...
Connect the loopback board to a DOut DB37 connector and connect the cable to a DIn DB37
Connect the loopback board’s Vuser to a power source
Observe the DOut feedback on the DIn using the integration model
For more information about the use of Vuser and Vrtn pleaser refer to this article in the OPAL-RT knowledge base : How to power the different DB37 boards for digital outputs.
AIN and AOUT Loopback Test
...