Langmuir-Probe-Fabrication

Table of Contents

  • 11 Materials
  • 12 Tools

    • Langmuir Probe Fabrication Procedures and Materials

    Figure a: Image of complete probe

    Figure b: Close up of a completed B-500-1-OR-Mod

    Figure c: Beginning steps of the stub and 1/8 NPT

    Figure d: Close up of a the completed stub, 1/8 NPT, and MDC BNC with the clamp

    1 Prepare the tubing.

    1.1 Cut a piece of 1/4" seamless stainless steel tubing into a 30" piece using a tube cutter.

    1.2 Deburr(smoothen) both ends of the tube until they are smooth (should be able to run tube across cheek without being scratched).

    Figure 1.2 Twisting the pipe back and fourth smoothens the inside diameter

    1.3 Polish the tube using a lathe and abrasive paper (400 and 600 grain).

    1.4 Use a tube bender to bend the pipe to the desired 90 degree angle, making sure to be carefule to not apply too much foce at once and bend the pipe to a smaller angle. AT ALL TIMES MAKE SURE THAT THE EXTERIOR OF THE PIPE IS NOT GETTING SCRATCHED.

    Figure 1.4 Tube bending device

    1.5 Measure your pipe from bent end to non-bent end and cut the non-bent end to have a probe of your desired length.

    1.6 Deburr the newly cut end.

    2 Install the B-500-1-OR-Mod on the tube (overview: see figure 4.0(TBD)).

    2.1 Fabricate a ledge on the 500-1-OR on the AS opening (the one closest to the hexagon). Widen the opening s diameter so that it is between 0.37-0.39 and is between 0.40-0.42 deep (a ledge will form, and DO NOT remove it) (see figure 2.1).

    Figure 2.1 B-500-1 without o-ing inserted

    2.2 Grease and insert a size 206 o-ring onto the obvious space for it on the 500-1-OR (on the side opposite the hexogon).

    Figure 2.2 B-500-1 without o-ing inserted

    2.3 Slide the 500-1-OR ono the pipe with the o-ring side facing the curved side of the pipe, meaning the hexogon is facing away from the bend in the pipe.

    Figure 2.3 What we have so far

    2.4 From the non-bent side of the pipe, slide a size 010 o-ing onto the pipe, followed by 2 small bumpers oreiented so that the sides wih smaller suface areas are facing eachother. And then slide on more size-010 o-ring, (pictured here).

    Figure 2.4 O-ring "sandwich"

    2.5 Slide on a silver bumper onto the pipe with its "skinnier side" facing the "o-ring sandwich" from step 2.4.

    Figure 2.5 Unskrewed cap

    2.6 Then slide on the silver cap with its skinnier side facing the rest of the hardware on he pipe, twist the cap onto the B-500 until finger tight, this will hide he o-rings and bumpers.

    Figure 2.6 Skrewed Cap

    3 Insert the 400-1 stub (overview: see figure 3).

    Figure 3 Photo of 400-1 stub

    3.1 Unscrew the nut on the 400-1 stub, removing the two ferrules from the nut. Slide the nut onto the tube, followed by the two ferrules (note: these next steps will need to be slid through the wire before they can be placed on the tube).

    Figure 3.1 Set up before getting skrewed

    3.2 Add the stub onto the tube, and then screw the nut on with the two ferrules in it until it is finger tight (note: it is not a tight fit and will fall off if not careful).

    3.3 Using a 1/2 and 9/16 wrench, tighten the nut and stub to lock it on the tube (note: this is irreversible, so double check all measurements before performing task).

    Figure 3.3 Langmuir-probe thus far

    4 Screwing in the 1/8 NPT

    4.1 wrap some teflon tape around the gnarling of the 400-1 stub, fully cover it once.

    Figure 4.1 Taped 400-1 stub

    4.2 Screw the 1/8 NPT on to the tapped gnarling with the larger flat end facin away from the curve in the pipe. Twist until finger tight.

    Figure 4.2 You may find it useful to utilize a clamp in oder to hold the probe in place while twisting the 1/8 NPT

    5 Preparing the alumina

    5.1 Take the piece of alumina and insert it into the bent side until it bottoms out and can support itself. Measure 4.5 inches from the base of the bend to some point on the alumina and cut the alumina at that point.

    5.2 Remove the alumina and set it aside.

    6 Wire the probe.

    6.1 Using the punch set, cut a 1/4" circle of tantalum and spot weld it to a 1" piece of gold plated nickel.

    Figure 4.0 Completed B-500-1-OR

    6.2 Strip one tip at one end of the wire and slide the alumina over the wire so that the stripped end sticks out.

    6.3 Spot weld the gold plated nickel to the stripped wires.

    6.4 Feed the excess wire through the tubing, starting at the bend and pushing it through. Continue to pull it until the alumina is snug in the tube and the tip is sitting snugly on the alumina tip.

    Figure 6.4 Wired probe

    6.5 From the much longer, unbent, part of the 1/4" pipe, feed about 12 alumina beeds around the wire in order to insulate the wie through the curved bit of the probe.

    6.6 Then feed in a longer peice of alumina aound the wire, making sure you have 3" of bare wire eposed when the long alimina if fed through and bottomed out.

    Figure 6.6 Nearly complete probe

    7. Large o-ring

    7.1 Slide a large, waxed, o-ring over an o-ring center. (pictured here)

    Figure 7.1 Waxed o-ring over center

    7.2 Place the large o-ring and and o-ring center combo on top of the flat end of the 1/8 NPT (Figure 7.3)

    7.3 Make sure that the wire in the 1/4 inch pipe is fed through the o-ring center with about 1" exposed

    Figure 7.3 How the probe should look at this point

    8. Welding the MDC BNC.

    8.1Spot weld the bare wire onto the couler pin on the MDC BNC and push the BNC onto the o-ring.

    8.2Use the clamp to secure the BNC, o-ring with center ring, and NPT together.

    Figure 8 A small, not to scale overview of the entire probe

      Materials

      • 1 Swagelok 500-1-OR (brass)

      • 1 Swagelok 206 o-ring (serial number unknown)

      • 2 Swagelok 010 o-ring (VT-7-OR-010)

      • 2 Swagelok back ferrules (SS-400-SET) NOTE: comes in a set with front and back ferrules, but only need the back ferrule (the smaller one)

      • 1 Swagelok Ultra Torr stub (SS-4-UT-6) NOTE: only need the pusher and nut, ignore all other pieces

      • 30 of 1/4 seamless stainless steel tubing

      • 1 Swagelok 400-1 (brass) NOTE: nut, ferrules, and stub all needed

      • 1 Duniway 1/8 NPT (KF16-1/8)

      • 1 Duniway o-ring with center ring (KF16-CR)

      • 1 MDC BNC connector (serial number unknown)

      • 1 small clamp (brand and serial number unknown)

      • Alumina tube (length adjusted as needed)

      • Wire (length unknown)

      • Tantalum sheet

      • Gold plated nickel wire

      • Teflon tape

      Tools

      • Tube cutter

      • Deburr tool

      • Tube bender

      • Wire strippers

      • Abrasive paper/sand paper (400 and 600 grit)

      • Lathe

      • Punch set

      • Spot welder

      • Applicators

      • Gloves

      • Bench vise

      • Safety glasses

    Spot Welding Tips and Settings: Unitek Peco 250 Dual Pulse Spot Welder

    Spot weld tantalum onto tungsten wire- Schedule: 5 Pulse #1: 5% Pulse #2: 15%

    Spot weld exposed wire onto MDC BNC- Schedule: 5 Pulse #1: 10% Pulse #2: 20%

    How to reprogram the spot welder 1. press [PROG] 2. use arrow keys and number pad to change pulses and schedule as needed 3. press [SAVE]

    last updated: summer 2018

    Authors: Jenny Collins, Greg Severn, & Miguel Magaña

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