SBOU024C august 2004 – july 2023 PGA309
The over-scale and under-scale limit circuitry combined with the fault monitor circuitry provides a means for system diagnostics. A typical sensor-conditioned output may be scaled for 10% to 90% of the system ADC range for the sensor normal operating range. If the conditioned pressure sensor is below 4%, it is considered under-pressure; if over 96%, it is considered over-pressure.
The PGA309 over/under-scale limit circuit can be programmed individually for under-scale and over-scale that clip or limit the PGA309 output. From a system diagnostic view, 10% to 90% of ADC range is normal operation, < 4% is under-pressure, and > 96% is over-pressure. If the fault detect circuitry is used, a detected fault will cause the PGA309 output to be driven to positive or negative saturation. If this fault flag is programmed for high, then > 97% ADC range will be a fault; if programmed for low, then < 3% ADC range will be a fault. Now the system software can be used to distinguish between over- or under-pressure condition, which indicates an out-of-control process, or a sensor fault.