During a design review yesterday, a question was posed to me about whether or not the customers will need to use gold contacts on the switches that connect to our system. In response, I have been searching for some guidelines as to when gold contacts are required. I have found a lot of information discussing mechanical operation of contacts, wetting current, oxide build up, etc, but have not found anything providing some "rule of thumb" recommendations.
In this instance, the design is as follows:
Our design contains (user) inputs implemented with opto isolators. The circuit design is such that we provide a 12V signal and ground and the user provides a switch closure to flow current from the 12V supply through the opto's diode and a current limiting resistor. I can't control how far away the switch will be located or what type of switch the customer will use. I can control the size of current limiting resistor, which I present have set as 1.2K for 10mA of current @ 12V through the opto.
My question is does anyone have any rule of thumb that says, generally, under X volts or X amps, gold contacts are required. I understand that this is a vague question and an exact answer depends on the application, environment, etc, and information I don't (and won't) have.