Letter 37045

Reliability of silver contacts in relay pressure switch  

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Hi, I am trying to figure out whether silver contacts are reliable enough over time for a relay switch we're using or we need to use gold contacts. The switch is going to be used in a 5V circuit as logic control and will bear ~10mA load when it's on. Since the switch serves a failsafe purpose it will be pretty much always off unless something goes wrong (over pressure in the system). The trigger point of the pressure switch is about 6psi and the device is a medical device that will be used in controlled environments such as hospitals or physicians office. We are aiming for a 7 year lifetime for the device (and thus the switch).

I've read that silver tarnishes over time especially at low currents, or when switching action is absent. but I've always read that there needs to be sulphur in the environment for silver oxidation to occur, and that silver oxide is also conductive.

anyone has opinions on whether silver contacts could stay reliable for 7 years in a controlled environment in this application?


thanks much,

Ethan Kung
VSM MedTech - Coquitlam, BC, Canada

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