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    The SVP Bombarding Temperature Gauge is the only instrument of its kind on the market specifically designed for high voltage luminous tube processing. It is unaffected by the high voltage electromagnetic field (corona discharge) produced by the bombarder as are other types of instruments and mediums.

    The Simpson Self-Shielding Annular Pivot & Spring-Loaded Jewels meter assembly is the highest torque to weight ratio meter available. The meter assembly is enclosed in a PVC meter box and is completely self-powered. It does not require batteries or other electrical source to function.

    The temperature sensor is a clamp-on unit, which ensures positive contact with the glass. The sensor is encapsulated in a heat sensitive glass fiber material that protects the sensor from oxidation. The thermocouple wire is sheathed in high temperature silicone rubber tubing rated at 600F and is 60 long. This allows stationary placement of the instrument without having to move it with each processing cycle. (Custom lengths are available)

    The large 4 meter face is easy to see and truly unique. It provides the processing technician with at-a-glance information during the heating stage as well as the glass cool- down stage - something other gauges, crayons and paper simply cannot do.

    A bombarding temperature gauge is one of the four instruments essential for proper luminous tube processing. A specific glass temperature is necessary to insure that the maximum amount of contaminants and impurities are released from the internal surface of the tubing. If allowed to remain, these impurities will affect the life, efficiency and overall quality of the finished unit. In red tubes excessive impurities will cause premature failure. In mercury discharge tubes it will cause premature and unnecessary staining and discoloration. Therefore, a specific glass temperature allows for highly effective degassing of the tube and at the same time ensures that the glass is not overheated, which may damage phosphor coatings and the glass structure.

    The SVP Bombarding Temperature Gauge is unique from other meters/gauges and methods. In addition to being unaffected by the high voltage corona discharge produced by the bombarder as are other instruments, crayons and mediums, the meter face has specific markings for the heating stage that correspond with most electrode manufacturers bombarding recommendations. The meter face also incorporates specific markings to compare glass cool down temperatures with the speed of evacuation* following the bombarding cycle**. This ensures that the unit is being evacuated at a fast enough rate compared to specific glass temperatures to ensure that re-absorption of the contaminants released during bombarding does not occur. (The temperature at which re-absorption begins is approximately 175C as the glass cools***.) The large 4 analog meter face in conjunction with these specific markings provides the processing technician with at-a-glance information as opposed to trying to focus on rapidly changing digital numbers during the critical stages of processing, or guessing at what the glass temperature may be if a temperature gauge is not used at all.

    * In addition to the SVP Bombarding Temperature Gauge, a high vacuum gauge is necessary to accomplish the comparison between glass cool down temperatures and the vacuum levels obtained.
    ** SVP Neon Equipment is the only equipment manufacturer who recommends specific values for evacuation speed vs. glass cool down temperature.
    *** Extrapolated from a graph produced by Sherwood, Westinghouse Electric and Manufacturing Company.


    The first things you will notice in contrast to other temperature gauges are the various colored markings on the meter face. Each marking has a specific meaning and purpose. They are placed at these temperatures to reference the designated temperatures during various stages of the processing procedure. Once the processing technician is familiar with them the instrument will be invaluable in helping the technician to produce consistent, repeatable and reliable results, which will eliminate much of the guesswork from the processing procedure.

    Along the lower portion of the scale, the red lines at 150C and 200C are temperatures at which the manifold pressure and bombarding current should be adjusted, following the guidelines set forth in our discourse titled Recommended Bombarding Procedure. For the yellow, orange and red temperature ranges and corresponding numbers there is a legend in the lower left corner of the meter face with a short explanation of the various ranges: 1- Minimum glass temperature; 2- Acceptable glass temperature; 3- Preferred glass temperature. Some of these temperatures are also points of pressure and current adjustment while processing. These are also covered in more detail in our Recommended Bombarding Procedure.

    In general, the yellow temperature range between 225C and 250C should be considered a bare minimum, marginal glass temperature. The orange temperature range between 250C and 275C is a satisfactory glass temperature provided a fast pumping system is used and reasonable lengths of tubing are being processed. The red temperature range between 275C and 300C is the preferred glass temperature range for thorough processing. The red temperature range will release more impurities and contaminants from the interior surface of the glass and will allow a longer evacuation period before the glass cools to the re-absorption temperature of 175C.

    Along the upper portion of the scale you will notice three blue lines with symbols above them along with corresponding blue text in the upper right corner and lower right corner. The text in the upper right corner signifies that the blue lines and symbols to the left are for reference during the evacuation stage. These numbers are to be compared to the readings on a high vacuum gauge (ultimate vacuum gauge, micron gauge, etc.) to ensure that the tube is being evacuated at a sufficient rate of speed. The blue text in the lower right corner indicates that these are the Recommended Maximum (worst) vacuum gauge readings that should be obtained during glass cool down. Better vacuum levels should be strived for. The symbol < means less than and the symbol means microns (a vacuum measurement, which is the same as mTorr or millitorr). So, the symbol <10 directly above the 200C mark means less than 10 microns.

    For example: After the unit has been bombarded to the proper glass temperature the bombarder is turned off. The main stopcock is fully opened to evacuate the tube. The high vacuum gauge is turned on and the stopcock for it is opened. The tube begins to cool as indicated by the temperature gauge. When the needle on the temperature gauge drops to 200C the level of vacuum as indicated by the vacuum gauge should be <10 (less than 10 microns). When the glass has cooled to 175C the level of vacuum indicated by the vacuum gauge should be <5 (less than 5 microns), etc. If these marginal vacuum levels cannot be obtained, then the vacuum system does not evacuate quickly enough and quality units will be impossible to produce.


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    Copyright 2006
    Silica Vacuum Products