When the input signal Vin is positive, Op-Amp output terminal is negative, Diode D1 is reverse biased and D2 Diode is forward biased, the circuit is Vb = - (R2/R1) * Vin In the circuit, R1 and R2 have ...

With a reference-clip from both probes (channel 1 and 2) connected I’m actually shunting around one of the diodes, effectively turning the bridge back into a half-wave rectifier.