The vacuum safety policy and design are not clear to me, and I don't know what the first and second defense is. Since we had limited time and bandwidth during the remotely-supported recovery work today, we wanted to work step by step.
The pressure rising rate is 20mtorr/day, and turning on TP3 early next week will resume the main-volume pumping without too much hustle. If you need the IFO time now, contact with Jon and use backing with TP3.
Didn't mean to sound whiny. I will wait until the vacuum team tells me it is okay.
[Jon, Jordan, Koji]
Today Jordan reconfigured the vac system to allow pumping of the main volume resume, with Jon and Koji remotely advising. All clear to resume normal IFO activities. However, the vac system is operating in a temporary configuration that will have to be reverted as we locate replacement components. Details below.
Since serial readback of the TP2 controller seems to be failing, we reconfigured the system with TP3 now backing for TP1. TP2 was valved off (at V4) and shut down until we can replace its controller.
TP3 has its own problems, however. It was valved off in January after its temperature readback began glitching and spuriously triggering the interlocks [ELOG 15140]. However the problem appears to be limited only one readback (rotation speed, current, voltage are fine) and there is enough redundancy in the pump-dependent interlock conditions to safely connect it to the main volume.
We also discovered that sometime since January, the TP3 dry pump has failed. The foreline pressure had risen to 165 torr. Since the TP2 and TP3 dry pumps are not interchangeable (Agilent vs. Varian), we instead valved in the auxiliary dry pump and disconnected the failed dry pump using a KF blank. This is a temporary arrangement until the permanent dry pump can be repaired. Jordan removed it to replace the tip seals and will test it in the bake lab before reinstalling.
With this configuration in place, we proceeded to pump down the main volume without issue (attachment 1). We monitored the pumpdown for about 45 min., until the pressure had reached ~1E-5 torr and TP3 had been transitioned to standby (low-speed) mode.
I missed the vacuum discussion on the call today, but I have some questions/comments:
At the very least, I think we should consider making the interlock code have levels (like interrupts on a micro controller). So if the pressure gauges are communicating and are reporting acceptable pressure readings, we should be able to reject unphysical readbacks from the TP controllers.
I still don’t understand why TP2 can’t back TP1, but we just disable all the software interlock conditions contingent on TP2 readbacks. This pump is far newer than TP3, and unless I’ve misunderstood something major about the vacuum infrastructure, I don’t really see why we should trust this flaky serial readbacks for any actionable interlocks, at least without some AND logic (since temperature, current and speed aren’t really independent variables).
I also think we should finally implement the email alert in the event the vacuum interlock is tripped. I can implement this if no one else volunteers.
This might also be a good reminder to get the documentation in order about the new vacuum system.
Looking at images of the old vac screens, the TP2/3 rotation speed and status string were digitally monitored. However I don't know if there were software interlocks predicated on those.
The temperature and current interlocks are implemented precisely because the pumps can shut themselves off. The concern is not about damaging the pumps (their internal logic protects against that); it's that a pump could automatically shut down and back-vent the IFO to atmosphere. Another interlock (e.g., the pressure differentials) might catch it, but it would depend on the back-vent rate and the scenario has never been tested. The temperature and current interlocks are set to trip just before the pump reaches its internal shut-down threshold.
One way we might be able to reduce our reliance on the flaky serial readbacks is to implement rotation-speed hardware interlocks. The old vac documentation alludes to these, but as far as Chub and I could determine in 2018, they never actually existed. The older turbo controllers, at least, had an analog output proportional to speed which could be used to control a relay to interrupt the V4/5 control signals. I'll look into this for the new controllers. If it could be done, we could likely eliminate the layer of serial-readback interlocks altogether.
That would be awesome if you're willing to volunteer. I agree this would be great to have.
I agree there were MEDM fields, but I can't find any record of these channels being recorded till 2018 December, so I don't agree that they were being digitally monitored. You can also look back in the elog (e.g. here and here) and see that the display fields are just blank. I would then assume that no interlocks were dependent on these channels, because otherwise the vacuum interlocks would be perpetually tripped.
Sorry but I'm having trouble imagining a scenario how the pressure gauges wouldn't register this before the IFO volume is compromised. Is there some back of the envelope calculations I can do to understand this? Since both the pressure gauges and the TP diagnostic channels are being monitored via EPICS, the refresh rate is similar, so I don't see how we can have a pump temperature / speed / current threshold tripped but NOT have this be registered on all the pressure gauges, seems like a bit of a contrived scenario to me. Our thresholds currently seem to be arbitrary numbers anyway, or are they based on some expected backstreaming rate? Isn't this scenario degenerate with a leak elsewhere in the vacuum envelope that would be caught by the differential pressure interlocks?
For the email alert, can you expose a soft channel that is a flag - if this flag is not 1, then the service will send out an email.
Right, I doubt they were ever recorded or used for interlocks. But the readbacks did work at one point in the past. There's a photo of the old vac monitor screen on p. 19 of E1500239 (last updated 2017) which shows the fields once alive.
I don't disagree that the pressure gauges would register the change. What I'm not sure about is whether the change would violate any of the existing interlock conditions, triggering a shutdown. Looking at what we have now, the only non-pump-related conditions I see that might catch it are the diffpres conditions:
abs(P2 - PTP2) > 1 torr (for a TP2 failure)
abs(P3 - PTP3) > 1 torr (for a TP3 failure)
abs(P1a - P2) > 1 torr (for either a TP2 or TP3 failure)
For the P1a-P2 differential, the threshold of 1 torr is the smallest value that in practice still allows us to pump down the IFO without having to disable the interlocks (P1a-P2 is the TP1 intake/exhaust differential). The purpose of the P2-PTP2/P3-PTP3 differentials is to prevent V4/5 from opening and suddenly exposing the spinning turbo to high pressure. I'm not aware of a real damage threshold calculation that any one has done; I think < 1 torr is lore passed down by Steve.
If a turbo pump fails, the rate it would backstream is unknown (to me, at least) and likely depends on the failure mode. The scenario I'm concerned about is if the backstream rate is slower than the conduction time through the pumspool and into the main volume. In that case, the pressure gauges will rise more or less together all the way up to atmosphere, likely never crossing the 1 torr differential pressure thresholds.
There's already a channel C1:Vac-error_status, where if the value is anything other than an empty string, there is an interlock tripped. Does that work?
I removed the backing pumps for TP2 and TP3 today to test ultimate pressure and determine if they need a tip seal replacement. This was done with Jon backing me on Zoom. We closed off TP3 and powered down TP3 and the auxilliary pump, in order to remove the forepumps from the exhaust line.
Once pumps were removed I connected a Pirani gauge to the pump directly and pumped down, results as follows:
TP2 Forepump (Agilent IDP 7):
TP3 Forepump (Varian SH 110):
TP3 forepump defintely needs a new tip seal, and while the pressure on TP2 Forepump was good there was a significant amount of particulate that came out of the exhaust line, so a new tip seal might not be needed but it is recommeded.
So why not just have a special mode for the interlock code during pumpdown and venting, and during normal operation we expect the main volume pressure to be <100uTorr so the interlock trips if this condition is violated? These can just be EPICS buttons on the Vac control MEDM screen. Both of these procedures are not "business as usual", and even if we script them in the future, it's likely to have some operator supervising, so I don't think it's unreasonable to have to switch between these modes. I just think the pressure gauges have demonstrated themselves to be much more reliable than these TP serial readbacks (as you say, they worked once upon a time, but that is already evidence of its flakiness?). The Pirani gauges are not ultra-reliable, they have failed in the past, but at least less frequently than this serial comm glitching. In fact, if these readbacks are so flaky, it's not impossible that they don't signal a TP shutdown? I just think the real power of having these multi-channel diagnostics is lost without some AND logic - a turbopump failure is likely to result in an increase in pump current and temperature increase and pump speed decrease, so it's not the individual channel values that should be determining if an interlock is tripped.
I definitely think that protecting the vacuum envelope is a priority - but I don't think it should be at the expense of commissioning time. But if you think these extra interlocks are essential to the safety of the vacuum system, I withdraw my request.
It would be better to have a flag channel, might be useful for the summary pages too. I will make it if it is too much trouble.
I agree with your assessment, Jordan. If I'm not mistaken the scroll pump for TP2 is new; we had a very early failure with the last new scroll pump (the forepump for TP3) tip seals at just over 5000 hours. Glad to see my replacement seals held up for over 60K hours. If this is the trend with these pumps, we can simply run them to around 60000 hours and replace the seals at that time, rather than waiting for failure! - Chub
I've created a purchase list of hardware needed to restore the aging vacuum system. This wasn't planned as part of the BHD upgrade, but I've added it to the BHD procurement list since hardware replacements have become necessary.
The list proposes replacing the aging TP3 Varian turbo pump with the newer Agilent model which has already replaced TP2. It seems I was mistaken in believing we already had a second Agilent pump on hand. A thorough search of the lab has not turned it up, and Steve himself has told me he doesn't remember ordering a second one. Fortunately Steve did leave us a detailed Agilent parts list [ELOG 14322].
It also proposes replacing the glitching TP2 Agilent controller with a new one. The existing one can be sent back for repair and then retained as a spare. Considering that one of these controllers is already malfunctioning after < 2 years, I think it's a very good idea to have a spare on hand.
Below is our current list of vacuum hardware issues. Items that this purchase list will address (limited to only the most urgent) are highlighted in yellow.
I think we should discuss interlock possibilities at a 40m meeting. I'm reluctant to make the system more complicated, but perhaps we can find ways to reduce the reliance on the turbo pump readbacks. I agree they've proven to be the least reliable.
While we may be able to improve the tolerance to certain kinds of hardware malfunctions (and if so, we should), I don't see interlocks triggering on abnormal behavior of critical equipment as the root problem. As I see it, our bigger problem is with all the malfunctioning, mostly end-of-lifetime pieces of vacuum equipment still in use. If we can address the hardware problems, as I'm trying to do with replacements [ELOG 15412], I think that in itself will make the interlocking much less of an issue.
Ok, this can be added pretty easily. Its value will just be toggled between 1 and 0 every time the interlock server raises/clears the existing string channel. Adding the channel will require restarting the whole vac IOC, so I'll do it at a time when Jordan is on hand in case something fails to come back up.
For this particular email service, ideally the email should be sent out as soon as the interlock is tripped, so this would require a line of code to be added to the main interlock code. Which I guess would require a restart of the interlock service. So let me know when you guys plan to do the dry-pump tip seal replacement operation (when I presume valves will be closed anyways) so that we can do this in a minimally invasive way.
Tip Seals were replaced on the forepumps for TP2 and TP3, and both are ready to be installed back onto the forelines.
TP2 Forepump Ultimate Pressure: 180 mtorr
TP3 Forepump Ultimate Pressure: 120 mtorr
The vac system is going down at 11 am today for planned maintenance:
We will advise when the work is completed.
This work is finally complete. The dry pump replacement was finished quickly but the controls updates required some substantial debugging.
For one, the mailer code I had been given to install would not run against Python 3.4 on c1vac, the version run by the vac controls since about a year ago. There were some missing dependencies that proved difficult to install (related to Debian Jessie becoming unsupported). I ultimately solved the problem by migrating the whole system to Python 3.5. Getting the Python keyring working within systemd (for email account authentication) also took some time.
Edit: The new interlock flag channel is named C1:Vac-interlock_flag.
Along the way, I discovered why the interlocks had been failing to auto-close the PSL shutter: The interlock was pointed to the channel C1:AUX-PSL_ShutterRqst. During the recent c1psl upgrade, we renamed this channel C1:PSL-PSL_ShutterRqst. This has been fixed.
The main volume is being pumped down, for now still in a TP3-backed configuration. As of 8:30 pm the pressure had fallen back to the upper 1E-6 range. The interlock protection is fully restored. Any time an interlock is triggered in the future, the system will send an immediate notification to 40m mailing list. 👍
I propose we go for all CAPS for all channel names. The lower case names is just a holdover from Steve/Alan from the 90's. All other systems are all CAPS.
It avoids us having to force them all to UPPER in the scripts and channel lists.
I looked into how the new UPS devices suggested by Chub would communicate with the vac interlocks. There are several possible ways, listed in order of preference:
I recommend we proceed with ordering the Tripp Lite 36HW20 for TP1 and Tripp Lite 1AYA6 for TP2 and TP3 (and other 120V electronics). As far as I can tell, the only difference between the two 120V options is that the 6FXN4 model is TAA-compliant.
Chub has placed the order for two new UPS units (115V for TP2/3 and a 220V version for TP1).
They will arrive within the next two weeks.
This year we've struggled with vacuum controls unreliability (e.g., spurious interlock triggers) caused by decaying hardware. Here are details of the vacuum refurbishment plan I described on the 40m call this week.
☑ Refurbish TP2 and TP3 dry pumps. Completed [ELOG 15417].
☑ Automated notifications of interlock-trigger events. Email to 40m list and a new interlock flag channel. Completed [ELOG 15424].
☐ Replace failing UPS.
☐ Remove interlock dependencies on TP2/TP3 serial readbacks. Due to persistent glitching [ELOG 15140, ELOG 15392].
Unlike TP2 and TP3, the TP1 readbacks are real analog signals routed to Acromags. As these have caused us no issues at all, the plan is to eliminate dependence on the TP2/3 digital readbacks in favor of the analog controller outputs. All the digital readback channels will continue to exist, but the interlock system will no longer depend on them. This will require adding 2 new sinking BI channels each for TP2 and TP3 (for a total of 4 new channels). We have 8 open Acromag XT1111 channels in the c1vac system [ELOG 14493], so the new channels can be accommodated. The below table summarizes the proposed changes.
I installed the Tripp Lite SMX1000RT2U and Tripp Lite Smart1000LCD at the bottom of the 1x8 electronics rack. These are plugged in to power, and are ready for testing. All other cables (serial, usb, etc.) have been left on the table next to the 1x8 rack.
To carry out the next steps of the vac refurbishment plan [ELOG 15499], I've ordered parts necessary for interfacing the UPS units and the analog TP2/3 controller outputs with c1vac. The purchase list is appended to the main BHD list and is located here. Some parts we already had in the boxes of Acromag materials. Jordan is gathering what we do already have and staging it on the vacuum controls console table - please don't move them or put them away.
This afternoon Jordan is going to carry out a test of the V4 and V5 hardware interlocks. To inform the interlock improvement plan , we need to characterize exactly how these work (they pre-date the 2018 upgrade). I have provided him a sequence of steps for each test and will also be backing him up on Zoom.
We will close V1 as a precaution but there should be no other impact to the IFO. The tests are expected to take <1 hour. We will advise when they are completed.
This test has been completed. The IFO configuration has been reverted to nominal.
For future reference: yes, both the V4 and V5 hardware interlocks were found to still be connected and work. A TTL signal from the analog output port of each pump controller (TP2 and TP3) is connected to an auxiliary relay inside the main valve relay box. These serve the purpose of interupting the (Acromag) control signal to the primary V4/5 relay. This interrupt is triggered by each pump's R1 setpoint signal, which is programmed to go low when the rotation speed falls below 80% of the low-speed setting.
The vac system is going down now for planned repairs [ELOG 15499]. It will likely take most of the day. Will advise when it's back up.
Vacuum work is completed. The TP2 and TP3 interlocks have been overhauled as proposed in ELOG 15499 and seem to be performing reliably. We're now back in the nominal system state, with TP2 again backing for TP1 and TP3 pumping the annuli. I'll post the full implementation details in the morning.
I did not get to setting up the new UPS units. That will have to be scheduled for another day.
Yesterday I completed the switchover of small turbo pump interlocks as proposed in ELOG 15499. This overhaul altogether eliminates the dependency on RS232 readbacks, which had become unreliable (glitchy) in both controllers. In their place, the V4(5) valve-close interlocks are now predicated on an analog controller output whose voltage goes high when the rotation speed is >= 80% of the nominal setpoint. The critical speed is 52.8 krpm for TP2 and 40 krpm for TP3. There already exist hardware interlocks of V4(5) using the same signals, which I have also tested.
Unlike the TP1 controller, which exposes simple relays whose open/closed states are sensed by Acromags, what the TP2(3) controllers output is an energized 24V signal for controlling such a relay (output circuit pictured below). I hadn't appreciated this difference and it cost me time yesterday. The ultimate solution was to route the signals through a set of new 24V Phoenix Contact relays installed inside the Acromag chassis. However, this required removing the chassis from the rack and bringing it to the electronics bench (rather than doing the work in situ, as I had planned). The relays are mounted to the second DIN rail opposite the Acromags. Each TP2(3) signal controls the state of a relay, which in turn is sensed using an Acromag XT1111.
The TP2(3) "normal-speed" signals are already in use by hardware interlocks of V4(5). Each signal is routed into the main AC relay box, where it controls an "interrupter" relay through which the Acromag control signal for the main V4(5) relay is passed. These signals are now shared with the digital controls system using a passive DB15 Y-splitter. The signal routing is shown below.
The new turbo-pump-related interlock conditions and their channel predicates are listed below. The full up-to-date channel list and wiring assignments for c1vac are maintained here.
There are two new channels, both of which provide a binary indication of whether the pump speed is outside its nominal range. I did not have enough 24V relays to also add the C1:Vac-TP2(3)_fail channels listed in ELOG 15499. However, these signals are redundant with the existing interlocks, and the existing serial "Status" readback will already print failure messages to the MEDM screens. All of the TP2(3) serial readback channels remain, which monitor voltage, current, operational status, and temperature. The pump on/off and low-speed mode on/off controls remain implemented with serial signals as well.
The new analog readbacks have been added to the MEDM controls screens, circled below:
I'm in the lab this morning to interface the two new UPS units with the digital controls system. Will be out by lunchtime. The disruptions to the vac system should be very brief this time.
I'm leaving the lab shortly. We're not ready to switch over the vac equipment to the new UPS units yet.
The 120V UPS is now running and interfaced to c1vac via a USB cable. The unofficial tripplite python package is able to detect and connect to the unit, but then read queries fail with "OS Error: No data received." The firmware has a different version number from what the developers say is known to be supported.
The 230V UPS is actually not correctly installed. For input power, it has a general type C14 connector which is currently plugged into a 120V power strip. However this unit has to be powered from a 230V outlet. We'll have to identify and buy the correct adapter cable.
With the 120V unit now connected, I can continue to work on interfacing it with python remotely. The next implementation I'm going to try is item #2 of this plan [ELOG 15446].
I found that the control MEDM screen was left open on the c1vac workstation. This should be closed every time you leave the workstation, to avoid accidental button pressing and such.
The network outage meant that the EPICS data from the pressure gauges wasn't recorded until I reset everything ~noon. So there isn't really a plot of the outgassing/leak rate. But the pressure rose to ~2e-4 torr, over ~4 hours. The pumpdown back to nominal pressure (9e-6 torr) took ~30 minutes.
The vac controls are going down now to pull and test software changes. Will advise when the work is completed.
The vac work is completed. All of the vacuum equipment is now running on the new 120V UPS, except for TP1. The 230V TP1 is still running off wall power, as it always has. After talking with Tripp Lite support today, I believe there is a problem with the 230V UPS. I will post a more detailed note in the morning.
Yesterday's UPS switchover was mostly a success. The new Tripp Lite 120V UPS is fully installed and is communicating with the slow controls system. The interlocks are configured to trigger a controlled shutdown upon an extended power outage (> ~30 s), and they have been tested. All of the 120V pumpspool equipment (the full c1vac/LAN/Acromag system, pressure gauges, valves, and the two small turbo pumps) has been moved to the new UPS. The only piece of equipment which is not 120V is TP1, which is intended to be powered by a separate 230V UPS. However that unit is still not working, and after more investigation and a call to Tripp Lite, I suspect it may be defective. A detailed account of the changes to the system follow below.
Unfortunately, I think I damaged the Hornet (the only working cathode ionization gauge in the main volume) by inadvertently unplugging it while switching over equipment to the new UPS. The electronics are run from multiple daisy-chained power strips in the bottom of the rack and it is difficult to trace where everything goes. After the switchover, the Hornet repeatedly failed to activate (either remotely or manually) with the error "HV fail." Its compatriot, the Pirani SuperBee, also failed about a year ago under similar circumstances (or at least its remote interface did, making it useless for digital monitoring and control). I think we should replace them both, ideally with ones with some built-in protection against power failures.
Four new soft channels per UPS have been created, although the interlocks are currently predicated on only C1:Vac-UPS120V_status.
These new readbacks are visible in the MEDM vacuum control/monitor screens, as circled in Attachment 1:
Yesterday I brought with me a custom power cable for the 230V UPS. It adapts from a 208/120V three-phase outlet (L21-20R) to a standard outlet receptacle (5-15P) which can mate with the UPS's C14 power cable. I installed the cable and confirmed that, at the UPS end, 208V AC was present split-phase (i.e., two hot wires separated 120 deg in phase, each at 120V relative to ground). This failed to power on the unit. Then Jordan showed up and suggested to try powering it instead from a single-phase 240V outlet (L6-20R). However we found that the voltage present at this outlet was exactly the same as what the adapter cable provides: 208V split-phase.
This UPS nominally requires 230V single-phase. I don't understand well enough how the line-noise-isolation electronics work internally, so I can think of three possible explanations:
I called Tripp Lite technical support. They thought the unit should work as powered in the configuration I described, so this leads me to suspect #3.
@Chub and Jordan: Can you please look into somehow replacing this unit, potentially with a U.S.-specific model? Let's stick with the Tripp Lite brand though, as I already have developed the code to interface those.
Unlike our older equipment, which communicates serially with the host via RS232/485, the new UPS units can be connected with a USB 3.0 cable. I found a great open-source package for communicating directly with the UPS from within Python, Network UPS Tools (NUT), which eliminates the dependency on Tripp Lite's proprietary GUI. The package is well documented, supports hundreds of power-management devices, and is available in the Debian package manager from Jessie (Debian 8) up. It consists of a large set of low-level, device-specific drivers which communicate with a "server" running as a systemd service. The NUT server can then be queried using a uniform set of programming commands across a huge number of devices.
I document the full set-up procedure below, as we may want to use this with more USB devices in the future.
First, install the NUT package and its Python binding:
$ sudo apt install nut python-nut
This automatically creates (and starts) a set of systemd processes which expectedly fail, since we have not yet set up the config. files defining our USB devices. Stop these services, delete their default definitions, and replace them with the modified definitions from the vacuum git repo:
$ sudo systemctl stop nut-*.service
$ sudo rm /lib/systemd/system/nut-*.service
$ sudo cp /opt/target/services/nut-*.service /etc/systemd/system
$ sudo systemctl daemon-reload
Next copy the NUT config. files from the vacuum git repo to the appropriate system location (this will overwrite the existing default ones). Note that the file ups.conf defines the UPS device(s) connected to the system, so for setups other than c1vac it will need to be edited accordingly.
$ sudo cp /opt/target/services/nut/* /etc/nut
Now we are ready to start the NUT server, and then enable it to automatically start after reboots:
$ sudo systemctl start nut-server.service
$ sudo systemctl enable nut-server.service
If it succeeds, the start command will return without printing any output to the terminal. We can test the server by querying all the available UPS parameters with
$ upsc 120v
which will print to the terminal screen something like
device.mfr: Tripp Lite
device.model: Tripp Lite UPS
driver.version.data: TrippLite HID 0.81
ups.mfr: Tripp Lite
ups.model: Tripp Lite UPS
Here 120v is the name assigned to the 120V UPS device in the ups.conf file, so it will vary for setups on other systems.
If all succeeds to this point, what we have set up so far is a set of command-line tools for querying (and possibly controlling) the UPS units. To access this functionality from within Python scripts, a set of official Python bindings are provided by the python-nut package. However, at the time of writing, these bindings only exist for Python 2.7. For Python 3 applications (like the vacuum system), I have created a Python 3 translation which is included in the vacuum git repo. Refer to the UPS readout script for an illustration of its usage.
Assembled is the list of dead pressure gauges. Their locations are also circled in Attachment 1.
For replacements, I recommend we consider the Agilent FRG-700 Pirani Inverted Magnetron Gauge. It uses dual sensing techniques to cover a broad pressure range from 3e-9 torr to atmosphere in a single unit. Although these are more expensive, I think we would net save money by not having to purchase two separate gauges (Pirani + hot/cold cathode) for each location. It would also simplify the digital controls and interlocking to have a streamlined set of pressure readbacks.
For controllers, there are two options with either serial RS232/485 or Ethernet outputs. We probably want the Agilent XGS-600, as it can handle all the gauges in our system (up to 12) in a single controller and no new software development is needed to interface it with the slow controls.
I came to the campus and Gautam notified that he just had received the alert from the vac watchdog.
I checked the vac status at c1vac. PTP3 went up to 10 torr-ish and this made the diff pressure for TP3 over 1torr. Then the watchdog kicked in.
To check the TP3 functionality, AUX RP was turned on and the manual valve (MV in the figure) was opened to pump the foreline of TP3. This easily made PTP3 <0.2 torr and TP3 happy (I didn't try to open V5 though).
So the conclusion is that RP for TP3 has failed. Presumably, the tip-seal needs to be replaced.
Right now TP3 was turned off and is ready for the tip-seal replacement. V5 was closed since the watchdog tripped.
Disconcerting because those tip seals were just replaced . Maybe they were just defective, but if there is a more serious problem with the pump, there is a spare Varian roughing pump (the old TP2 dry pump) sitting at the X-end.
I reset the interlock error to unfreeze the vac controls (leaving V5 closed).
I removed the forepump (Varian SH-110) for TP3 today to see why it had failed over the weekend. I tested it in the C&B lab and the ultimate pressure was only ~40torr. I checked the tip seals and they were destroyed. The scroll housing also easily pulled off of the motor drive shaft, which is indicative of bad bearings. The excess travel in the bearings likely led to significant increase in tip seal wear. This pump will need to be scrapped, or rebuilt.
I tested the spare Varian SH-110 pump located at the X-end and the ultimate pressure was ~98 mtorr. This pump had tip seals replaced on 11/5/18, and is currently at 55163 operating hours. It has been installed as the TP3 forepump.
Once installed, restarting the pump line occured as follows: V5 Closed, VA6 closed, VASE Closed, VASV closed, VABSSCI closed, VABS closed, VABSSCO closed, VAEV closed, VAEE closed,TP3 was restarted and once at normal operation, valves were opened in same order.
The pressure differential interlock condition for V5 was temporaily changed to 10 torr (by Gautam), so that valves could be opened in a controlled manner. Once, the vacuum system was back to normal state the V5 interlock condition was set back to the nominal 1 torr. Vacuum system is now running normally.
The interlocks tripped at ~630am local time. Jordan reported that TP2 was supposedly running at 52 C (!).
V1 was already closed, but TP2 was still running. With him standing by the rack, I remotely exectued the following sequence:
Jordan confirmed (by hand) that TP2 was indeed hot and this is not just some serial readback issue. I'll do the forensics later.
Here is the timeline. This suggests TP2 backing RP failure.
1st line: TP2 foreline pressure went up. Accordingly TP2 P, current, voltage, and temp went up. TP2 rotation went down.
2nd line: TP2 temp triggered the interlock. TP2 foreline pressure was still high (10torr) so TP2 struggled and was running at 1 torr.
3rd line: Gautam's operation. TP2 was isolated and stopped.
Between the 1st line and 2nd line, TP2 pressue (=TP1 foreline pressure) went up to 1torr. This made TP1 current increased from 0.55A to 0.68A (not shown in the plot), but TP1 rotation was not affected.
I removed the forepump to TP2 this morning after the vacuum failure, and tested in the C&B lab. I pumped down on a small volume 10 times, with no issue. The ultimate pressure was ~30 mtorr.
I re-installed the forepump in the afternoon, and restarted TP2, leaving V4 closed. This will run overnight to test, while TP3 backs TP1.
In order to open V1, with TP3 backing TP1, the interlock system had to be reset since it is expecting TP2 as a backing pump. TP2 is running normally, and pumping of the main volume has resumed.
Unclear why the TP2 foreline pump failed in the first place, it has been running fine for several hours now (although TP2 has no load, since V4 isolates it from the main volume). Koji's plots show that the TP2 foreline pressure did not recover even after the interlock tripped and V4 was closed (i.e. the same conditions as TP2 sees right now).
I have placed 3 new in box, IDP 7 forepumps along the x arm of the interferometer. These are to be used as spares for both the 40m and Clean and Bake.
I've uploaded some more photos here. I believe the problem is a worn out thread where the main rotary handle attaches to the shaft that operates the valve.
This morning, I changed the valve config such that TP2 backs TP1 and that combo continues to pump on the main volume through the partially open RV2. TP3 was reconfigured to pump the annuli - initially, I backed it with the AUX drypump but since the load has decreased now, I am turning the AUX drypump off. At some point, if we want to try it, we can try pumping the main volume via the RGA line using TP2/TP3 and see if that allows us to get to a lower pressure, but for now, I think this is a suitable configuration to continue the IFO work.
There was a suggestion at the meeting that the saturation of the main volume pressure at 1mtorr could be due to a leak - to test, I closed V1 for ~5 hours and saw the pressure increased by 1.5 mtorr, which is in line with our estimates from the past. So I think we can discount that possibility.
It is stored along with the cables that arrived a few weeks ago, awaiting the gauges which are now expected next week sometime.
Five Agilent pressure gauges were delivered to the 40m. It is stored with the controller and cables in the office area. This completes the inventory for the gauge replacement - we have all the ordered parts in hand (though. not necessarily all the adaptor flanges etc). I'll see if I can find some cabinet space in the VEA to store these, the clutter is getting out of hand again...
in addition, the spare gate valve from LHO was also delivered today to the 40m. It is stored at EX with the other spare valves.
Now that the new Agilent full-range gauges (FRGs) have been received, I'm putting together an installation plan. Since my last planning note in Sept. (ELOG 15577), two more gauges appear to be malfunctioning: CC2 and PAN. Those are taken into account, as well. Below are the proposed changes for all the sensors in the system.
The latest greatest UPS has been delivered. I will move it to near the vacuum rack in its packaging for storage. It weighs >100lbs so care will have to be taken when installing - can the rack even support this?
Update to the gauge replacement plan (15692), based on Jordan's walk-through today. He confirmed:
Based on this info (and also info from Gautam that the PAN gauge is still working), I've updated the plan as follows. In summary, I now propose we install the fifth FRG in the TP1 foreline (PTP1 location) and leave P2 and P3 where they are, as they are no longer needed elsewhere. Any comments on this plan? I plan to order all the necessary gaskets, blanks, etc. tomorrow.
Around 7pm, the UPS at the vacuum rack seems to have failed. Don't ask me why I decided to check the vacuum screen 10 mins after the failure happened, but the point is, this was a silent failure so the protocols need to be looked into.
Going to the rack, I saw (unsurprisingly) that the 120V UPS was off.
For now, I think this is a safe state to leave the system in. Unless I hear otherwise, I will leave it so - I will be in the lab another hour tonight (~10pm).
Some photos and a screen-cap of the Vac medm screen attached.
Is that a fault code that you can decipher in the manual, or just a light telling you nothing but your UPS is dead?
I can't find anything in the manual that describes the nature of the FAULT message. In fact, it's not mentioned at all. If the unit detects a fault at its output, I would expect a bit more information. This unit does a programmable level of input error protection, too, usually set at 100%. Still, there is no indication in the manual whether an input issue would be described as a fault; that usually means a short or lifted ground at the output.