In the product I analyse (an optical fork sensor, rated 10V-35V), there is a sizewise big capacitor between ground and chassis.
I measured its value with an LCR meter, it is 60nF. I also broke one by accident, which revealed a liquid from inside. Looking at its size and considering the liquid inside, I think it is a film capacitor.
1) Why is there a capacitor between ground and chassis? For EMI purposes? (Note: the cables used for this product are usually not shielded - chassis is floating if there is no capacitor)
2) Why is the capacitor a metallized film type? (if it is) It seemed to me like a ceramic capacitor may also have been used in this scenario - it has a smaller footprint.