Langmuir-Probe-Fabrication

Table of Contents

Langmuir Probe Fabrication Procedures and Materials

Figure a: Jenny Collins with the installed probe

Figure b: An overview of the entire and completed Langmuir probe

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

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

Figure e: 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 both ends of the tube until they are smooth (should be able to run tube across cheek without being scratched).

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

1.4 Place the tube vertically in a bench vise and use the tube bender to bend the tube to the desired angle (see figure 1.1). IMPORTANT: to prevent the tube from scratching while in the vise, use a rag or paper towels to protect the part being held by the vise.

Figure 1.1 Tube bending specifics

1.5 Remove the tube from the vise, then replace it in the vise horizontally, using the same protective process as above in 1.4, with the bent end hanging out from the vise (see figure 1.2). Measure the tube from the highest part of the bend, measuring it out to be 22¼-22½ , then mark the spot. Use the tube cutter to cut the tube at the point of the mark.

Figure 1.2 Placing the tube in the bench vise without scratching the surface

1.6 Deburr the newly cut end.

2 Prepare the alumina.

2.1 Take the piece of alumina and insert it into the bent side until it bottoms out and can support itself. Measure 4" from the base of the bend to some point on the alumina and cut the alumina at that point (see figure 2.1).

Figure 2.1 Measuring and cutting the alumina so it fits correctly

2.2 Remove the alumina and set it aside for later use.

3 Wire the probe.

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

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

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

3.4 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.

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

Figure 4.0 Completed B-500-1-OR

4.1 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 4.1).

Figure 4.1 Dimensions and diagram of the fabricated changes added to the Swagelok 500-1-OR

4.2 Grease and insert a size 206 o-ring onto the 500-1-OR, on the non-fabricated, or VS, side (there will be a clear indentation for the o-ring to fit into) and place the 500-1-OR on the tube (placement tip: the distance from the beginning of the installed o-ring to the longest point on the bend should be 19½-19¾") (see figure 4.2).

Figure 4.2 Measuring the tube after adding the B-500-1-OR

4.3 WORK ON THE A.S. SIDE FOR STEPS 4.3 AND 4.4! Add a size 010 o-ring onto the tube, followed by a back ferrule (flat side facing the o ring), followed by another back ferrule (with the flat side facing away from the other ferrule), and followed by one additional 010 o-ring (see figure 4.3)

Figure 4.3 The order of the o-rings and back ferrules added to the tube

4.4 Insert the UT SS-4-UT-6 pusher on, with the smaller end pushing against the first o-ring, followed by the UT nut. Push it all together and screw the UT nut until it is finger tight.

5 Insert the 400-1 stub (overview: see figure 5.0).

Figure 5.0 The overview of the 1/8NPT and MDC BNC

5.1 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).

5.2 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).

5.3 c 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).

6 Screw the 1/8 NPT onto the open end of the 400-1 stub, using Teflon Tape on the stub threads, until finger tight (see figure 5.0).

Figure 5.0 The overview of the 1/8NPT and MDC BNC

7 Grab the excess wire on the AS end and begin to wrap it in very tight circles, about 6 times around. Then, interlock it, to form a toroid of wound wire. Insert it in the small opening of the 1/8 NPT (note: you will want some amount of excess wire still remaining free).

8 Slide the o-ring with center ring through the wire and push it until it fits snugly in the opening on the NPT.

9 Insert the MDC BNC (overview: see figure 5.0).

Figure 5.0 The overview of the 1/8NPT and MDC BNC

9.1 Cut the wire on the AS end, so that a small amount sticks out from the o-ring.

9.2 Remove the o-ring and strip the wire from the base of the NPT to the tip.

9.3 Slide the o-ring back on to the NPT.

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

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

Figure A A small, not to scale overview of the entire probe inside the machine, including all dimensions and measurements

    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 gold plated nickel- Schedule: 5 Pulse #1: 5% Pulse #2: 20%

Spot weld gold plated nickel onto exposed wires- Schedule: 5 Pulse #1: 5% Pusle #2: 15%

Spot weld exposed wires 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]

Date: 2013-07-22 08:26:08 Pacific Daylight Time

Author: Jenny Collins, Greg Severn

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