Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_beauty_night_skies.thumb.jpg.2711ade15e31d01524e7dc52d15c4217.jpg

Gina

All Sky Camera Revisited

Recommended Posts

Been Googling about washing machine pressure switches and found they may have 2 or 3 separate sets of contacts operating at different pressures.  See THIS VIDEO.  The one I've ordered would appear to have two sets of change over contacts so two pressure switches in one.  The higher pressure one could flag a warning and the lower one danger, assuming the higher pressure isn't too high but I think that unlikely as water levels in the machine may be 6" to 8" I reckon.  Whilst just a small positive pressure would be sufficient I don't think a higher pressure would hurt.  If there is a leak the pressure would just drop faster but the whole ides is not to have a leak.  If I feed the switch wires to the RPi, the client app could show green light for good, orange for a warning and red for danger.

Share this post


Link to post
Share on other sites

Exactly. Its a bit of work to wire all that and more to adjust the setpoint and hysteresis for each of the two switches, but the result would be more informative.

My thought about having a volume at the control room end was to have enough dry air to feed the leak. But we have little idea of the magnitude of the leak that needs feeding. On the positive side, this method of dehumidification actually requires there to be a leak in the camera volume. Otherwise there would be no nett inflow of dried air, and no therapeutic effect, and some form of twin-tubed air exchange mechanism or controlled-leak would be required, with more complexity.

Share this post


Link to post
Share on other sites

Btw : High pressure in printed part is no problem at all. Care should be taken how the slicer is set, otherwise the part will crack.
Just made a water-rocket-launching-platform for my neighbours son. He took it with him on a camping trip last week and had lots of fun with it. I tested it until the printed part eventually cracked. That was when I got as high as 12-bar. That crucial printed part is the specially made conversion from Gardena-male to 1.5 litre Coke bottles.
We got as high as 35meter at 10bar btw, and at the same time were all soaking wet...
Next time I will make a 2-stage water-rocket, and we're aiming at 100meter...:laugh2:

  • Thanks 1

Share this post


Link to post
Share on other sites
16 minutes ago, tonyowens_uk said:

Exactly. Its a bit of work to wire all that and more to adjust the setpoint and hysteresis for each of the two switches, but the result would be more informative.

My thought about having a volume at the control room end was to have enough dry air to feed the leak. But we have little idea of the magnitude of the leak that needs feeding. On the positive side, this method of dehumidification actually requires there to be a leak in the camera volume. Otherwise there would be no nett inflow of dried air, and no therapeutic effect, and some form of twin-tubed air exchange mechanism or controlled-leak would be required, with more complexity.

The ASC enclosure will have desiccant (several 10g silica gel sachets) to dry the air and previous results show this works and there was no condensation at -20°C.  This tells me that nett inflow of dried air is not actually needed.  I'd be surprised if there was no nett outflow of air to the environment though.

Share this post


Link to post
Share on other sites
Posted (edited)

Think I'll combine the power and pressure switch wires into one cable that can go through a grommet in the base for sealing.  It could be Power(+13.8v), Gnd, SW1, SW2 with the switches connecting the lines to Gnd.  This would then be a 4 core cable, which I have.  Might use opto-isolators on the switch lines though not sure it's needed.  I used them where I was controlling the power for Peltier TEC and dew heater to isolate the RPi logic side from the power.

Core colour assignments could be :-

  • Red = +ve
  • Green = Gnd
  • Brown = SW1
  • White = SW2
Edited by Gina

Share this post


Link to post
Share on other sites
Posted (edited)

I should have some EL817 optocouplers but they're not in the components box where I thought they were.  I would like to err on the side of safety.

Edited by Gina

Share this post


Link to post
Share on other sites

With most of the ASC parts printed I thought I'd do a bit of testing before the pressure switch arrives tomorrow.  Attached the dome to the main body using the ring and 4 M3 screws.  Then I almost filled it with water.  Small beads of water started appearing over the printed body - so it leaks - badly.  I used ASA as that thermoplastic is supposed to stand up to UV better than others.  The previous casing was printed in PETG which at least kept the damp out for a few days.  Clearly, there is no point in better UV resistance over the years if it leaks.  PETG is renowned for interlayer bonding so it seems PETG is the filament to use.  Now to print a new casing in PETG then...

Share this post


Link to post
Share on other sites

Three quarters of the way through printing new casing.  New silicone sealant came in the post this morning.

551181511_Screenshotfrom2019-04-2918-14-54.thumb.png.d1485e56f81cbd7b1e8e777b2fcf62f6.png

Share this post


Link to post
Share on other sites

New casing printed in PETG - much stronger.  I used not only better filament type but also increased the extrusion and used solid fill.  The new casing is thicker, heavier and much stronger.  I tried a strength test.  I was able to destroy the previous casing by hand but not the new one.  Hopefully the new one will not leak when I test it.

Share this post


Link to post
Share on other sites

The pressure switch has arrived and clicks nicely with a bit of air pressure.  Next to connect to a water manometer and DMM to check pressure levels and which connections are which.

Share this post


Link to post
Share on other sites

Testing - lower pressure switch - ON at 5" and OFF at 4" approx.  Need a longed tube for the higher pressure switch.

Share this post


Link to post
Share on other sites
3 minutes ago, Gina said:

Testing - lower pressure switch - ON at 5" and OFF at 4" approx.  Need a longed tube for the higher pressure switch.

Typical switch and hysteresis values as I recall Gina. I remember getting into trouble when I adjusted the screws - the behaviour was not predictable as I recall as there was cross-coupling between the adjustments. I sure I forgot to mark them before fiddling!

 

Tony

  • Thanks 1

Share this post


Link to post
Share on other sites

I don't intend to touch the adjustments.   

I need to rig up the manometer better as the other switch has a large hysteresis and the switch contains quite a large volume of air compared with the 6mm ID silicone tube I'm using.  Initial results show switching ON at something like 6" and off at less than the other switch - maybe 2-3".  Only the OFF values are significant in this application.

Share this post


Link to post
Share on other sites
Posted (edited)

I've confirmed that the higher pressure switch (which I've called B) turns ON at about 6" and OFF at about 2".  

I have labelled the photo of the switch as shown below.  SW A turns ON at 5" and OFF at 4".  SW B turns ON at 6" and OFF at 2".

Terminals are :-

  1. NC
  2. Common
  3. NO

186506390_PressureSwitch01.png.b9e3009bc18aed1ab6997bd3e459ce8a.png

Edited by Gina

Share this post


Link to post
Share on other sites

I think I shall use the NO contacts and connect the switches to the main supply.  At the RPi I can either use optocouplers and series resistors to the LED and the TR to pull the GPIO line to data Gnd or simple resistive dividers connected to the GPIO lines and data Gnd.  I would prefer the first option though slightly more complicated.

Share this post


Link to post
Share on other sites

Decided to try the new silicone sealant on the dome.  Put a good layer in and screwed down the dome with the ring and M3 screws, then left it to set.  Later I tried submerging it in a bucket of water with plenty of air left inside.  It bubbled profusely round the edge of the dome!  :eek:  The internal pressure was about 6" of water.  I have since taken it apart again and reassembled using the bathroom silicone sealant.  I don't think that's quite as quick setting as the new sort so I'll leave it overnight before testing.

Share this post


Link to post
Share on other sites
Posted (edited)

I have now attached the base to the top of the casing with 8 M4 bolts and nuts with silicone sealant between the casing parts.  I'll leave it to set until tomorrow and then I can test for leaks.  I can see that the sealant has squeezed out all round the inside by looking in through the dome.  I have not put anything inside except the waterblock and a tissue to protect the dome from damage from it.  Cable and air pipe are sealed with grommets and the water pipes are a tight fit in tubular extensions to the base.

232126942_SealedCasing01.JPG.026a73bf66ff14f1f4fa22043080ad25.JPG

Edited by Gina

Share this post


Link to post
Share on other sites
Posted (edited)

Pipe junction for the pressurisation system.  Now printing.  Connects four pipes as follows :-

  1. ASC
  2. Air Reservoir
  3. Pressure Switch
  4. Air Input with Valve for applying pressure

1851434822_Screenshotfrom2019-04-3020-58-28.png.75f0cc301ecff1e25973c6d347c75f17.png

Edited by Gina

Share this post


Link to post
Share on other sites

I look forward to your repeat leak tests with interest Gina. I have notions about using 3D printed enclosure components myself on one of my own projects, with integral flanges and sealing cord grooves, that cannot be moulded conventionally. I will be guided by what you discover!

BTW - did you find the clear RTV sealant peeled easily off the PETG printed parts, or not? I am thinking about adhesion and possible issues in that area. Obviously the RTV evolves acetic acid and water during cure, but neither have any effect on PET so with some cure time should have no effect. On the other hand the so-called PETG filament is likely to be a proprietary blend with a few unspecified substances in the blend to improve lubricity, provide colour or whatever. There might be an issue there...

Best of luck when the cure is complete and you retest!

 

Tony

  • Thanks 1

Share this post


Link to post
Share on other sites

The clear RTV sealant peeled off the PETG easily.

Share this post


Link to post
Share on other sites

Had a thought - may be better to have two connections to the reservoir and blow air into that so that the desiccant in there can dry the air before it goes into the ASC enclosure.  eg. one tube going down into the bottom of the reservoir and the other at the top.

Share this post


Link to post
Share on other sites

I have a sort of test rig set up.  Printed a T piece (3 way) tube connector.  Took a 1L plastic bottle which compresses easily to increase pressure (waiting for bicycle valves to arrive today for that method) and drilled a hole in the cap for a grommet to take a silicone tube.  Connected bottle tube and ASC tube to T piece and T piece with another tube to the pressure switch.  Squeezed the bottle until the switch operated and held it at that.  It had detected a leak or leaks - the switch operated after less than a minute.  Just got some soapy water to find the leak.

Share this post


Link to post
Share on other sites
Posted (edited)

The results are in...  Problem is the T piece only.  Lots of bubbles there but nowhere else.  Tried soap solution everywhere (except pressure switch) and no bubbles.  Also, took complete ASC enclosure and immersed it deep in a bucket of water for several seconds and no wet appeared inside.  The dome was damp free once I had dried the outside with a kitchen towel.  I guess I need to seal the T piece with silicone or get the surfaces smoother.

Edited by Gina

Share this post


Link to post
Share on other sites

Trying a different 3D print layer arrangement to avoid grooves along the tube connections.

101015470_Screenshotfrom2019-05-0112-47-27.png.f684d10b950afb80559c8eb88cf8ad93.png

  • Like 1

Share this post


Link to post
Share on other sites
20 minutes ago, Gina said:

Trying a different 3D print layer arrangement to avoid grooves along the tube connections.

101015470_Screenshotfrom2019-05-0112-47-27.png.f684d10b950afb80559c8eb88cf8ad93.png

Nice!

I'm still new to 3D FDM printing and would not have thought of that!

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   1 member

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.