The DA660 uses Electrodynamic technology, an advanced rod electrifi cation method. The DC signal created by particles colliding with a probe inserted in a stack duct is electronically filtered out, leaving a conditioned AC signal resulting from charged particles passing and interacting with the rod. Since the signal includes no DC component, the instrument has minimal cross sensitivity to changing velocity and has increased stability even with dust build-up on the sensor rod. The dust signal is amplified, digitised and processed at the sensor, consistent with good signal to noise design techniques. The processed signal is proportional to dust concentration although the exact correlation is application dependent.