rezabejd
May 10th, 2006, 02:32 PM
Curious if anyone has run into an issue with "wetting current" and FF discrete inputs. That is, for example, normal silver-cadmium contacts develop an oxide layer that eventually becomes an open circuit as seen by DC interrogation voltages (e.g. 24 VDC) - because the small milliamps available do not "scour" the oxide layers like higher voltages do.
Since a great deal of the switches we use are already "hermetically sealed" - and presumably less vulnerable to oxide formation / corrosion, maybe this is rarely a concern.
I have an application where the vendor is using a pressure switch to open the Ff device's signal to a piezo solenoid; a brute force way of making a double acting actuator have a fail position on loss of instrument air. Do you think I should insist on gold plated or hermetically sealed contacts for these applications?
Prost!
John Rezabek
ISP
Since a great deal of the switches we use are already "hermetically sealed" - and presumably less vulnerable to oxide formation / corrosion, maybe this is rarely a concern.
I have an application where the vendor is using a pressure switch to open the Ff device's signal to a piezo solenoid; a brute force way of making a double acting actuator have a fail position on loss of instrument air. Do you think I should insist on gold plated or hermetically sealed contacts for these applications?
Prost!
John Rezabek
ISP