The implementaion of the frequency and voltage sensing individually was stright forward as described, but trying to combine the 2 circuits from one 9 vac (wall wart) and rectifier bridge power supply created a problem, that probably requires an opto-isolator on the frequency side. The frequency side requires the rectifier bridge "+" output to go to the PLC's power in (12 VDC in my case). For voltage side, I prefered the bridge "-" output go to the PLC's ground terminal, assuming the ADC voltage in/output reading is fairly close to linear, then calibration only requires one voltage (120 VAC) checked with a voltmeter, and a simple equation in Basic to correct the readings. Then we have the rectified 9 VAC connected across 12 VDC which just doesn't work. I have stock of a TIL 111 opto isolator that will try to interface.