Tag Archives: ion gauge

Ion gauge coated ceramics

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Ion gauges work by using a hot tungsten filament to ionize gas molecules and then collect the ion current and convert that current to a reading in Torr, Pascal or millibar.

Over time the ceramics on the ion gauge feedthrough can become coated with tungsten or titanium. That coating is conductive and when the coating covers the entire length of the feedthrough then the resulting leakage current can affect the accuracy of the ion gauge or prevent it from working at all. The picture below shows an example of a coated ion gauge.

Usually once the ceramics are fully coated then the ion gauge needs to be replaced at a cost of $500.00 or more.

This blog post will show you how to remove the coating from the ceramics and restore normal operation of the ion gauge for about $15.00

The first thing that you will need to do is to buy some dental polishing tape.  I used some TDV diamond strips as shown below. You can get diamond polishing tape on Amazon.

With the filaments removed from the ion gauge, mount the ion gauge in a vise.  The ion gauge needs to be tight but not so tight that the flange warps.

Use the diamond strip in a back-and-forth motion to remove the coating from the ceramic.  Use a light touch as you want to remove the coating but not eat away at the ceramic any more than necessary.

Once you have the ceramic cleaned off, use a soft paint brush to clean the grid and to remove any small bits of ceramic from the flange. Note that all of the deposition does not need to be removed, but you want enough so that there is a gap on the ceramics which will eliminate any leakage current. The picture below shows the results after a few minutes of cleaning. Not very pretty, bit it does restore functionality.

Install a new filament set and you are good to go!  RBD Instruments sells ion gauge filaments for the PHI DGCIII controller.  Contact us for more information.

How to clean a nude ion gauge

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The ceramic feedthroughs on the nude ion gauges commonly used in vacuum chambers can become coated over time which results in non-accurate or unstable readings.  The following procedure can be used to clean the coating off of the ceramics.  Install a new filament assembly on the clean feedthrough flange and voila! – You have a rebuilt ion gauge.  RBD provides the filament assemblies for a wide variety of ion gauges.  If you can’t or don’t have the time to clean the feedthrough assembly on your coated ion gauge, RBD also provides complete ion gauges at great prices. The RBD Instruments ion gauge filaments and complete gauges can be found at this link – Low Cost Ion Gauge Filaments

 

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cleaned-ion-gauge-feedthrough

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Ion gauge cleaning procedure

Note: This procedure can be used to clean the tungsten and carbon coating off of the ion gauge ceramic feedthroughs. It is not intended for ion gauges that are contaminated with oil. If your ion gauge is contaminated with oil it should be replaced.

  1. Tape a used gasket to the flange. This is to ensure that the knife edge is protected (rule # 1).
  2. With the ion gauge flange pointing down, sandblast the ceramics with clean alumina. Avoid the grid.
  3. With the ion gauge flange pointing down, sandblast the ceramics and metal can with clean glass beads. Avoid the grid.
  4. With the ion gauge flange pointing down, move the sand blast nozzle as far away from the ion gauge as possible and sand blast the grid lightly with clean glass beads to remove any black contamination from the grid. You not want to get the nozzle too close to the grid as the air blast will damage the grid and or bend the collector wire.
  5. Shake off any excess blast material.
  6. Rinse off the ion gauge flange with water.
  7. If necessary, straighten any of the grid wires that may be bent out of position
  8. With the ion gauge flange facing down, place the ion gauge into a beaker filled with 5% Alconox or another lab detergent and water. Ultrasonic for 5-10 minutes. Warm water works best.
  9. Remove from beaker and rinse well with water.
  10. Place ion gauge flange face down in a beaker of DI water with no soap.
  11. Ultrasonic for 5-10 minutes
  12. Remove from water and rinse thoroughly with DI water.
  13. Dunk once into Isopropanol (to remove the water).
  14. Blow off excess Isopropanol (especially from inside the cap where the collector wire is located) and then dry in an air oven for 1 hour at up to 200C.
  15. Install new filament assembly.

Rebuild is complete!

When you install the ion gauge back into your vacuum chamber you will need to run it through one or two degas cycles.

Also check out the RBD Techspot blog post on how to install an ion gauge filament.

How to test an ion gauge filament

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This post will explain how to test and replace the nude ion gauge filament assembly on a Physical Electronic (PHI) X-ray photoelectron, Auger electron or SIMS system. Look at the pictures at the bottom of the post before you read the procedures.

Background – On most PHI surface analysis systems the ion gauge filament is located either above the table tops in back of the vacuum chamber, or just under the tabletops.  The newer (as in less than 30 years old) systems have a cover that protects the user from the exposed electrical connections to the ion gauge pins. On the oldest PHI systems the ion gauge pins are exposed, but located under the table tops and difficult to access (and so relatively safe).

Here are links to some videos that explain how an  ion gauge works –

https://www.youtube.com/watch?v=IKKuWeEShM4

https://www.youtube.com/watch?v=6zv_Y0_vwsg

How to measure the resistance on the ion gauge:

  1. Turn off the DGCIII (or other brand of) ion gauge control.  This is not only the first step; it is the most important step! Ion gauge controls such as the DGCIII used on older PHI systems have about 200 volts of DC on the grid. If you do not turn off the DGCIII (or other) ion gauge control before removing the wires to the ion gauge you will likely receive a potentially lethal electrical shock. If you are not familiar with working safely with electricity then refer this procedure to qualified personnel.  Or, turn off the DGCIII and also and also unplug the 120 VAC power cord on the back of the DGCIII and then there is no danger of electrical shock.
  2. Loosen the set screws on the shield retaining collar. Do not loosen or remove the bolts that connect the ion gauge to the system! See the pictures at the bottom of this post for clarification.
  3. Loosen the strain relief screws and slide the shield out and away from the ion gauge, being careful to support the wires.
  4. Using an 048-4 spline wrench, loosen the ion gauge coupler set screws by turning the set screws closest to the flange CCW 1 to 2 turns and then gently pulling the coupler and wires off of the ion gauge pins. TIP: As you remove the couplers turn the set screws CW 1 turn so that they do not fall out of the couplers. RBD provides the 048-4 spline wrench and the setscrews.
  5. Use an ohmmeter and measure the resistance between the center filament pin (common) to the outside two filament pins. See the picture below. The pins resemble a smiley face and the filaments are the smile. The grid is the eyes (some ion gauges have 2 grid pins, some only one), and the collector is the center pin (nose). The filament resistances should be 1 ohm or less when measured from the center filament post to the outside two filament post. If a filament is burnt out (open) then the resistance will be infinite or some high value if there is a tungsten coating on the filament base.
  6. If one filament is burnt out but the other one is good, then you can switch filaments.  If you have 3 wires connected to the filaments then swap the outside two filament connectors. If you have just two filament wires, then move the outside filament wire to the other side.
  7. If both filaments are open, then the filaments need to be replaced. See the replacement procedure in the following section.

ion-gauge-wire-connection-types

ion-gauge-wire-connectionsHow to replace the ion gauge filaments:

  1. Vent the chamber.
  2. If not already done, remove the connectors from the ion gauge as per the previous procedure.
  3. Remove the bolts from the ion gauge flange.
  4. Remove the shield retaining collar.
  5. Carefully remove the ion gauge.
  6. Loosen the top set screws on the 3 filament base connectors. These are typically .050 hex screws.
  7. Remove the old filament assembly.
  8. Install the new filament assembly and tighten the set screws. Make sure that the filaments are parallel with the grid.
  9. Use a new copper gasket and place the ion gauge up to the flange. Make sure that the filaments are facing down. They will not line up perfectly parallel, so just choose the best position where the bolt holes line up. By facing the filaments down you will prevent any debris from falling onto the grid which may short out and damage the ion gauge control.
  10. Place the shield retaining ring up next to the ion gauge flange and rotate it so that the set screws in the shield retaining ring are accessible.
  11. Insert the bolts and tighten the flange.
  12. Reattach the ion gauge couplers. Make sure that the pins are bent slightly in towards the center collector wire so that none of the pins will short to the shield when it is installed.
  13. Carefully slide the shield over the wires and press the shield firmly into the shield retaining collar.
  14. Tighten the shield retaining set screws.
  15. Slightly tighten the strain relief screws.

That’s it!  Pump the system down and the ion gauge is ready to turn on once you get into the 10-4 Torr or better vacuum.

RBD Instruments provides replacement filament assemblies, complete ion gauge assemblies and the required spline and Allen wrenches. Contact us for more information.

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