How should non-integer ISO grades be understood?

Occasionally you will encounter annotations such as ISO 6.5 and ISO 7.5 in projects. People who see it for the first time are often stunned - isn't the ISO grade an integer? Why are there decimals?

It does exist, but it's not a device model or a number you can just add to it. Non-integer levels express a particle concentration control target between integer levels. Projects that use it usually feel that the integer grades are either too loose or too tight, and want to more accurately correspond to their crafting needs.

To understand it, you need to go back to the grading logic of ISO 14644 itself.

where does it come from

ISO 14644-1 classification table, each integer grade corresponds to a set of concentration limits. But these limits are not continuous - there is a gap between ISO 5 and ISO 6.

The requirements for particles in some processes fall exactly into this gap. For example, a certain equipment manufacturer may require that the concentration of particles no less than 0.1 μm should not exceed a specific value. This value is converted into ISO caliber, which corresponds to an intermediate value such as ISO 6.2 or ISO 6.5.

Therefore, non-integer levels are essentially to express concentration limits continuously . a way It is not an extra level in the standard, but an intermediate point deduced from the grading formula.

Once you understand this, you know how to use it.

First confirm why the project uses intermediate goals

Not all non-integer grades are well founded. Some people may have heard a number from their peers, while others may have had strict requirements written into the contract by the equipment supplier.

When you receive a non-integer grade request, ask a few questions: Where does this grade come from? Is it the original requirement in the equipment specification, or is it a reference to a standard document? What are the specific concentration limits and particle sizes behind them?

If the other party can't explain the source clearly and just thinks 'it's safer to be stricter', then the non-integer level may just be decided on the head. In this case, one should go back to the process itself, confirm the actual particle control objectives, and then decide whether an intermediate grade is needed.

If it does come from equipment specifications or customer agreement, then document the corresponding particle size, concentration limits, and test status. These are the basis for subsequent selection and acceptance.

How to do inspection and acceptance

The detection method for non-integer levels is not essentially different from that for integer levels, but the judgment limits are different.

The particle size must be determined first . The non-integer grade itself does not specify the particle size, it is the concentration limit corresponding to a certain particle size. The project document must state: What is the maximum allowed concentration at which particle size? Only write ISO 6.5, the inspector does not know which particle size to judge.

The status should be clear . Static, dynamic or empty? Non-integer levels usually appear in scenarios that require precise particle control. The actual results may vary greatly depending on the state.

The test method follows the standard . Sampling point layout, sampling volume, and instrument selection are still implemented in accordance with the rules of ISO 14644-1. Non-integer levels do not change the test method, only the judgment limits.

The report must indicate the basis for the limit value . In addition to 'reaching ISO 6.5', the acceptance report should also state the concentration limit and particle size corresponding to this grade. In this way, the basis for judgment can be checked during the review.

As mentioned in What is the Difference Between Cleanliness Level and Filtration Efficiency? Space level and filter efficiency are two different things. Acceptance of non-integer levels must also record product information and space test results separately.

Equipment configuration is not directly derived from the numbers

If you get a non-integer level, you cannot select equipment directly based on the size of the number.

The target concentration is the real input . The concentration limits corresponding to non-integer levels are the starting point for equipment configuration. Only by knowing the allowable concentration, area volume, pollution load and air flow pattern can the required air supply volume and filtration efficiency be calculated.

Integer levels can be used as a reference . If the non-integer level is close to an integer level, you can refer to the common configuration scheme of the integer level. However, the final configuration must still be calculated based on the actual concentration target and cannot be directly applied.

Filter selection to see specific data。 The HEPA and ULPA filter pages have efficiency and resistance parameters for different levels of products. When choosing, check the performance of the specific model at the target air volume, rather than just looking at the grade name.

The air supply equipment must match the working point . The resistance of the filter will affect the fan operating point. The FFU clean air supply product page has interface instructions for standard products and customized solutions. For local purification on the equipment side, please refer to EFU equipment side fan filter unit。

The control system is configured by zone . If the level requirements of different areas are different, the control system must be able to be adjusted by zone. The FFU group control system can configure operation strategies by region and time period.

Aili Industrial has manufacturing capabilities in motors, fans, control systems, sheet metal, air filters and complete machine assembly. When working on non-integer level projects, you can check the target concentration, filter resistance, fan operating point and structural interface under the same project conditions to ensure that the equipment configuration and limit requirements are consistent.

What to write in the contract

There are a few points to note when writing non-integer levels into the contract.

State the grade and corresponding limits . Simply writing ISO 6.5 is not enough. You must also list the particle size and concentration limits corresponding to this grade. Conversions from different sources may be slightly different, so writing them clearly can avoid disputes.

Indicate the source of the citation . If the rating is from an equipment specification or industry standard, indicate the document number and version. When doubts arise later, the evidence will be available.

States and regions are listed separately . The conditions under which non-integer levels are measured and which area they correspond to should be clearly stated.

The acceptance method is agreed upon together . Testing standards, sampling methods, and judgment rules are specified in the contract. How do hundreds, thousands and ten thousand classes correspond to the complete expression method mentioned in ISO grades? The same applies to non-integer grades - standard, particle size, state, area, none of them can be missing.

Scene judgment

A semiconductor equipment manufacturer requires in its equipment specifications that the concentration of particles no smaller than 0.1 μm inside the equipment should not exceed a specific value. Converted to ISO caliber, it roughly corresponds to ISO 5.5.

The project team did not directly configure the equipment according to ISO 5 or ISO 6, but used the original concentration limits in the equipment specifications as input, calculated the air supply volume and filtration efficiency of the target area, and verified the available space inside the equipment. The final configured EFU meets the limit requirements under the target air volume.

Another project saw ISO 6.5 in the contract, but the particle size and status were not stated. During the acceptance inspection, the two parties had inconsistent understandings of the test conditions, and the technical agreement was later supplemented to resolve the issue.

These two situations illustrate that the understanding of non-integer levels must fall on specific concentration limits and test conditions.

Key points for selection and acceptance inspection