Electrical – Meaning of micro-sd card symbols

A "voltage reference" is a device that provides a precise voltage to be used as a calibration source, in this example the + input of the op-amp (adjustable in this case using a potentiometer).

When a potentiometer is included, it is usually a precision one with 10 or 20 turns, and a test point would be provided on the wiper lead to measure the voltage with a digital voltmeter as the pot is adjusted.

References are different from power supply rails (e.g. 5v or 3.3v) in that the voltage is more tightly controlled, and is not subject to the spikes that usually show up on voltage rails. They usually have a limited output current, such as 10 ma..

Here is an example of a family of voltage references that includes a 10v source with a 0.1% accuracy. Note some of the values look odd, such as 2.048v and 4.096v; these are designed to provide a voltage reference for devices like a DAC, which may have 11 or 12 bits, and thus map directly so 1 bit equals 0.1 mV.

You could try loading a dummy card while coating to act as a mask for the contacts. In my experience, SD cards themselves are quite hardy to moisture but unless you seal the SD card into the socket you'll have a potential for water ingress to the contacts. I've only dealt with conformal coatings a few times and usually the boards only have pigtails to avoid this sort of issue with connectors.

That said, I have potted boards with connectors installed for prototype systems and the epoxy never broke the contact. You might be fine installing the final SD cards prior to coating as long as you don't intend to access/remove them.