High Voltage sampling with MUC

[anishkgt]

Hi All,

I have a project where i need to sample the mains voltage into my MUC (an Arduino) and came up with this schematic of a precision rectifier, attached as CS.

Explanation
Idea here is to detect when the secondary of the Transformer (MOT) is shorted. The LIVE LOAD here is a transformer (MOT) used for Spot welding, when shorted i can a voltage drop from 1.0vac to 0.5vac i just need to send this voltage to the ADC of an Arduino. So here for isolation i used a MOC3052 (https://www.digikey.com/product-detail/en/on-semiconductor/MOC3052SR2M/MOC3052SR2MCT-ND/1847083)optocoupler from fairchild. The LT1078 (https://www.digikey.com/product-detail/en/linear-technology-analog-devices/LT1078S8-PBF/LT1078S8-PBF-ND/889633)is a dual opamp precision rectifier from LT. C24 is a decoupling cap and C25 is to smooth the ac signal from LT. Then the second opamp is a buffer.

Working
The the opto coupler would be triggered by the MUC via 220 \$\Omega\$resistor there by shoring the contact from the LIVE LOAD to the voltage divider and that goes on to send a dc voltage to the MUC. This happens when the MOT is powered.

When the secondary is shorted now there would be a voltage drop at the primary contacts of the MOT and that would also be seen by the LT1078 and using code, the voltage drop would be sensed by the MUC then the the opto coupler would be disabled and the MOT would be powered for spot welding. Basically an Auto Sense, instead of having to press a button to weld.

Then i noticed this schematic from TI, attached (http://www.ti.com/lit/an/sboa097b/sboa097b.pdf) page 4 Fig3 where a similar approach with less components. My basic requirement is to sense the voltage drop at the primary of the MOT.

A silly question but am little confused as to which one to go with. I would really appreciate if somebody could advise/comment on the schematic. With the best of my knowledge and google i guess my schematic would work. I don't have the parts to test this out but before i do i just need some advise.