Welcome to the element14 community. There have been a lot of conversation here on this same topic. Like jw0752 mentions above, PIR sensors in and of themselves do not discriminate the source of heat they are seeing. There are some ways that a standard PIR sensor could give you some more information about a source, but most PIR motions sensors are designed to look only at large changes in heat.
Having said that, there are some ways to get more information. One is to use a comparative approach, where the PIR sees a reference signal and compares it to the potential human signal. I have seen this done where a shutter is placed inline with the field of view. The shutter is a wheel like structure that is 50% open (to view the heat source in question) and 50% closed to sense an ambient condition that rotates, periodically obscuring the PIR detector. The electronics compare the live to ambient signal to develop a difference level (think of a sinusoidal waveform where the peak to peak voltage is difference value). This level could be used to determine the strength of the heat source. Too low or too high of a signal would imply a non-human heat source, where a signal between the extremes might be more likely to imply a human heat source. The gain of the circuit would need to be determined such that the human temperature range was always near the middle of the reading range. This approach does suffer in that it is very sensitive to the distance the human heat source and the PIR sensor, i.e. sensitivity decreases as the distance increases.
Welcome to the element14 community. There have been a lot of conversation here on this same topic. Like jw0752 mentions above, PIR sensors in and of themselves do not discriminate the source of heat they are seeing. There are some ways that a standard PIR sensor could give you some more information about a source, but most PIR motions sensors are designed to look only at large changes in heat.
Having said that, there are some ways to get more information. One is to use a comparative approach, where the PIR sees a reference signal and compares it to the potential human signal. I have seen this done where a shutter is placed inline with the field of view. The shutter is a wheel like structure that is 50% open (to view the heat source in question) and 50% closed to sense an ambient condition that rotates, periodically obscuring the PIR detector. The electronics compare the live to ambient signal to develop a difference level (think of a sinusoidal waveform where the peak to peak voltage is difference value). This level could be used to determine the strength of the heat source. Too low or too high of a signal would imply a non-human heat source, where a signal between the extremes might be more likely to imply a human heat source. The gain of the circuit would need to be determined such that the human temperature range was always near the middle of the reading range. This approach does suffer in that it is very sensitive to the distance the human heat source and the PIR sensor, i.e. sensitivity decreases as the distance increases.
