Since I was focusing on the hot plate code and therefore did not need my weights, I decided to leave them on top of my samples for roughly 2 weeks.
It appears that an increased amount of time under pressure does not result in any noticable differences. A slight increase in surface area (SA) in two places, and a slight decrease in SA in another place, but overall no change. Note that "(initally)" in the picture below refers to http://nodus.ligo.caltech.edu:8081/Mariner/89.
Now that I have (relatively) good PWM code, I wanted to do my first real test with actual samples. Since everything went smoothly, I will now work on building the original set up for the project, which included attaching thermocouples to two plates so we could precisely measure the heat between them.
As you can see in the pictures below, I am running an Arduino off of my laptop which controls an AC/DC control replay that turns the AC power to the hot plate on and off.
Firstly, last night's heating did not change the contacted surface area greatly, but there is too many factors to speculate as to why that is the case. I leave that for future testing.
I attached the thermocouples by adhering them to the two aluminum plates. I was careful to make sure that the thermocouple was in the dead center of the aluminum plate. The other end of the thermocouples—exposed positive and negative wires—were screwed into the K Type connector so they can be plugged into the thermometer/multimeter. Taking the average between the top and bottom plate will give a more precise estimate of the temperature of the samples.
I intended to test the new thermocouple set up today, but when I plugged them in, both did not read a temperature. It took me a long time to figure out what went wrong: when installing the K Type thermocouple connector, the wires of the thermocouple need to be pushed in as far in as possible, otherwise the circuit would not be completed. It took a lot of trial and error to figure this out. I first created a test "circuit" with wire and a resistor to make sure that the connector itself was not broken. Then I carefully observed how moving the wires in different places affected the reading.
Once I did carefully reassemble the thermocouples, they worked perfectly, as indicated by the non-zero current. I ran tests with my three thermocouples and two devices to see how precise the temperature reading is. The results are below and pictures of the readings can be found in the zip file. I cannot explain why one of the adhered thermocouples is hotter than the other.
Plate #1 and 2 refers to the two different aluminum plates. T1 and T2 refers to the two ports on the Digital Thermometer 343. It cannot read two thermocouples simultaneously (as far as I can tell); it's so one can be used as a baseline/reference value for the other.
Since the two devices are giving different temperature readings, I would like to find out if this imprecision is linear (e.g. they are always 3°C off, so I just need to add/subtract 3°C after taking the measurements). If not, some sort of calibration is probably required. I decided to figure this out by running the heating tests I did before, but this time with the plates. This also serves as a test to see how the plates heat up.
Or rather, this is what I would have done, had I not realized that the thermometers were going down as the heat was increaing, meaning I had switched the polarity for both thermocouples. It turns out that this mix-up is a common mistake. I thought that I double checked that red was positive for thermocouples, but it is in fact not:
"red is the usual color for positive charges, whereas the red wire in thermocouple cables typically contains the negative signal. This coloration is ANSI standard for thermocouples, but it is not what most people expect."
I performed the same tests I have been doing prior (+180°C in 10 minutes) but now with the (correctly wired) thermocouples attached to the metal plates. The top plate is thermocouple #1 attached to the Fluke and the bottom plate is thermocouple #2 attached to the TPI (the lime green one).
The base heating rate for the new set up will require some tweaking to the code because the plates heat up much slower, but as I have mentioned previously, I do not think this will require a lot of extra work since I now know the tips and tricks to PWMing the hot plate. The only difficulty might come from the increase in hysteresis (i.e. the plates continue to increase in the temperature long after it turns off). For future tests, I need to remember to continue recording the temperature after program finishes its 10 min cycle.
On the positive, I think this test shows that taking the average of the two thermocouples to find the temperature in the center (where the optically contacted samples are) is a worthwhile endevor, considering how much the top plate lags behind the bottom plate in terms of heating speed.
With v3.0, I took a couple steps backwards by getting rid of the feature that increases the heating rate so I can isolate the base heating rate for the two plates. In my experience, the best way to figure out how to modify the program is to try a bunch of different target temperatures and heating times and look for correlations. I started with (attempting) to increase the plates by 280°C in 10 minutes.
For a future release, I am thinking of radically (relatively speaking) changing the function parameters: the user only inputs the target heating rate and how long the plates should be heated at this rate. This is to address the hysteresis in this new set-up, which I will elaborate on if I make the change.
I decided test how fast the plates would heat up if the heat was just on constantly on for 5 minutes. In general, these tests are raising a lot of questions in regards to controlling the temperature given the hysteresis in the system. It is also apparent that the bottom plate heats up signficantly faster than the top one, which means I need to heat the samples much longer than, say 10 minutes, if I want to avoid unevenly heating both parts of the optically contacted piece.
I also have to be conscientious that I am already half way through the quarter and ideally should be devoting time to bond strength testing rather than continuing to fiddle with the hot plate.
To combat the bottom plate heating up much faster than the top plate, I decided to try increasing the cycle period from 1000ms (1s) to 10000ms (10s). In other words, taking the test I today ran as an example, the hot plate will now be on for 1000ms then off for 9000ms then repeat. Hopefully this should give more time for the heat to transfer to the top plate, but even in this short test, it still appears to be a problem.
Due to the slower heating times, this will be a bit more challenging to test as each test could take hours to complete, but this is more in line with the final intended use anyways. Perhaps my cycle of 1000ms on is too much (e.g. I should do 100ms on then 9900ms off, although I think that might be so slow that it will never heat up; this also raising the question as to how I will deal with mantaining this slow heat up at the higher temperatures).
[I'm behind on data processing, but I'm creating an entry on the day I actually run the tests]
[I'm (once again) behind on data processing, but I'm creating an entry on the day I actually run the tests]
Somehow I never thought of this before, but instead of increasing the "on" time of the hot plate to account for the heating drop-off, I should keep that constant and instead decrease the "off" time. That feels more logical given that I am trying to keep the temperature of the two plates as close as possible.
The Arduino / AC PWM interface looks good. I recommend that you maintain the code in GitHub and post a link to the repo whenever you update the code. Use detailed commit messages so that it makes sense.
For the plotting, it would be good if you can use grid lines and markers for the data points. Then we can see the difference between the data and the fits, etc.
And to avoid the hysteresis, etc. you can record the temperature in your Arduino and use feedback to make the heater just go to whatever temperature you specify. So you would have a prescribed T(t) and the PID feedback loop would just make the heater take you there. Can your Arduino read the thermocouple?
The bond quality measurements can be split into two categories: destructive and nondestructive. For destructive, we have measuring tensile and shear strength, and for nondestructive, we have gap distrance and mechanical quality. I am also currently searching for more ways to measure the strenght, but I am having a hard time finding any others.
Proposed method: based off of the traditional razor test, a blade will be systematically inserted into the gap. For a prototype, I used optical bread board components to hold the razor while a knob was slowly turned to push the razor forward. The knob had markings on it, which could be used to estimate the amount of force applied to the gap. The prototype was made for the larger glass slides, so it is too big and forceful for the silicon and smaller, more fragile glass slides. However, the principles of the protoype had potential to be adapated to be gentler.
Proposed method: a cord will be adhered to the outer sides of the sample such that one side will be hung to the ceiling while the other will have weight hanging from it. Weight us added to the latter cord until the bond breaks. This could pontentially be a little dangerous as it could shatter when the bond finally breaks, so a protective barrier of some sort will have to be set up.
Alternative: affix one outer surface to the table so that it cannot move. Attach the other surface to something that can spun/twisted. The more twists it takes to break the bond corresponds to the shear strenght.
Proposed method: use ellipsometry to find how big the gap is between the two bonded surfaces. I think this would be great to combine with one of the destructive methods since, if you could relate the nm thickness of the gap to, say, the tensile strength, then you could estimate the tensile strength of future bonds without having to destroy them. I read a lot about ellipsometry over winter break, and I know what components are needed for it.
Proposed method: this would be based around the paper which measured the ring down of an optically contacted tuning fork. My focus would be on varying the parameters to find the most precise and accurate dimensions of the fork. Although it sounds interesting, I am not sure how practical it would be to pursue as it requires a lot of modeling and building. However, given the application of these measurements (specifically, for Voyager, (if my understanding is correct) the use of optical contacting will resolve the issue of messy noise caused by unpredictable thermal vibration of adhesives), knowing the mechanical quality of the bond seems valuble.
I am getting started on building the arduino circuit as well as setting up my computer so I can communicate between jupyter notebook and the arduino. I will need a USB adapter for my computer before I can make much more progress.
I was able to get a USB adapter for my computer so I could test my code. The Arduino can read the temperature of the room and output the values with a tenth of a second time delay. Jupyter Notebook recognizes the Arduino and can receive temperature data from it.
1) Paco cleared the path in the DOPO lab. We'll need a flat dolly or wooden bars (covered with a mylar sheet) to place the lid on it while we will remove the suspension. The suspension will be placed next to the wall and wrapped with mylar sheets.
(from the 40m) a dooly, mylar sheets, spare slings
(from Downs) heavy-duty inline scale
(from OMC lab) some tapes
2) The crane base is in CAML right now.
3) The yellow crane is in QIL right now. We'll dismount the top part and mount it on the base.
- Remove the lid. Place it on a clean safe platform.
- Remove the suspension, wrap it, and place it next the wall.
- Put the lid on.
- The chamber will be moved to CAML on Thu morning.
[JC, Stephen, Paco, Gabriele, Aidan, Radhika, Koji]
We have successfully extracted the crackle suspension from the chamber at the DOPO lab. We ended up using the engine hoist brought from the cryo lab instead of the yellow Skyhook as Skyhook's arm was too short.
Attachment 1 shows how the hoist is inserted to the table and how the lid was lifted. The lid was placed on a cardboard box wrapped with a Mylar sheet. It could be slid on the floor.
Attachment 2 shows how the suspension was lifted and placed on a similar Mylar-wrapped cardboard box. Upon the removal of the suspension, the cables were disconnected from the suspension. A few OSEM wires needed to be cut so that the suspension to be free.
Attachment 3 We are ready for the chamber transportation.
See the attachments.
Caltech transport came in this morning. They first went to the OMC lab and moved the 3ft x 4ft table out. They lifted the heavy objects only with human power.
Then the suspension chamber was moved with a hydraulic lifter. (Attachment 1)
The chamber bottom was sled on the table. We asked them to leave the chamber lid on the mylar + cardboard sheet (Attachment 2) so that we can carefully close the lid with a crane (Attachment 3).
JC and I continued to work on the chamber closure, but it wasn't so straightforward.
The nominally planned location of the table (seen in Attachment 3) has a low ceiling and was not a great place to open/close the lid. It is high enough just to close the lid but we can't do anything else.
We worked on the crane operation close to the lab entrance (Attachment 4). We found that the chamber needed to be offset from the center of the table because the legs of the hoist turned out to be too wide to get in between the table legs. This low ceiling had ~3" gap to the crane when the lid was closed (Attachment 5). Meaning, we can't put anything in the chamber if the lid gets stuck with the low ceiling.
Anyway, the chamber was closed and the table was rolled to the end of the lab (for storage) (Attachment 6).
BTW, the rolling of the table further destroyed the floor (Attachment 7)
So, how high the ceiling should be, so that we can put a tall suspension in the chamber? We probably need to use the northeast part of the lab where the ceiling is much higher. But the crane itself can be another limitation. It needs careful consideration.
I made a quick investigation of the crane configuration for the suspension test chamber.
CAML has three types of ceilings.
1) Low ceiling area (west side) the clearance height 75.5"
2) Mid ceiling area (most of the lab area) 85.5". This is limited by the height of the FL light cover.
3) High ceiling area (northeast corner) 105". This is limited by the height of the FL light cover there.
Nominal closed state: The chamber top height is about 68". Even in the low ceiling area, there is 7.5" space and the crane can remove the lid when the chamber is empty.
Open chamber with suspension (direct connection): If the lid and the hook are directly connected, the corner of the chamber is going to be very close to the jib arm when the chamber is fully opened with ~1" clearance. This is not a safe condition, considering that the chamber can oscillate due to the lateral motion associated with raising the jib arm.
Open chamber with suspension (connection via a 3" shackle): When the lid and the hook are connected via a 3" shackle, we'll observe a safe amount of clearance between the chamber and the jib arm. And the crane height is still 96" which is lower than the ceiling height of the high ceiling area of the lab.
The arduino was able to read temperature data and send it to a python program that graphed the data.
Upper limits on the mechanical loss of silicate bonds in a silicon tuning fork oscillatorâ€‹ and
Temperature Dependence of Losses in Mechanical Resonator Fabricated via the Direct Bonding of Silicon Strips
https://link.springer.com/article/10.1134/S1063782620010200 (I don't have access, but I was given a PDF of this paper over the summer)