SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: John
Date posted: Wed Dec 5 13:02:43 US/Eastern 2001
Subject: Momentary Switches
Does anyone have failure rates for mechanical momentary push button switches vs. Hall Effect momentary push button switches? These switches would be used in an industrial environment (sealed from moisture and dust).
Subject: Push Button vs. Hall Switches
Reply Posted by: B.W.Dudley
Organization: Reliability Analysis Center
Date Posted: Thu Dec 6 10:07:20 US/Eastern 2001
In the RAC databases, I found information in the Non-Electronic Parts Reliability (NPRD-95) handbook relating to mechanical push button switches. The environments and applications vary from severe military airborne to ground commercial controlled. The summary rate for commercial application is 0.426 failures per million hours, where the military rate is 4.6 failures per million hours. The ratio of ten to one is partly due to conditions and partly due to the operator misuse. I could not locate data for the “Hall” switches so I searched to see what the differences in construction are. What I found is the major difference is mechanical contacts vs. a CMOS Hall Sensor circuit.
Using the information on failure modes from our Failure Mode/Mechanism Distribution (FMD-97) on push button switches to define the contact and the mechanical button percentages, I determined that 65% of the failures could be attributed to the mechanical button and 35% to the contacts. Therefore, the push button failure rate looks like 0.28 failures per million hours for the mechanical part and 0.146 failures per million hours for the contact part.
From the electronic part data, I estimated that the Hall CMOS sensor has a failure rate of approximately 0.015 failures per million hours. Combining this rate with the mechanical push button failure rate of 0.28 failures per million hours, results in an estimate for the Hall switch to be 0.285 failures per million hours.