The relays in the DEA are a type of switch which can be flipped by remote control. There are five of them, located on DEA board 11, each of which governs which DEA power supply operates two of the video board and CCD combinations. Each CCD is hardwired to one video board. Each pair of video boards and CCDs can be selected independently to be powered from either DEA side A or DEA side B's 28 volt supply.
The pairs are as follows:
SYSSET item chips powered
SYSSET_CNTL_RELAY_SET_1 I0 and S0
SYSSET_CNTL_RELAY_SET_2 I1 and S1
SYSSET_CNTL_RELAY_SET_3 I2 and S3
SYSSET_CNTL_RELAY_SET_4 I3 and S2
SYSSET_CNTL_RELAY_SET_5 S4 and S5
The relays are designed in such a way that they do not change setting if there is no power to the coils. Each one has two coils, one pulling it to the A side and one to the B side. (The actual hardware pushes the contact, but that's a detail. Logically, one can think of pulling.)
The power for pulling the relays to the A side comes from board 11, and is available for use when the DEA A is powered on. The power for pulling the relays to the B side comes from board 12, and is available for use when the DEA B is powered on.
Bob Goeke cautions us that we must never power up both sides of the DEA. This would complicate the troubleshooting of video board electrical issues. There is logic in the power supplies to turn off DEA side B in the event that both sides are commanded on at the same time.
In addition, DEA board 11 hosts a number of sensors that can be read out in DEA housekeeping data. This includes the item RELAY visible in the DEA housekeeping section of the PMON display. This item is also known as DEAHOUSE_CNTL_RELAY in the deaHousekeepingData packets. Five bits are used, one for each of the 5 relays. A bit value of 1 indicates the relay is pulled to the A side, that is, the pair of video boards and CCDs are set to be powered from DEA side A. The readings are accurate only when board 11 is powered (by DEA side A). When running on DEA side B, all the bits will be zero regardless of the relay status. (see the IPCL.)
Most of board 11 is powered from DEA side A. However, the side B power is jumpered via the backplane to board 11 relays, to allow for energizing the coils, and for powering video boards via these relays.
.... Peter and Bob have developed a draft flowchart and SOPs for use in troubleshooting power anomalies. As of 2017, the only power anomalies ACIS has experienced in flight are of the type where a power supply is commanded OFF by a single event upset. The remedy is simple: after verifying all was well until the major frame where the anomaly occurred, turn the power supply on again, and then perform cleanup actions depending on what was powered down. We have anomaly pages for these, linked from here: Anomaly Pages.
For more complex anomalies, please refer to the flowchart, here: DEA anomaly flowchart
In particular, Peter works through the process of swapping from DEA A to DEA B, including flipping the power relays one at a time, and verifying nothing untoward happens as each video board and CCD is powered up. This is done with the switch_deaa_b SOP for switching from side A to side B. [This SOP is due for further development by ACIS Ops.]
On Mon, Jul 24, 2017 at 4:54 PM cgrant wrote:
WSRELAY0_4 is an existing command that sets all five relays at once. It's equivalent to sending WS_RELAY_0, WS_RELAY_1, WS_RELAY_2, WS_RELAY_3, WS_RELAY_4, which are the commands used in the switch dea SOPs.
S/W user guide here, section 2.1, has a description of the hardware: S/W User Guide
These commands have the effect of "pulling" the relay so that those 2 boards are powered from the active DEA power supply, so the same command can pull the other way if the other DEA is powered up. Peter proposes building commands that poke a '2' into the relevant place in the BEP system configuration table, when switching relays to the B side. Any non-zero value will do, but the BEP needs to see a change in order to execute the command. This will also allow interpretation of the system config table dump.
Note that a cold boot of the BEP fills the sys config table to all zeroes, so any subsequent relay commands would pull the relays to whichever DEA is powered up at the time.
The WSPOW commands in step 8 of Peter's switch_deaa_b (and ...b_a) sequentially power up more and more video boards. Under some circumstances (e.g. looking for a board that may have a short or other anomaly), we may wish to skip one or more boards (e.g. suspected short circuit or other problem on one board). Perhaps we should power them up only one at a time, setting a single bit in the WSPOW0... commands. This would power down all the other boards.