Predictive maintenance & condition monitoring


synchronise separate, and usually similar, ADCs with each other. In time-sensitive ADCs, this typically comes with the requirement to have the SYNC pulse in sync with the sha red controller clock (MCLK). Otherwise, the synchronisation trigger of one device may be one MCLK period delayed from the others due to jitter and propagation delays. Figure 12 shows how each ADAQ776x-1 can be synchronised using a SYNC_IN pulse from a controller, ideally tracking with the system MCLK.


Figure 11. Various ADAQ776x-1 generics used with IEPE sensors.


Due to the synchronisation and phase matching requirements in CM applications, the ADAQ776x- 1 and AD7768-1 generics include a SYNC_OUT pin that outputs a SYNC_OUT pulse when triggered by a GPIO = START input pulse, or through an SPI write. In both cases, the SYNC_OUT pulse can then be fed into the SYNC_IN pin, triggering the start of a valid data conversion. To reduce the number of isolated digital lines in channel-to-channel isolated systems, it is recommended to use Method 2 where synchronisation can be achieved by initiating a SYNC_OUT pulse through an SPI write to all devices from the same SPI input line (SDI), as shown in Figure 13. This assumes a common MCLK across channels, that is ideally synchronised with the SPI clock (SCLK) to avoid delayed triggering. This implementation eliminates the need for an isolated SYNC_IN or START line from the controller. Further reducing digital isolation lines, the ADAQ776x-1 and AD7768-1 generics can combine the data ready signal (DRDY or RDY) with the output data (DOUT) in the same line. A channel-to-channel isolated high performance DAQ solution using the ADAQ7768-1 is shown in Figure 14. It uses the ADP1031 as its isolated power solution, powering up all the supply rails, plus a ADuM141D for additional isolated digital lines.


CONCLUSION


A CM system comprised of isolated single channels of the ADAQ776x-1 is a cost-effective solution that delivers a phase matching performance comparable to simultaneous


sampling SD ADCs. µModule solutions tackle the phase matching problem introduced by the RC anti-alias filters with the precise resistors provided by ADI’s iPassives technology.


Figure 12. Synchronisation of ADAQ776x-1 devices in channel-to-channel isolated systems using a SYNC_IN that tracks with MCLK.


Analog Devices www.analog.com


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Figure 13. Synchronisation of ADAQ776x-1 devices in channel-to-channel isolated systems using an SPI write.


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Figure 14. Channel-to-channel isolated high performance DAQ solution using the ADAQ7768-1.


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October 2024 Instrumentation Monthly


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