Antares Analytical Technical Bulletin for February 2002

Subject: Loss of Optical Alignment Function

Relevant Models: All Baird MOA / FAS units … DV6 / DV6E ….. HA10 / HA12

Relevant Matrix: Not applicable

Symptoms:

• MOA / FAS / HA10 / HA12 No reading on the HG Meter when HG adjustment dial has been moved from last known HG peak alignment position.
• DV6 / DV6E – A reading of less than 10 counts when Optical Alignment is done and the correct sample is burnt and this doesn’t change as you rotate the optical alignment knob.
• HA10 / 12 and FAS2 / 2C users, please read the DV6 / 6E section because some details are similar to both product lines.

Current Unit Conditions:

• High Voltage is working
• Hg lamp is working (MOA / FAS) (HA10-HA12)
• Source is burning, Argon is flowing, and entrance optics solenoid is operating at the correct time (Expose)(DV6 / DV6E)

Most Probable Cause: DV6 / DV6E (see MOA / FAS / HA10-HA12 below) Optical alignment shaft connected to the Veeder Root Counter (VRC – optical alignment knob) has become disconnected from the entrance optics scan drive. This is a very common problem with the DV6 / DV6E.

Solution: Re-attach the optical alignment shaft to the micrometer head of the scan drive.

• 3 different number will be used to bring the optical alignment back into position.

1. The number written onto the micrometer housing when the unit was built at the Baird factory. This was written onto all DV6 / DV6E spectrometers in marker and will be located in a visible position on the micrometer housing
2. The intensity number shown on the screen, coming from the element being used for alignment purposes, while doing optical alignment. DO NOT use the bar graph shown on the screen as this is a very poor indication of optical alignment peak.
3. The number on the VRC. The number of the VRC is NOT directly related to the number written on the optical alignment housing because this VRC number will be adjusted later.

• Take the top cover off the spectrometer
• Looking down into the cell area you will see the flexible cable coming from the VRC. This is attached to a collar which fits over the end of the micrometer shaft. Usually the 2 set screws holding the collar to the end of the micrometer have become loose, letting the alignment knob turn free and not turning the micrometer shaft.
• Locate the number written in blue or black ink on the micrometer housing. This is the number for the actual alignment peak of the entrance slit to the grating / focal curve. Knowing the entrance slit / focal curve relationship is not important for this procedure.
• Be sure the collar is loose from the micrometer and rotate the micrometer to the number written on the housing. The micrometer number is meant to be the number written.
• Reattach the collar and tighten the 2 set screws. It is a good idea to use a SMALL amount of Lok-Tite type screw setting compound to prevent these screws from becoming loose in the future.
• Take off the black optical alignment knob, loosen the 2 set screws holding the alignment shaft to the VRC. Holding the flexible cable so it doesn’t rotate, rotate the VRC brass knob until the VRC reads 500. Tighten the 2 set screws and replace the black knob.
• Put on the top spectrometer cover and realign the unit as normal.

Probable Cause: HA10 / HA12 & FAS2 / FAS-2C

• The airpath HA10/12 and FAS2 / 2C are similar EXCEPT the FAS series entrance optics is also used with a background subtract system as part of the entrance optics assy. Otherwise regaining alignment peak is similar for both models.
• The HA10 / HA12 metal and oil systems will be the same are far as the entrance optics / entrance slit housing are concerned.
• As in the DV6 / DV6E models, the VRC is attached by a flexible cable to the entrance optics for alignment purposes.
• Unless specified, information is meant for both product lines.

Solution:

• In the HA series optical alignment is done by rotating the entrance slit, which is attached to the VRC flexible cable using a brass tooth gear / steel worm gear assembly located on the  entrance slit assembly. The entrance slit, which rotates, is mounted to a shaft which is attached to this brass gear.
• The FAS series, because of the background subtract system, has a fixed entrance slit and optical alignment is done with a deflection plate, in front of the entrance slit, mounted to this brass gear. The deflection plate rotates instead of the entrance slit.
• Turn off the high voltage and take off the top cover.
• Locate the brass gear (only one in the optical cell) and look for a line mark etched into the top of the gear. Then look for another line mark etched on the slit housing.
• Turn the VRC dial until these 2 lines are lined up side by side. This will be the approximate Hg alignment peak. There is no need to loosen the flexible shaft set screws to do this.
• If required, reset the VRC counter to 500 using the method using the procedure in DV6 section.
• Put the top cover back on, turn on the high voltage and realign as normal.

Probable Cause: All MOA models

• Same as FAS

Solution:

• Same as FAS but because of space limitations in the MOA optical cell, the marks on the top of the brass gear and entrance slit housing may be difficult to see. Best method is to use a flashlight and mirror for locating & aligning marks.
• Another possible cause (assuming everything else is working correctly) is a mis-aligned fiber optic cable. If you have changed motors, pulled down the stand for maintenance reasons, or in any other way moved the fiber optic cable, there is a good possibility this cable alignment has been disturbed. Contact Antares Analytical Services for further advice.

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