Antares Analytical Technical Bulletin for April 2002

Subject: Inaccurate Reference Result after a Routine Sample Analysis. (The MOA Topic “Sample Stand Fire Hazards” will be discussed later in this bulletin)

Relevant Models: All Baird DV, HA and FSQ series spectrometers with an MC20 readout system. All Labtest spectrometers with an MC20 readout upgrade. Source type is irrelevant.

Relevant Matrix: All ferrous and non-ferrous alloys with a reference percent greater than 50%. This will include steels, coppers, aluminum etc. Exceptions may include (depending on where your lower reference limit is set) certain Stainless Steels, Brasses, Zn Bronzes and Pb/ Sn solders.

Symptoms:

• An error message will be displayed “Reference Out of Limits”
• The reference percent will display as <75.0 % if you are using the MC20 reference limit default. Otherwise the “less than” percent will be whatever percent you have set your lower reference limit to.
• This problem will appear suddenly. This is usually not a problem which appears over time.

Current Unit Conditions:

• Normal burn cycle (flush, preburn, expose are operating correctly)
• Computer system is running correctly

Probable Causes: Loss of reference intensity used to calculate an element intensity ratio (I/R) for element (not reference) percent calculation.

Usually only one of the following is the problem.

• Optical Alignment (only if this occurs on the 1^st burn of the day or directly after optical alignment has been performed).
• Burning the sample in the wrong matrix (analyzing an Fe sample in an Al matrix for example)

• Burning in the source, but not in the sample stand (directly related to I/R output)

• Loss of high voltage, either on the reference element only or loss of high voltage to all the PMTs.

• Failure of measuring electronics.

• Failure of the entrance optics solenoid to open.

Background Information:

• The BAIRDAS software uses an Intensity Ratio (I/R) to calculate a percent value for all elements except the Reference Percent.
• The I/R is calculated by taking the direct intensity of the reference element and the direct intensity of another element, dividing them, multiplying by a constant factor and outputting the result as an I/R. If either the reference or element intensity is 0 or 1 then an I/R can not be calculated accurately.
• The reference percent is calculated using a “sum of the difference” method ….ie: in low alloy steel (for example) 100 – (C% + Mn% + P% ….) = Percent Fe.
• A reference element is never calibrated or standardized
• The “Reference Out Of Limits” message is always displayed when the reference intensity is out of the limits set in the software. BAIRDAS default limits are usually set at lower limit of 100 counts of intensity and an upper limit of 100,000 counts. 
• The reference % lower limit is always a default 75%, unless it was changed by the user during alloy calibration.
• All the other elements, because of no reference intensity, will report extremely high percents, thus using the “sum of the differences” to calculate a reference percent will always report below the lower reference limit percent.

Solutions:

To verify the reference intensity is the problem, do the following steps 1^st, to verify the reference is giving a low number (usually 0 or 1)

1. Burn a sample and after the result is given hit the ESCAPE button to get rid of the error message.
2. Using F9 for “menu” change the “burn mode” from Priority A (or whatever your usual priority is) and change to “Intensity.” This should change the results from a percent to a number. Notice the reference intensity.

If the reference intensity is less than 5 then check the following possible problems. If the reference intensity is over about 2000 and you still get a “Reference out of Limits” then contact Antares Analytical for advice.

1. Optical Alignment – Realign and be sure you have moved the VRC (optical alignment dial) to it’s peak location.

2. Wrong Matrix – Check for the correct matrix and burn the sample again.

3. Burning in the Source but not the Sample Stand – This is usually related to an argon problem. Check to be sure the argon tank has enough gas, the pressures are correct and the sample stand flowmeter (located on the lower front of your spectrometer) has sufficient pressure. Consult your manuals or contact Antares Analytical for correct pressures.

4. Failure of entrance optics solenoid to open:

·         DV 2 to 5: Behind the sample stand pull off the top triangle shape cover, start a burn and be sure the solenoid opens. If it doesn’t open please contact Antares Analytical for advice.

·         FSQ: You’ll need to listen for this sound because there is no easy to see the solenoid open. Turn of the source start a burn. Between the preburn and expose cycles you should hear a definite “click” coming from behind the sample stand. If you do not hear this “click” contact Antares Analytical for advice.

·         DV6: The DV6 solenoid is opened with argon pressure,  not an electric solenoid like the DV2-5, FSQ, HA series and Labtest spectrometers. If the DV6 solenoid doesn’t open, check the gas pressures and adjust, if needed, using the manuals.

5. Loss of the MC20 High Voltage Power Supply: This will cause the loss of high voltage to all the PMT’s. If this happens, all the elements will be an intensity of less than 5. To find WHY there high voltage supply doesn’t put out voltage (do not assume the supply is bad) refer to Antares Analytical Tech Bulletin of December 2001.

6. Loss of Reference Element High Voltage:  Swap another high voltage switching board from another slot NOTE: Be sure to turn off MC20 power before swapping boards. Turn on the high voltage power supply and try another burn in “Priority A” mode. If you do not get an error message and the reference percent is correct, replace the board.

7. Element Board Failure: Swap another element board, turn on the high voltage and try another burn as above. The same result and procedure as above. Contact Antares Analytical if a board is needed

8. Measure Board Failure: Again all the elements will read less than 5 in the Intensity Mode. Run the Electronics Tests with the source OFF. Pay attention to the Leakage Test because if all the number read the same number... usually 1 or 3 … this is a good indication the Measure Board, not the Element Board has failed.  

Subject:  Possible Fire Hazards in the MOA / FAS Sample Stand

Background: Over the years there have been several cases where a MOA sample stand has caught fire and burnt because of lack of cleanliness in the stand. This is a possible problem with all MOA / FAS as they age, but is especially possible when power plant fuel is being analyzed. The aluminum or plastic sample boats and the aluminum covers help to minimize the possibility, but most companies analyzing oil are using sample caps because of their low cost and no cleaning are required.

All operators are cleaning the sample electrode mounting areas but there are 2 places most companies pay little attention to.

Behind the green Phenolic plate which the electrode assembly is mounted on is an area which, over time builds up a large film of oil and dirt. Since there is power going to the motor mounted in back, this can create a possible fire hazard. The best time to clean this is during a scheduled Service Call when a Service Engineer can pull down the stand and clean behind it.

Pulling this stand down should not be done by untrained personnel because removing this Phenolic plate involves removing the fiber optic cable. Once this fiberoptic cable is removed it must be realigned precisely,  with the correct tools and procedures or you will lose your optical alignment. This is guaranteed to happen if this F/O cable is not replaced and realigned exactly. A qualified Service Engineer will have the correct tools and experience to do this.

Probably the most hazardous place for a possible fire is on the stand door. The foam covered RF shield on the door, over time, becomes soaked with oil, dirt and grime. This foam shield is only a  few millimeters from the sample as it is burning during the analysis cycle and the possibility of a sample flaming up and the foam catching is there.

This foam RF shield can not be cleaned, is easily replaced by the customer and is readily available. The cost is not large so, it is suggested this foam RF shield be replaced when it becomes oil and fuel soaked. The MOA is no longer being manufactured which means the cpmplete sample stand, or it’s major components, are no longer available.

Even when it was available, the stand had a price of over $10,000 + installation costs and some customers were put to this expense because their sample stands burned up. Antares Analytical’ s suggestion is to avoid the possible loss of the MOA by taking the above steps to minimize a possible fire.

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