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RBSP EFW PREAMPS. Rachel Hochman Space Sciences Laboratory University of California, Berkeley. Section Overview. Details of Changes since CDR Testing done, test flow Qualification -TVAC. Procedures written, Test reports written. Paperwork status Future Work. Instrument Block Diagram.
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RBSP EFW PREAMPS Rachel Hochman Space Sciences Laboratory University of California, Berkeley
Section Overview • Details of Changes since CDR • Testing done, test flow • Qualification -TVAC. • Procedures written, Test reports written. • Paperwork status • Future Work
Preamp Environmental Testing As discussed at CDR, the preamps must be qualified at a wider temperature range than the boom units as a whole. Therefore, they are thermally qualified prior to being installed in the booms. The preamps are monitored during thermal testing to make sure current consumption and offset voltage remain nominal.
Detail of Changes to Schematic New R2 value C2 Removed Feedback cap added
Feedback Cap During TVAC Qualification, an oscillation at power-on at the cold limit was discovered. The oscillation problem (PFR-001) was extensively studied by Steve Monson at UMN and determined to be a problem with the OP-15 opamp itself. After extensive bench and thermal testing, a feedback capacitor of 220 pF was added to stabilize the preamp and reduce the oscillation amplitude (3 Vpp down to 30 mVpp). Implementation was straightforward; the 220pF capacitors were soldered directly next to the feedback resistor on the flight preamps as requested in RBSP_EFW_PRE_ECN-ECO_Implementation_fbcap.doc (see photo below)
Gain Comparison Gain vs Frequency for the SPB preamp Frequency (kHz) Red curve is with 220 pF feedback capacitor Blue curve is without 220 pF feedback capacitor 5000 pF load to represent cable in both cases
Other PFRs PFR 12: On 5/28/10, during the pre-coating Mandatory Inspection Point (MIP), RBSP Project SMA discovered on SPB F1 units SN 16, 44, and 67, small nicks on front shield pads, exposing copper at pad. Further, SPB F1 units SN 06, 16, and 44 very small areas of coat peeling are present. PFR 13: During the pre-coating MIP, a partial non-wetting was discovered at a solder joint at C4 on AXB Preamp SN 01. These PFRs were resolved with Rework Forms RBSP_EFW_SPB_PRE_REWORK_PFR12.pdf andRBSP_EFW_SPB_PRE_REWORK_PFR13.pdf, respectively.
SPB F1 TEST FLOW Bench Test Fabrication PFR 01 (Oscillation at Cold) Rework MandatoryInspectionPoint (MIP) ConformalCoating ThermalVacuumTesting Cleaning MIP PFR 012 (Con-Coat and Pad Rework) Rework MIP Into Boom Unit Final Bench Test
AXB F1 TEST FLOW Fabrication Bench Test PFR 01 Rework Bench Test Cleaning MandatoryInspectionPoint (MIP) Thermal Vacuum Test MIP ConformalCoating PFR 013 Rework MIP Into Boom Final Bench Test
SPB F2, AXB F2 TEST FLOW Fabrication Bench Test Thermal Vacuum Test Cleaning MandatoryInspectionPoint (MIP) ConformalCoating MIP Into Boom Unit Final Bench Test
Spare Unit Test Flow Bench Spares 2 units each Fabrication Bench Test Thermal Vacuum Test Cleaning MandatoryInspectionPoint (MIP) ConformalCoating MIP Into Boom Unit Final Bench Test
Assembly and Test Procedures RBSP_EFW_PRE_005E_AXB_PWBAI RBSP_EFW_PRE_006E_SPB_PWBAI RBSP_EFW_PRE_007B_AXB_BenchTestProc RBSP_EFW_PRE_008B_SPB_BenchTestProc RBSP_EFW_PRE_009B_AXB_TVACProc RBSP_EFW_PRE_010A_SPB_TVACProc RBSP_EFW_PRE_011B_AXB_CoatingProc RBSP_EFW_PRE_012C_SPB_CoatingProcAll digitally signed and released.
Test Reports Written Bench test report TVAC reports Reviewed and signed by SysEng and QA; posted to Repository.
TVAC data Still need some work on graphs below Solid lines, no gray background, take home message at bottom. Distinguish between going cold and going hot (45 degree line vs vertical line in vout v temp)
SPB F2 Thermal Vacuum Data *One thermal cycle of SPB F2 testing
Traveler Status Travelers are complete (based on UCB SSL QA Review) and have passed inspection by RBSP Project SMA.
Future Work There is no work left to do on the individual preamp units. They are or are ready to be installed in the boom units.
PFR-001 Configuration: The preamps are in the Snout2 vacuum chamber, clamped to the cold plate. Harnessing comes out of chamber through the flanges and is attached to the preamp sampling board to which power is applied and from which data can be taken by the Keithley. A block diagram is attached. Test Plan: The plan was to put the preamps through one non-operative cycle: a 3 hour hot soak (105C) and a 3 hour cold soak (-160C) and then 7 operative cycles. They were to be off during the non-op cycle and powered on during the op cycles. The only exceptions to this were two planned power cycle tests, one at the hot extreme and one at the cold extreme. Problem: The anomaly occurred during the power cycle test at cold on the first operative cycle, when the preamps were found to draw more current than expected when powered back on. They were turned on at hot, and had been consuming the nominal amount of current until this point. The power supply was set with a current limit of 20mA per supply, because each preamp is expected to draw <4mA. Each unit was tested individually by disconnecting the other three external harnesses, and the current draw as read on the power supply was 8mA per supply. This is double what was expected, and this is true for all four units under test. The increased current draw was consistent, although occasional drops to nominal were seen. Note- this only occurs when powering on at cold. If the preamps are already on when the temperature drops, the current draw is nominal down to -160C. And a power cycle test at the hot extreme was successful.
PFR-007 The temperature was set for -160C, but the flow of LN2 seems to have been unregulated as the temperature reached -183C on the cold plate. As soon as this was spotted, the LN2 valve was closed and the heaters switched on to bring the plate back up to -160C. In total, the plate was colder than -160C for 30 minutes. The preamps were powered on the whole time, and as this was on the transition to cold, it is thought that the preamp boards themselves did not go out of the temperature limit. Additionally, throughout the half hour when the plate was below -160C, all four preamps maintained nominal current consumption and output voltage. The solenoid works best when upright, but was tilted as a result of being nudged while the nitrogen dewar was replaced, thus causing the solenoid to freeze. Once frozen, the solenoid was unable to restrict the flow of LN2 into the cold finger, and consequently the cold plate was cooled below the -160C limit. Although short, the amount of time the plate spent below -160C could have been even less had there been someone in the room continuously. A new support for the solenoid is being constructed, so that it remains completely upright at all times. Additionally, when thermal vacuum testing is in progress, the chamber will be manned continuously to make sure the temperature is stable. No negative consequences for the preamps themselves were observed- the current consumption on output voltage have been monitored since and the values have been nominal. They will be functionally tested after coating, to ensure no damage was done. Note: Testing done at the University of Minnesota brought the flight like ETU preamps down to -187C, and even after dwelling there for some time, the units continued to function properly. Therefore, we know that the opamp can survive such a low temperature
PFR-010 The computer that was being used to log the data from the preamp thermal vacuum tests froze over the weekend and upon returning on Monday morning, was unresponsive to the usual wakeup efforts. The computer was then restarted, however, the excel spreadsheet containing the information was not recovered. Data from 7 cycles on F1 and 6 cycles on F2 was lost. Many things contributed to this loss- the user’s failure to continuously save data, lack of auto-recover in the excelinx program, and a computer unsupported by sysadmin. For future tests, make sure the computer that holds data on flight boards is supported by sysadmin so that data can be recovered. Also, the user must be more conscious of saving data- perhaps there should be a step at certain points in the procedure informing the user to press the save button. As for having data on the preamp boards- the data from the final cycle of F2 is recorded and saved, and because both SPB preamp flight modules come from the same lot of preamp boards, data for one should be sufficient for both. The thermal cycles are meant solely to prove survival of the boards- none of the information gathered (ie current consumption and output voltage) are used for calibration. Therefore, retesting should not be necessary.
PFR-012 Configuration: The EFW Preamps, SN 06, 16, 44, and 67 were verified as clean and ready for coating. On 5/28/10, during the pre-coating Mandatory Inspection Point (MIP) inspection, William Whitehead, JHU/APL QA, discovered on units SN16, 44, 67, small nicks on pads, exposing copper at pad. Per NASA 8739.3, exposed copper that is not conformal coated or staked in not acceptable. Further, units SN6, 16, 44 very small areas of coat pealing are present. Per NASA 8739.1A, coat peeling is not acceptable. The technician who performed the work is trained to NASA 8739.3 and NASA 8739.1A and certified by UCB SSL QA. Coating needed to be manually removed from some pads, because the masking area was not marked on the drawing. The procedure RBSP_EFW_PRE_SPB_012_RevA did not show all areas that needed to be masked. The procedure was revised to RBSP_EFW_PRE_SPB_012_RevB. It now illustrates the entire area that needs to be masked. All additional units to be fabricated will be fabricated in accordance to the new revision. After rework, pictures of SN 06, 16, 44, and 67 were sent to JHU/APL QA. APL concurred with the rework and the inspections. The units passed MIP inspection and are ready for further processing. William Whitehead, JHU/APL QA, will send a copy of the revised APL supplier product verification audit report for the units, to reflect the material acceptance. After rework is complete, production for SN 06, 16, 44, and 67 shall continue on page 3, section 9, RBSP_EFW_PRE_SPB_012_RevB.
PFR-013 Configuration: The EFW AXB Preamp, SN 1was verified as clean and was ready for coating. On 5/28/10, during the Pre-coating MIP inspection, William Whitehead, JHU/APL QA, discovered a partial non-wetting at a solder joint (at C4 of the unit). Therefore, the unit failed inspection. The technician who performed the work is trained to surface mount and hand soldering (NASA 8739.2 and NASA 8739.3) and certified by UCB SSL QA. UCB SSL QA inspected the unit, SN 1. The small non-wetting area in the middle of the solder joint was not discovered during the initial inspection. An inspection of the board under a microscope at approximately 20X – 30X, at the time of the MIP revealed the non-wetting area at C4. Several days later, the unit was reworked (solder pad was re-soldered, spot cleaned) and re-inspected by UCB SSL Project QA. After rework, pictures of the solder joint were sent to JHU/APL QA. APL concurred with the rework and the inspections. The unit SN 1 passed MIP inspection and is ready for further processing. William Whitehead, JHU/APL QA, will send a copy of the revised APL supplier product verification audit report for SN 1, to reflect the material acceptance. AXB unit SN 1was e-tested by Rachel Hochman and passed 6/23/10
