Photocapacitors and Photodetectors

A: That’s the most common mistake — treating the window as if it controls what happens inside the junction. The window only attenuates or blocks incident photons. Once UV has already been admitted for years, lattice damage in the photodiode continues regardless of window integrity. Cracking changes transmission and angular response, which explains missed flames or nuisance trips, but it doesn’t arrest junction-level degradation.

A: That’s where people trip — assuming all capacitors on a P&ID are polarized. Photocapacitors used as integrators are typically symmetric structures. A polarized symbol implies electrolytic behavior that simply isn’t there, and it changes how maintenance interprets polarity and failure risk. The other items are annoyances, not drawing errors.

A: That’s the usual slip — mixing photon energy with responsivity units. Start with power: 0.5 mW/cm² over 0.1 cm² gives 0.05 mW incident. Multiply by 0.15 A/W and you’re in single‑digit microamps. Capacitance affects bandwidth, not DC current, and photon energy is already baked into the responsivity.

A: That’s the confusion between capacitive storage and resistive sensors. Photocapacitors integrate photocurrent, so more light means a steeper ramp, not a step. The fix is in signal interpretation, not hardware damping, otherwise you’ll hide real transients.