Antares Analytical Tech Bulletin

April, 2003

Problem: No Burning in the MOA / FAS Sample Stand  This Tech Bulletin will deal only with the most common cause of this problem: A faulty “Source On” Interlock System.

Relevant Models: MOA / FAS (all models: MOA-C …MOA-GT …. MOA- C/GT …Mil MOA), HA10/12 configured as Oil Analysis unit, older DV2 models with the Oil Analysis Module as a “2nd stand.  Information about this problem, as it relates to Baird metal spectrometers (DV, FSQ etc) can be found in the November 2001 Antares Technical Bulletin.

Relevant Matrices: Oil and Fuel Analysis

Background Information: The MOA source is designed to give constant, controlled & regulated,  high voltage DC power to the analytical gap for sample excitation. The source circuitry is a simple, well designed and rugged package, manufactured to US DOD Mil-Spec qualification, and will provide years of trouble free operation, when maintained and operated correctly. The MOA source / stand come in several configurations depending on the type sample being analyzed.

This Tech Bulletin will deal only with the MOA / FAS systems. Users of  HA10 / 12 or DV2 with an oil stand should contact us directly for further information.

System Interlock Failure: As said above, the most common cause of no burning in the sample stand is a defective interlock switch or failure of the interlock circuitry. The  function of this interlock system is to insure the door is closed burning sample analysis because:

  1. The sample burning puts out a large amount of bright UV (ultraviolet) light which can be damaging to the eyes.
  2. The high voltage across the analytical electrodes is approximately 22,000 VDC @ 2-4 amps and can be fatal.
  3. The high voltage arc across the electrodes emits an amount of RFI (radio frequency interference) which can cause problems with the measuring electronics and can possibly, over long exposure, have an affect on the human body when in close proximity. This is part of the reason for the Lead Mesh shielding built into the sample stand door and the RF shielding around the door frame of the MOA.
  4. As the sample is being analyzed, a fire hazard is possible by the burning sample. Generally analyzing a sample will not cause problems, but certain samples (especially power plant fuels when used with the MOA GT) can catch fire. In the event of  “flaming” of the sample, the closed door will limit any possible damage, to the interior of the MOA sample stand. For more information please see Antares Technical Bulletin of April 2002: Fire Hazards in MOA / FAS Sample Stand.

Source Interlock Operational Description:  This interlock system “turns on” the MOA source by providing a safety circuit the 110 VAC to power the various source functions needed to spark the oil / fuel sample in the MOA sample stand.

 

  1. The Interlock system uses the 110 VAC generated by the closing of the K2 “source on” relay. This K2 “source on” relay is located on a small circuit board, on the floor of the MOA electronics cabinet and should not be confused with K1 / K2 relay located in the source chassis.  This K2 relay is closed by a signal from the MOA control electronics, when the burn switch is pushed.
  2. Closing of the K2 relay allows 110 VAC to pass through the K2 closed contacts, through the closed door interlock switch, and into the MOA source closing the contacts of the K1 power relay.
  3. It is the K1 power relay which supplies power, through 3 sets of contacts, to A) the blower fan inside the source, B) the disc electrode motor inside the sample stand and C) power to the Pulse and Ignition circuits.
  4. It is the Pulse & Ignition circuits which sparks the oil / fuel sample at the analytical gap. If either the K1 Power Relay (source chassis) or the K2 “source on” relay (located on the card on the electronics cabinet) fail to close … the source will not fire. 

Troubleshooting and Repair:

  1. The most common failure of the interlock system will be failure of the interlock switch located on upper right corner of the MOA sample stand door frame. This is an “ON-OFF-ON” switch which is always OFF when the door is open.
  2. When the door is closed the switch will be pushed into the ON position (the switch is spring loaded and will always go into the OFF position when the door is opened), the interlock circuit will be completed and the source will burn when the Burn switch is pushed.
  3. The 2nd ON position is:  when the stand door is opened the switch button can be pulled out and should lock into place. In this position the source should also fire. THIS SWITCH POSITION IS ONLY TO BE USED FOR TEST PURPOSES. CONSTANT USE IN THIS SWITCH POSITION, BECAUSE THE SAMPLE STAND DOOR WILL BE OPEN, WILL RESULT IN DAMAGE TO THE SPECTROMETER, AND / OR POSSIBLE INJURY OR DEATH TO OPERATING PERSONNEL.
  4. After all appropriate safeguards are taken (no personnel near the sample stand electrodes, eye protection GLASS ONLY … not plastic etc.)  …. with the door opened, disc & rod electrodes in the stand and NO SAMPLE IN THE STAND.
  5. Pull the switch out until it “clicks.” The switch will stay open and the interlock switch is now “ON.”
  6.  WARNING: For the next step the source will start and the following will happen A) the source will start a burn across the analytical gap and there will be a BRIGHT ARC across the electrodes … DO NOT look at this light directly unless wearing GLASS eye protection (eye protection from strong UV light),  B) The electrode motor will start to rotate the disc electrode and C) The blower motor in the source will start to rotate. NOTE: “blower motor” means the motor fan inside the source which blows air across the Auxiliary Gap. This is not the exhaust motor located above the sample stand.

If 1 or more of these 3 things do not happen immediately hit the Stop / Reset button and check the following:

  1. The switch is in the pulled out position.
  2. The main power in on the MOA and Ready / Standby switch is in the Ready position
  3. Fuses F6, F7 and F10 are good. These fuses are located at the fuse panel on the right side of the spectrometer.

If the source now fires:  close the door and try to start the source again. If the source fires with the door open and interlock switch in the pulled out position but not with the door closed. This is a good indication you have a bad switch. Replace the switch.

If, after checking all the above:  the source still does not fire and / or the disc electrode motor does not rotate then:

  1. Turn off all power to the spectrometer and remove the power cable.
  2. Using an ohm meter check for continuity of the switch contacts in both “ON” positions. If no continuity is found, replace the switch.
  3. If continuity is found then the problem is somewhere else in the “Source On” circuitry and that will be covered in the May Antares Analytical Tech Bulletin.

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This Technical Bulletin is written by Gerry Smith, Technical Services Manager of Antares Analytical. Having spent 22 years with Baird 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 

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