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BTLE Sensor generates readings without being connected to my ear (aka: Ghosting)

Apr 05, 2018

The issue referred to as “ghosting” is the result of feedback from the aggressive automatic gain function created by our engineers to deal with a wide range of pulse strengths and skin types. All efforts to prevent it led to reductions in sensitivity. 

The problem with “ghosting” is related to a number of factors. To capture HRV, our devices work at much higher sample rates than typical averaging heart rate monitors and SPO2 devices. Standard average devices sample at 20 - 40 samples/sec. We sample at a minimum of 125 samples/second. The higher frequency provides more opportunity for random beat frequencies to be established.

When in contact with a body part, there isn’t any real back ground signal to eliminate. We essentially work in a closed loop condition. To deal with the widest possible range of skin types and pulse strength, the sensor aggressively tries to find the optimum signal strength by boosting LED output using PWM (pulse width modulation), while the input analog stage adjusts the gain across 32 possible amplification settings.
It might even result as appearing “coherent” from an HRV perspective and continue to record.

This is a normal response from the electronics in the BTLE sensor. It in no way harms the unit nor does it make it defective. As soon as you place the sensor on your ear, it will begin registering your actual pulse, acquire 64 seconds of data and go back to displaying current session data.

 




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