I put the non delayed signal into an attenuator box, by using the dial you can change the amplitude of this helicity signal from 100 % to 1 % and I fanned this signal with a constant voltage of about -500 mV. If this signal is sent as BCM signal that should produce some asymmetries in all the DAQ so I let Pengjia inject the signal where needed. Not sure if the signal need to be positive or negative this can be adjusted with the linear fan offset.
Pengjia should double check the cabling in case I miswired the fibers while testing and looking at the scope by eye it did not look delayed by 8 windows, so check the helicity board setting and output.
The asymmetry should be : attenuated helicity amplitude / DC level.
If you could take runs with different known asymmetry and plot BCM asymmetry for scalers and HAPPEX for different known value that will be a good cross check. i think T8 with a prescale of 10 or any trigger with a rate of a few hundred hertz should do.
Once checked we can consider giving our simulated helicity signal to Hall C during beam study to check we all find the same asymmetry.