PULSE WIDTH DEMODULATED
The SMT-9700 product is based on eddy current inductive technology. This product relies upon impedance variation in the sensor coil, and detection and demodulation in a phase detection circuit (based on pulse width modulation techniques - PWM). The system consists of a sensor, a signal conditioning electronics with an integral DC input and system voltage output cable (I/O cable), and a separate interconnection cable (when not integral with the sensor).
System benefits: Small, OEM configurations, excellent resolution, and only single-ended power supply required.
The proprietary PWM technique used in the SMT-9700 circuit allows for extraordinary low system output noise. Typically, an analog system is full of op-amps with their inherent noise, but since this highly sensitive PWM system does not require a high gain op-amp, there is very low noise. The noise that is present is almost "white" in character (approximately equivalent to the thermal noise of a 50kW resistor) and diminishes as the bandwidth narrows towards DC. This system can be optimized for temperature stability or linearity.