The following report was received via fax:
On June 4, 2015, Rotork Controls Inc. opened a formal Part 21 [10 CFR 21.21] investigation into a self-identified anomaly relating to a basic micro switch - Pt No N69-921, description 'V12'. The anomaly is intermittent variation in electrical contact resistance and was first observed during the factory acceptance test of a Rotork safety related NA Range Electric Actuator; also referred to as an electric Valve Operator.
Rotork and the switch manufacturer are currently characterizing switch population contact resistance to establish whether an unsafe condition could exist as defined under 10 CFR 21.
- * * UPDATE AT 0958 EDT ON 9/10/2015 FROM PATRICK SHAW TO MARK ABRAMOVITZ * * *
The following report was received via e-mail:
Rotork has concluded the investigation and based on test data determine an unsafe condition can exist as defined under 10CFR21. Testing has established that a small percentage of the switches supplied against Rotork purchase order P0116932 may exhibit an open circuit condition when operated. A slightly larger percentage of the population may exhibit high contact resistance ranging from 0.5 Ohm to open circuit. The anomaly affects the normally open and normally closed contacts equally. Contact resistance anomalies are random, not permanent, and appear to be unaffected by accumulated cycles. Additionally when a switch is operated its electrical state remains constant until the next operation.
Probabilities have been established by resistance measurements and by dynamic testing using voltages representative of customer applications. The dynamic evaluation predicts an open circuit probability of 0.0008% per operation. To date, no switch failures have been reported from any customer sites. Below are listed all orders provided to customers containing V12 switches from the defect batch. Report ER791 provides full details of Rotork's technical investigation.
Notified the R1DO (Gray), R2DO (Shaeffer), R3DO (Pelke), R4DO (Drake), and Part-21 Group (via e-mail).