SLASEC8B February 2017 – January 2019 PGA460-Q1
The system diagnostics in the PGA460-Q1 device help characterize the transducer element during the burst itself and determine the status of the overall system. By using the provided information the system should be able to detect transducer failure, driver-circuit failure (transformer failure if used), environmental effects on the system (such as ice, dirt, snow), objects compromising the transducer operation (such as pressure applied to the transducer), and others.
Three implemented system diagnostics are available in the PGA460-Q1 device that provide information which can be used in detecting system flaws. These diagnostics are described as follows:
Prior to bursting, the comparator output is expected to be low. In the event that the output is stuck high, the condition is detected and the diagnostic fail flag is set
To measure the transducer frequency, a start parameter, FDIAG_START, and a window length parameter, FDIAG_LEN, are defined in EEPROM memory. The start parameter, FDIAG_START, defines the time when the frequency measurement starts relative to the end of the burst time. The diagnostic window length parameter, FDIAG_LEN, sets the time width of the diagnostic window in terms of signal periods captured. A brief example of parameter configuration can be explained:
An additional frequency error feature is implemented in the PGA460-Q1 device to signify that the measured transducer frequency is outside of the limits set by the FDIAG_ERR_TH threshold parameter. The result of this feature is reported in the status frames of the IO time-command or the UART interface. For more information on reporting the transducer frequency error, see the Interface Description section.
The decay period time is measured at the output of the digital data path. The measurement starts at the same time when the burst stage is completed and the decay period is measured as long as the echo level is higher than a saturation threshold level defined in the EEPROM by the SAT_TH parameter. The provided result can be extracted by using any of the PGA460-Q1 interfaces, while the value is expressed in 16-µs time increments. If the decay time measured greater than 4 ms, the value extracted will read 0xFF.
During the noise-level measurement, the PGA460-Q1 device executes the LISTEN ONLY (Preset2) command (see the Interface Description section for details of the command) where no burst is performed but only a record interval is started and lasts 8.192 ms. During this record interval, the data collected at the output of the digital data path is averaged into two groups each containing 4096 samples. The final noise level is measured by performing the noise-level measurement function is the higher averaged value of the two groups. This value is reported as the final noise-level measurement.
The nonlinear scaling block is always disabled (scale factor EEPROM by setting the SCALE_K bit 0 and the NOISE_LVL bit to 0) during the noise-level measurement process.
Figure 11 shows the system diagnostics implemented in the PGA460-Q1 device as a full object-detection record cycle example. The numbers 1, 2, and 3 in Figure 11 show voltage diagnostic, transducer frequency, and decay-period measurement, respectively.