There isn't a great deal of difference, except that propinquity can imply a psychological or emotional closeness, as well as physical, that proximity is not usually used for.
The meteor's propinquity gave astronomer's cause for alarm because of it's proximity to the earth's surface .
We ambled down the path, unaware of the propinquity of the danger that lay ahead.
Remoteness
Propinquity, the state of being close to someone or something; proximity, is the single greatest influence on marital homogamy.
go to dictionary.com and enter propinquity.
It's a bit complex, but in general it means the tendency for people to form bonds with other people who are like them in some way, or with whom they have more frequent contact. It can refer to more frequent physical contact or closeness, two people living on the same floor of a building for example, or to similarities in terms of beliefs or interests.
his propinquity to danger filled him with trepidation
A limit switch turns on or off when the object being sensed reaches a specific location.A proximity sensor returns an analog signal indicating how far the object is from the sensor.
Synonyms: togetherness, closeness, similarity, relations, connection, kinship etc. Antonyms: distance , difference, separated, remoteness, faraway.
photoelectric sensor-sense both metal & non-metal proximity sensor -sense metal only
Income items and expenses differ on many fronts, but they also share conceptual proximity in some situations
Here is a link that will answer your questionhttp://www.automationdirect.com/static/specs/proxterms.pdf