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I have a plastic ABS project enclosure which I'm trying to figure out how to mount a sensor to the inside of, against a window that will be placed into the enclosure wall so that it looks through the window and is as close to and stable against the window as possible. I'd like to avoid gluing the sensor -- if that's even possible -- for maintenance reasons.

The sensor is a LWIR sensor in a TO-39 can.

TO-39 sensor

I'm trying to avoid soldering wires to its leads so I plan to use a socket with wires soldered to the socket's leads.

Socket

The link is a TO-100 socket, but with the appropriate diameter and spacing (though an extra 4 sockets).

My plan is that I'll have the TO-39 can on top of the pictured socket.

How do I "attach" those up against the inside of the window in the plastic enclosure? The enclosure will be outside and waterproof, so I'm trying to avoid putting holes in it which I'd need to seal. Also, the window will be quite small. Thus I prefer to glue something to the inside of the enclosure which surrounds the window.

I'm thinking of something like a z bracket:

z bracket

But that doesn't seem ideal because:

  1. the bracket needs to hold the socket somehow.
  2. bracket needs to be attachable (gluable?) to the enclosure wall
  3. be somewhat adjustable because it's unlikely that I'll find a bracket the precise number of millimeters to keep the sensor against the window.
  4. Ideally serviceable in a way that the sensor can be removed

Maybe some sort of bracket glued to the inside of the enclosure but with a rubberband which pulls the sensor toward the window. If I could use 2 or 3 rubberbands then they'd fit through the socket's leads and keep the socket stable?

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  • \$\begingroup\$ Glue something to the cabinet that is thick enough to drill into without going through. Perhaps put bolts through something like that from the cabinet side before gluing it on. Use a spring or springs rather than rubber bands. Solder the socket to a small project board. \$\endgroup\$ – Charles Cowie May 29 '18 at 23:10
  • \$\begingroup\$ That looks like a temperature sensor, so I assume your window must be a special material transparent to thermal IR, not glass or acrylic. \$\endgroup\$ – Henry Crun May 30 '18 at 1:18
  • \$\begingroup\$ I think it's a gas sensor and the window will be a hole. \$\endgroup\$ – Jasen May 30 '18 at 7:54
  • \$\begingroup\$ This is borderline ME rather than EE. \$\endgroup\$ – Reinderien May 30 '18 at 8:13
  • \$\begingroup\$ It's an LWIR sensor, so the window will be Si or probably Ge, though it'll be small, so I've been planning to attach to the surrounding ABS enclosure. \$\endgroup\$ – James S May 30 '18 at 14:05
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The best glass bonding compound I have worked with is silicone RTV, but the ammonia vapors can corrode metals, so I used RTV 120 series which has almost no ammonia in it.

Glass expands and shrinks with temperature so most epoxies and cements will let go on the first freeze/thaw cycle. We used white but like most RTV compounds you have a choice of colors.

The non-ammonia type has 50% of the holding power of regular RTV, and the manufacture recommends 24 hour cure time, 48 hours till full hard cure.

Even at 50% strength, it is tough to pull off of glass or shiny stainless steel.

RTV 122 White

RTV 123 Black

RTV 128 Translucent

Key Performance Properties:

• Primer less adhesion to many metals and plastics*.

• Non-corrosive to aluminium and steel per MIL-A-46146A+.

• Lower odour cure than conventional acetoxy silicone sealants. • UL Recognition. Recognized by Underwriters’ Laboratories, Inc. under their Component Recognition Program (UL File No. E-36952). Refer to GE Silicones Tech Info Sheet CDS4320 for additional information.

• One component.

• Cures at room temperature.

• Excellent electrical insulation properties.

• Retains elastomeric properties at temperatures of -60C(-75F)

to 204C (400F) for long periods and to 260C (500F) for short periods.

• Excellent weatherability, ozone, and chemical resistance.

This is the link to the pdf.

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    \$\begingroup\$ That looks like a temperature sensor, so I assume the window must be a special material transparent to thermal IR, not glass or acrylic \$\endgroup\$ – Henry Crun May 30 '18 at 1:24
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If you machine the window out of transparent plastic, you can make it extra thick and provide mounting bosses for a transition PCB between the sensor socket and conductors to your main PCB. If you consider the PCB-sensor a replaceable "module" you could avoid the TO-39 socket entirely, which would be nice.

Then the problem reduces to attaching and sealing the window to the box. If the inside of your enclosure is smooth enough you could machine a groove into the facing part of the window and use an O-ring, with similar grooves/O-rings for mounting screws etc.


If you are unable to make a window of a suitable material, then consider just mounting the sensor to a machined block which is then mounted to the enclosure and PCB as suggested. It appears that HDPE and polyolefin plastics are suitable for some IR applications.

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maybe something like this

drill hole in bracket to fit the sensor

a nylon quicktie could be used instead of a retaining clip

enter image description hereenter image description here

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solder the socket into a printed circuit board and bolt the board to the case using countersunk machine screws and spacers and nuts.

enter image description here

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  • \$\begingroup\$ Why'd you specify countersunk? I want this to be weatherproof so I'm trying to avoid putting holes into the enclosure. Does countersunk help with weatherproofness at all? \$\endgroup\$ – James S May 30 '18 at 14:14
  • \$\begingroup\$ I chose countersunk because it looks tidier, but because it finishes flush you can cover the screw head with aluminium adhesive tape (or similar) to make it weathertight. \$\endgroup\$ – Jasen May 31 '18 at 1:27

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