ENS 50096
ENS Event | |
|---|---|
06:00 May 7, 2014 | |
| Title | Part 21 - Potential Defect in Nus-710Du Trip Unit to Produce a Valid Trip Output Signal |
| Event Description | The following summary was provided by Curtiss-Wright Flow Control Corporation:
In certain operating configurations, NUS-710DU Trip Units could fail to produce a valid trip output signal. Transistor Q8 on the referenced units uses a TO-66 package and is flush mounted on the component side of the PCB. The TO-66 package, based on JDEC drawing TO-213 does not specify the size of the glass-sealed holes in the case (collector) around the base and emitter leads. Random samples measure approximately 0.11" in diameter. The PCB includes standard 0.100" solder pads on both non-component and component sides. During manufacture, Q8 is secured using screws and nuts with leads centered in the through-holes, so no direct solder pad to case contact is possible. However, the presence of the pad on the component side could facilitate, under certain conditions, excessive solder flow, creating a close proximity, or in the extreme case bridging, between solder on the emitter or base solder pad and the Q8 case. Permanent bridging would be detected during acceptance testing. However, in at least one case, with the trip unit mounted in the trip unit chassis via an extender card, the proximity was close enough to create contact when the board was slightly flexed. The trip units have two modes of operation, NORM and REV, selectable by switch S2, and four operating configurations: (1) NORM mode, rising trip, energize on trip, (2) REV mode, falling trip, energize on trip, (3) NORM mode, falling trip, de-energize on trip and (4) REV mode, rising trip, de-energize on trip. In configuration (1 ), the set point is applied to the negative terminal of a comparator and the input is applied to the positive terminal. When the input rises above the set point, the output of the comparator goes to the positive rail, turning on Q7. When Q7 turns on, it pulls the base of Q8 low, causing Q8 to turn on. When Q8 turns on, the trip output goes to approximately +24V. In configuration (2), the set point is applied to the positive terminal of the comparator and the input is applied to the negative terminal. When the input drops below the set point, the output of the comparator goes to the positive rail and turns on Q8, resulting in a trip output of approximately +24V. In configurations (1) and (2), bridging at Q8 would cause an output trip signal. In configuration (3), when the input drops below the reset point, the output of the comparator goes to the negative rail, which causes Q8 to turn off. When Q8 turns off, the trip output goes to approximately zero volts. In configuration (4), when the input rises above the reset point, the output of the comparator goes to the negative rail and turns off Q8, de-energizing the unit output. In configurations (3) and (4), bridging at Q8 would prevent a valid trip signal from being generated by keeping the output at logic high. Plant: Limerick/Part Number: NUS-710DU0TS/Quantity: 2/Serial Numbers:1303582, 1303583 Plant: Limerick/Part Number: NUS-710DU0TT27000/Quantity: 6/Serial Numbers: 1304197, 1304198, 1304199, 1304200, 1304201, 1304202 Plant: Columbia/Part Number: NUS-710DU0TT45059/Quantity: 5/Serial Numbers: 1303632, 1303633, 1303634, 1303635, 1303636 Plant: Grand Gulf/Part Number: NUS-710DU0TT27000/Quantity: 3/Serial Numbers: 1303672, 1303673, 1303674 Plant: Perry/Part Number: NUS-710DU0TT27000/Quantity: 33/Serial Numbers: 1304219, 1304220, 1304221, 1304222, 1304223, 1304224, 1304225, 1304226, 1304227, 1304228, 1304229, 1304230, 1304231, 1304232, 1304233, 1304234, 1304235, 1304236, 1304237, 1304238, 1304239, 1304240, 1304241, 1304242, 1304243, 1304244, 1304245, 1304246, 1304247, 1304248, 1304249, 1304250, 1304251. Should you have any questions regarding this matter, please contact Robert Queenan, Division Manager, Scientech/Instrumentation and Controls, at (208) 524-9311. |
| Where | |
|---|---|
| Scientech Idaho Falls, Idaho (NRC Region 4) | |
| Organization: | Scientech |
| Reporting | |
| 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
| Time - Person (Reporting Time:+32.95 h1.373 days <br />0.196 weeks <br />0.0451 months <br />) | |
| Opened: | Vincent Chermak 14:57 May 8, 2014 |
| NRC Officer: | Steve Sandin |
| Last Updated: | May 8, 2014 |
| 50096 - NRC Website
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Scientech with 10 CFR 21.21(d)(3)(i), Failure to Comply or Defect | |
WEEKMONTHYEARENS 500962014-05-07T06:00:0007 May 2014 06:00:00
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