results will not be representative enough.
The measuring plane should also be clear. Whether it is measured near the air outlet surface or at a certain distance from the air outlet surface, the results will be different. The measuring instrument, measuring direction and reading method should also be agreed upon.
After the measuring points and measurement methods are determined, the allowable deviations have corresponding evaluation objects. When the measurement method changes, the allowable deviation cannot be directly applied.
How to agree on working conditions and operating status
The actual wind speed of FFU is related to the operating status. The rotational speed, control settings, filter status and power supply conditions at the time of measurement will affect the results. Measurement conditions should be agreed upon during acceptance, such as rated speed, production mode setting or specified control value.
Filter status should also be agreed upon. The operating points of new filters and dust filters are different. Acceptance is usually carried out with the filter in a clean state, but the filter status and operating time should be recorded.
If the project usesFFU/EFU group control touch screen controller orFFU computer group control system , the control setting values should be recorded during measurement to ensure consistent working conditions.
How to distinguish between mean deviation and local deviation
Allowable deviations can be divided into average deviations and local deviations. Mean deviation describes the difference in average wind speed from the target value. Local deviation describes the difference between each measuring point and the average or target value.
The average deviation can agree on a range, such as plus or minus a few percent of the target value. The local deviation can be determined by a maximum deviation or a minimum wind speed limit to avoid excessively low local wind speed.
If the project has requirements for wind speed uniformity, you can refer toHow to express FFU wind speed uniformity (Note: This link is an example of FFU product page, please refer to the corresponding page on the site for specific uniformity content) to understand the measurement points and deviation expression.
How to agree on retest rules
Retest rules are used to deal with situations where the initial measurement fails or is controversial. The retest rules can stipulate the retest conditions, the number of retests and the judgment method. For example, if the initial measurement fails, you can re-measure it under the same working conditions to confirm whether it is measurement fluctuation. If the retest still fails, the equipment can be adjusted or processed before retesting.
The same measurement method and instrument should be used when retesting to ensure that the results are comparable. The retest record should include the initial results, retest results and treatment measures.
For batch acceptance, the sampling ratio and judgment rules can be agreed upon. If unqualified products are found during sampling, sampling can be expanded or full inspection can be carried out. The specific sampling plan should be determined based on project requirements and lot size.
How to distinguish between on-site system results and equipment results
FFU acceptance usually includes equipment stand-alone acceptance and on-site system acceptance. Single machine acceptance is carried out under factory or on-site single machine test conditions to evaluate the performance of the FFU itself. On-site system acceptance is carried out under operating conditions after installation to evaluate the actual air supply effect and area cleanliness.
The evaluation objects of the two are different, and the allowable deviations should also be agreed separately. Single machine acceptance can be determined based on equipment test conditions, while on-site system acceptance needs to be based on room airflow, return air and operating status. Single-machine test results cannot be directly regarded as on-site system results, nor can only on-site results be used to evaluate the equipment itself.
Issues that should be confirmed in advance during project communication
During the FFU acceptance stage, it is recommended to confirm the following with the manufacturer and the acceptance party: the location and number of measuring points; measurement planes and measurement methods; measuring instruments and calibration status; measurement conditions and operating status; filter status; allowable ranges of average values and local deviations; retest rules and judgment methods; distinction between single machine acceptance and system acceptance; recording format and judgment standards.
If you are developing an FFU acceptance plan, you can visitAili Industrial FFU fan filter unit understands the complete machine configuration, and you can also contact Aili Industrial for acceptance test support.
in conclusion
The allowable deviation for FFU acceptance should be agreed together with the measuring points, working conditions and retest rules. Having only one wind speed target without an evaluation range will cause averages, local readings, and field system results to be mixed together. Average deviation and local deviation should be considered separately, retest rules should be clarified in advance, and single machine acceptance and system acceptance should be distinguished.
Aili Industry has complete production capabilities in FFU complete machine testing and acceptance cooperation, and can explain the measurement conditions and judgment calibers. If you need to know more about the FFU acceptance method, you can visitAili Industrial FFU fan filter unit , you are also welcome to contact Aili Industrial for project support.
