DPU Overcurrent

 

Background:

 

The DPU overcurrent AP#21/RTS #34 protects against high current to the DPU.

 

If the DPU current is greater than 2.2 Amps for 7 seconds, then AP#21 will start RTS #34 which will turning off all mechanisms, the wax actuators, the instrument operational heaters, and the DPU power. Then RTS #34 will start RTS#33, which turns the decontamination heaters off.

 

Throughout I&T, this condition often occurred due to sequences exercising various mechanisms in combination with one another which created current spikes that were synchronized with the telemetry update rate. Although, we think 2.2 amps for 7 seconds will not ever occur, spikes of 2.2 amps have been seen and are to be expected.

Key Telemetry:

 

Event #1017 - Instrument DPU OverCurrent sensed (0011, 0022, 0007) - where

0018 is the number of the action point that failed (x11 = 17 decimal)

0022 is the number of the RTS that executed (x22 = 34 decimal)

0007 is the number of counts

 

Event #552 - Action Result changed from Pass to Fail (0011) - where again 0011 is the actionpoint that failed.

 

Also, the following will be ~0 amps and will shows OFF on the PSPWRDIS page.

DPU current (PSDPUCURR)

Motor Current (IIAEMTR)

Sequence ID that was executing when the event occurred (see timeline)

Instrument operational heater current

Wax actuator current

Decontamination heater current

 

Recovery Procedure:

 

Notify EOF and OE before taking corrective action.

 

  1. Actionpoint #17 should be set to active to reset the overcurrent protection

  2. Power up the instrument as prescribed in the Flight Procedures Document

 

 

References:

 

TRACE C&DH FSW User’s Guide

 

http://tracedata.nascom.nasa.gov/~trace/cdhsw/trace/design/sc/pre_rts.htm