Hi Eric
Thanks for running the simulation. So its a window comparator ie a discriminator circuit but what does it discriminate between. So based on Va and Vb it looks like a delay circuit of 350ms if the U3 and U4 comparator volts are set as you show on your diagram.
I have tried to understand each part and so far see the first rectifier bridge as redundant as it seems to do nothing?
The U1 and U2 seem to give out a square wave at the same frequency as the AC line frequency
Then it appears to convert it to DC and filter it?
Do you think it could be to detect the rate of change of the 120v AC line?
I will try to get the other half posted later today.
Thanks
Q