Some digital pressure transducers on the market today are available with an analog output. Questions often arise about how the signal from the silicon pressure sensor is converted, how the resolution is achieved, how fast the output signal is updated and what form the output takes.
The pressure acting on the sensor mechanically deforms the sensing element. This deformation causes the electrical properties of the silicon Wheatstone bridge circuit to change in a way that is proportional and repeatable, with respect to the temperature and pressure at the sensor. The analog electrical signals from the Wheatstone bridge are passed through a 24 bit analog to digital (A/D) converter.
This digital signal is sent to a microprocessor that interprets the signal based on a characterization algorithm that is unique to each individual sensor. (In an extensive manufacturing process, each sensor / electronics pairing is characterized to ensure the output of the signal from the transducers meets or exceeds its accuracy specification.)
The characterized digital signal then goes to a RS232 or RS485 converter where it is converted to an ASCII string and sent out on demand through an RS232 or RS485 communication port. For a unit with an analog output, this digital signal is also sent to a digital to analog converter where it is turned back into a fully characterized analog signal suitable for transmission into a control or monitoring system.
The resolution of the digital signal output is > 1 PPM. The update rate for the digital and analog output is 50 Hz. Resolution for the analog output ranges from 1 part in 87,000 to 1 part in 870,000, depending on the voltage output range selected.
Below is a flow chart that shows a simplified signal processing scheme: