Antares Analytical Technical Bulletin for September 2003

Subject: FSQ or DV2-5 Loss of Optical Alignment

Relevant Models: All Baird FSQ and DV2, DV3, DV4, DV5 models

Relevant Matrix: Not applicable

Symptoms:

• DV2, DV3, DV4, DV5 No reading on the HG Meter when HG adjustment dial has been moved from last known HG peak alignment position.
• FSQ,  A reading of less than 20 counts when Optical Alignment is done and the intensity doesn’t change as you rotate the optical alignment knob.

Current Unit Conditions:

• High Voltage Power Supply is working correctly
• Hg lamp is working correctly

Background Information: Optical alignment in the DV series and the FSQ is done by moving the entrance slit sideways to the grating. This causes the optical spectrum to “shift” across the grating which causes the spectrum to move side to side on the fixed exit slits. This movement is what causes the “bell” shape of the optical alignment scan and the slit scans.

Possible Causes:

DV series: The DV2-5 (and DV6) entrance optics has the entrance slit mounted on a movable assembly. This assembly is located in the vacuum cell, behind the sample stand, and can only be gotten to by releasing the vacuum in the cell and opening the cell door.

• One side of this assembly is attached to the vacuum cell housing using a flat spring steel mounting plate. This spring steel mounting plate allows some horizontal movement of the entrance slit assembly, but also provides the needed tension to keep the slit assembly in place.
• The other side of the this assembly is attached to the exterior micrometer assembly with a coil spring. This coil spring pulls the slit assembly away from the spring steel mounting plate, which is providing tension. It is a “pull – pull” on opposite sides of the slit assembly.

Problem: It is common for this coil spring to disconnect from the micrometer shaft or the slit assembly. When this happens, the entrance slit is allowed to be pulled all the way to one side of it’s travel and remain there.  Solution: It is necessary to open the cell and reattach the coil spring. This is fairly simple to do as each side of the spring is mounted in a small hole.

Problem: The Hg mirror solenoid is not closed completely. The entrance mirror solenoid is mounted above the argon flushed chamber directly behind the sample stand and is accessible by taking off the small triangular cover above the sample stand. The solenoid shaft connects to a small pin which causes the Hg mirror to close after expose. Closed, or the Hg mirror allowing the Hg light into the entrance optics, is it’s normal state. During expose, this solenoid opens and allows burning sample light to pass into the vacuum cell. Over time this small coil spring on the solenoid can become weak, so the Hg mirror does not close all the way “home.”  Solution: The coil spring must be removed and carefully stretched a small amount. This will give the spring enough power to completely close the Hg mirror after expose. NOTE: Be careful because pulling this spring to far will cause the Hg solenoid NOT to open during expose. This will create analytical problem of it’s own, so after stretching and installation, a complete analytical cycle should be run to make sure the solenoid opens and closes completely.

Problem: The Hg mirror has fallen from it’s mount. Solution: The plate which mounts the Hg solenoid can be gotten to by removing the 4 bolts holding the Hg mirror assembly to the optical cell. This allows the entire Hg mirror assembly to be removed. Assuming the mirror has fallen off, it will by lying on the bottom of the argon chamber below. The mirror can be remounted on the plate using any strong commercial glue .. 5 minute epoxy is suggested for strength. After drying the Hg solenoid assembly is put back in place and bolts reattached. No special physical alignment is needed.

Other possible causes: Failed Hg amplifier board or failed Hg meter on the panel. Please contact us for more information on these,

FSQ Series:  The FSQ uses a slightly different procedure to move the entrance slit.

·         On one side of the entrance slit assembly spring steel is used to PUSH … not pull … the entrance slit assembly away. The other side is the shaft which is attached directly to the Hg alignment know. As the optical alignment dial is rotated, this shaft pushes on the entrance slit, depressing the spring steel and increasing the resistance of the flat spring. The FSQ uses a “Push – Push” procedure to move the entrance slit, while the DV uses a “Pull – Pull” to accomplish the same thing.

·         The Hg slit assembly for the FSQ is totally within the vacuum cell

·         The causes for the FSQ losing optical alignment are similar to the DV series, though repairing will be more difficult because of the design of the FSQ.

·         If a problem with the Hg mirror or solenoid is suspected, please contact Antares Analytical for more specific troubleshooting help. These components are located directly behind the Sample stand and getting to them requires taking down the sample stand … something NOT recommended without expert guidance. The concern here is not taking down the stand, but reinstalling the stand. Unless this is done EXACTLY you will lose all optical alignment. This is almost a GAURANTEE.

·         The FSQ does not use a Hg amplifier, but passes the Hg signal through the standard MC20 readout electronics. Please contact us for more information regarding possible problems with the MC20 electronics.

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This Technical Bulletin is edited by Gerry Smith, Technical Services Manager of Antares Analytical. Having spent 25 years working with Baird spectrometers (22 years with Baird Analytical in various capacities, including many years as Final Test / Calibration Manager and Senior Service Engineer, International Operations) he or any of our Technical Support Staff, are well qualified to answer any Technical or Applications problems you may have.

For further information or access to past monthly Technical Bulletins covering a variety of subjects, please  visit our website (still under development) at www.antaresanalytical.com .For more information, to be added to this list,  or help with other subjects including Tech Support, spare & replacement parts, or on-site Service by qualified Antares Analytical Service Engineers, please contact us at info@antaresanalytical.com 

This bulletin is meant for informational purposes only and it not meant as a substitute for Service performed by a qualified Service Engineer. Any use of this information is done strictly at the discretion of the user. Antares Analytical, nor any of it’s employees or Partners, is not responsible for any misfortune which results as the result of use of these Technical Bulletins, in place of service by a Qualified Service Engineer.