Tool/software:
Hi Forum,
I am currently testing an ultrasonic flow meter for water using a W configuration on a 20mm copper pipe. The acoustic length of the configuration is around 75 us, which is so long that the Rx bias switches off just before the signal is received. In the ADC capture this is seen as a offset at the beginning of the capture:
I know this is due to the Rx Bias, as I analyzed the signal over the input capacitor with an oscilloscope. The same capture above is shown in the red box in the image below:
In order to make the Rx bias last longer, I have tried the following:
- Modified the USS_PGA_IN_BIAS_COUNT_SEC and Start PGA and IN Bias Count (ns) parameters in the software library and GUI. In the software the program "breaks" (no impulses are sent), and in the GUI only a maximum value of 99 is allowed before the program also breaks (no ADC capture possible). According to my calculations, I would need at least an extra off set of 50 us, so I would need to be able to enter a value of at least 50000.
- I have tried moving the PPG impulses forward by using changing the default USS_START_CAPTURE_SEC value from 1.0E-5f to 0.0, however this would only give me an offset of 10 us.
- Modified all ASQ (Acquisition Sequencer) Timer values (GENERIC_SAPH_ATM_A, GENERIC_SAPH_ATM_B, GENERIC_SAPH_ATM_C, GENERIC_SAPH_ATM_D, GENERIC_SAPH_ATM_E, GENERIC_SAPH_ATM_F), however I never managed to offset the end of the Rx Bias. In theory I would just need to modify GENERIC_SAPH_ATM_C which is the register that takes USS_PGA_IN_BIAS_COUNT_SEC as a parameter and as I previously mentioned this just breaks the program.
- I have tried modifying the USS_ULP_BIAS_DELAY parameter, however this only modifies the beginning of the Rx Bias, not the end.
- I am currently trying to control the capture manually using register mode, however this is pretty complicated and I couldn't find any code examples that show how this is done.
How can I increase the time of the Rx bias, in relation to the the PPG impulses so that the signal is received before the Rx bias ends? According to the documentation, it should just be as simple as modifying the USS_PGA_IN_BIAS_COUNT_SEC and Start PGA and IN Bias Count (ns)parameters, however this doesn't seem to do anything.
Many thanks,
Jonny