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Principle of Mass Flow Instruments
- 5. Definition of specifi cations
- The indication of mass flow instrument specifi cations in this taxt basically conforms to the SEMI standard. The defi nitions of representative specifi cations are explained below.
(1) Accuracy
The accuracy is indicated in the form of"Full scale ±%."This is the % value with respect to the full-scale value of the error when the calibration standard gas (N2, for example) is used for our standard fl ow meters. Therefore, when the accuracy is ±1% in the range of Full-scale 50 SCCM, the flow rate will be guaranteed with the uncertainty" of 50 x (1/100) = ±0.5 SCCM with respect to our standard flow rate.
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(2) Repeatability
The form of"Full scale ±%"is the same as the accuracy.
This value indicates the deviation of the value obtained by measuring the flow, which is set under the same environmental conditions,with our standard flow meters.
This definition is different from the reproducibility that shows the deviation of the value after the environmental
condition is changed.
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This value indicates the deviation of the value obtained by measuring the flow, which is set under the same environmental conditions,with our standard flow meters.
This definition is different from the reproducibility that shows the deviation of the value after the environmental
condition is changed.
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(3) Response
The response is indicated by the time taken for the output of mass flow instruments to stabilize at 98% of the full scale after starting control from zero flow.
Such indication is adopted usually because it is diffi cult to analyze 100% in the case of an asymptotic line.
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Such indication is adopted usually because it is diffi cult to analyze 100% in the case of an asymptotic line.
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Note
The value used to indicate the fl ow range is the full-scale
(100%) value only when N2 (or air) is made to flow.
Therefore,when the type of gas and pressure conditions are different, even if the fl ow is the same, we may not be able to manufacture products according to the desired specifi cations; please contact us in advance.
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(100%) value only when N2 (or air) is made to flow.
Therefore,when the type of gas and pressure conditions are different, even if the fl ow is the same, we may not be able to manufacture products according to the desired specifi cations; please contact us in advance.
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