The Surface Reference Pickoff (SRP) is a simple and versatile sensor for metal gear positive displacement flow meters. Internally, an oscillating circuit produces a carrier frequency in the pickoff coil. The ferrous gear teeth of aPD flow meter modulate the amplitude of the carrier.
The modulated signal is then filtered and amplified to produce a square-wave pulse. The SRP is recommended when the desired output signal is a square-wave pulse and a DC supply voltage is available.