REG NASA-LLIS-0413-1996 Lessons Learned - Incorrect Actuations of Relays in Matrix (1975).pdf

1、Lessons Learned Entry: 0413Lesson Info:a71 Lesson Number: 0413a71 Lesson Date: 1996-06-26a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Incorrect Actuations of Relays in Matrix (1975) Abstract: Because the Viking Orbiter power switching relays were arranged in a matrix, two r

2、elays could under certain conditions be inadvertently actuated when only one was commanded. A system control protocol should be established whereby independently requested relay actuations are executed in a predictable manner.Description of Driving Event: (Relevant Historical Lesson(s) Learned)Under

3、 certain conditions, the Viking Orbiter (VO)75 power switching matrix permitted two relays to be actuated inadvertently when only one was commanded. This occurred twice during system test at Eastern Test Range, causing potentially detrimental state changes.The power switching relays were arranged in

4、 a matrix. Actuation of a relay required enabling the correct column (source) and row (sink). The desired relay was actuated because only one relay corresponded to a given row and column. However, when two relays are commanded simultaneously, two columns and two rows are enabled at the same time, pe

5、rmitting up to four relays to be actuated. Diode isolation reduced this number to three.On VO-75, when the battery was fully charged, the design provided for a power relay command to be automatically sent to reduce the charge rate to a low level. The test team was commanding other relays in the matr

6、ix, not anticipating the automatic battery charge command. On two occasions, these commands arrived simultaneously, causing a third relay to be actuated inadvertently.Additional Keyword(s): Ground OperationsProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS

7、-,-,-Reference(s): VO75 P/FR No. 34874; 35304Lesson(s) Learned: Relay matrices should be designed to prevent actuation of additional relays caused by multiple relays being commanded simultaneously.Recommendation(s): N/AEvidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/A

8、Mission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1995-08-10a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-