How to convert the 16 bit Digital value into its Physical Value that is in obscuration per foot.
Obscuration per foot is the measure of how a beam of light is obscured by smoke during testing. Our device measures how the light scatters off of smoke present in the optical path; essentially the inverse of obscuration per foot. Where an obscuration measurement would be at 100% signal level with no smoke present (no obscuration), our device would be at 0% signal level since there is no smoke present to reflect off. So it is not as easy as just converting the output of the ADPD188BI into obscuration per foot. Instead, a measurement needs to be made to correlate the output of the ADPD188BI to the obsuration sensor which is measuring obscuration per foot at the same time, and at the same location in the room where the smoke measurement is being made, for example, at the UL facillity.
The output of the ADPD188BI should be converted to PTR (power transfer ratio) which is a value that corresponds to the amount of optical power recieved by the PD vs the amount of optical power provided by the LED. Then during testing you would determine the PTR level for a specific smoke that corresponds to the obscuration per foot measurement made by the obscuration sensor.
To convert the output of the ADPD188BI to PTR use the following conversion:
►PTR = IPD/ILED * (1/PDET_AMPS_PER_WATT) * (1/LED_WATTS_PER_AMP)
How the PTR is related to Obscuration per foot, Can you explain this with an example. and one more thing is i need to convert the Obscuration per foot value to dB/m units.
or else their is any procedure to directly convert the Smoke 16 bit digital value to db/m.
As I mentioned in the above email, our device does not measure obscuration per foot. We measure what is essentially the inverse of obscuration per foot. In order to understand how the output of the ADPD188BI correlates to obscuration per foot, this can only be done by empirical testing. You need to build your smoke detector and test it in the standards facility, e.g. UL smoke labs, so you can empirically measure what the output of the ADPD188BI yields at the obscuration per foot thresholds dictated by the standards.