Not quite sure what you're trying to do there, but it looks like there's a lot wrong.
1) You've got a diode in series with sensor output which will allow only negative signals through, but your opamp is referenced to ground. I think you want to turn that diode around and maybe put a resistor to ground on the opamp input.
2) Your opamp is open loop; what you want is a comparator with some hysteresis.
3) You're using a resistor and two diodes to (presumably) set the negative input to 1.2 V. Why not use a resistor divider?
4) What's up with the resistor and zener on the output? You've got a 5volt supply on your opamp, and a 5.1 volt zener. Do you expect your opamp output to exceed 5v?(Hint: it won't)