Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1088111
Healthy Indoors | 33 struments is critical in ensuring that these instruments per- form as expected throughout their lifetime. Below is an actual calibration histogram plot from a production instrument running 0.3um calibration particles. On this plot we can see the system noise in the bump to the left of the red line. The calibration peak for the 0.3um particles is near the green line and the width of this peak is measured between the blue lines. The signal-to-noise for this plot is the ratio of counts from the green line to the red line which works out to 112:1 (the standard requires that it be > 2:1) and the size resolution (roughly the width between the blue lines) is 8.8% (the standard requires that one channel be < 15%). To get this kind of performance is non-trivial and all the established particle counter suppli- ers that meet this standard spend significant engineering efforts just meeting the standard. But, the ISO 21501-4 calibration process greatly improved the accuracy and consistency of these instruments and be- cause of this compliant instruments track very similarly. For ex- ample, the plot below shows two instruments that came off the calibration bench and were setup to sample room air (with a Y-tube ensuring they sampled from the same air stream). We can see that these track very well on a channel-by-channel basis, we also find that instrument that were calibrated months For cleanroom applications this is important since these instruments are often used to control important process- es and they want to ensure the instrument they use to do so can be relied upon. Of course, specifying a calibration interval doesn't ensure that, but ideally the interval is spec- ified by the manufacturer such that there is a high likeli- hood that the instrument will remain in good working order throughout that period. For air quality applications there is significant pressure in creating instrumentation that doesn't require re-calibration. In such instruments then it would be important to provide an expected lifetime figure or some means of running internal tests to validate operational health. 11. Test report This requirement states that a calibration report should be included with the instrument with the results of most of the above requirements. For cleanroom applications this is often critical since they often have to provide traceability for all instruments they use in their process, so there are often specific requirements they need to see on their calibration reports. For air quality applications this seems less critical, though ensuring that a solid calibration regimen underpins these in-