The SVP Bombarding A.C. Milliamperes Meter is a completely self contained unit with all electrical connections enclosed within a safe, PVC meter housing.

Unlike rectified meters, the SVP Bombarding A.C. Milliamperes Meter is based on a Simpson® True RMS Iron-Vane meter, which provides an accuracy of ± 2% deviation from the actual value @ 60 Hz. (See comparison) This eliminates the guesswork normally associated with using a lesser quality instrument (regardless of what suppliers sell them for) and assures the processing technician that the proper amount of current is being applied at the appropriate times throughout the processing procedure.
 

The large 4½” meter face allows the instrument to be mounted safely away from the operator while still providing at-a-glance information, and the 0-1,000 scale range is ideally suited for neon work where the maximum current applied is typically less than 1,000 mA for even the largest units. A 0-2,000 range meter of the same type is available by special order for shops involved in manufacturing large diameter, high current Cold Cathode Lamps.

SUMMARY:
A Bombarding A.C. Milliamperes Meter is one of the four instruments essential for proper luminous tube processing. This instrument monitors the level of bombarder current in milliamperes that is generated by the bombarder, through the tube being processed. It is necessary to accurately monitor the current for the tubing and electrode sizes used to ensure that the right amount is applied at the appropriate time. To do otherwise may cause damage to the electrodes, fluorescent coating inside the tube and adversely affect the glass structure. Therefore, it is desirable to use a True RMS Iron-Vane meter, which is considerably more accurate than a rectified meter.

Too high of a bombarding current during the first stages of processing may damage the phosphors in coated tubing, particularly in a moisture laden tube. This damage and loss of efficiency reduces the initial light output of the finished tube and may lead to premature discoloration and darkening in fluorescent tubing. High currents for extended time may create hot spots in the glass tube, particularly in tight bends. This may cause the glass to deform to some extent and induce adverse stress points within the glass structure. Excessive current will also damage the electrodes. “Sputtering” is usually the damage that is first noticed. Sputtering reduces the life of the electrode and therefore the tube and can cause discoloration near the electrode, both in clear glass and coated tubing. This situation is particularly troublesome in mercury tubes as the discoloration may spread for some distance into the tube. Further, the electrode wires where they attach to the back of the metal shell may become brittle causing the shell to fall off the wires. The damage and resulting tube failure may not be evident until the tube has been in service for some time.

Too low of a current can make the bombarding process take too long and not allow the glass and electrodes to reach the proper temperature. Although a slow “cook” time is more desirable than a fast one, if it takes too long the phosphors and electrodes may be damaged from extended exposure to high currents. While it is necessary to get the electrodes’ metal shells a bright, incandescent, light shade of orange (like an illuminated pumpkin orange) the entire length of the shell, only the minimum amount of current to accomplish this should be used and it should be accomplished in a reasonably short time. Therefore, bombarding current must be monitored accurately and the higher currents required to fully process the electrodes should only be used for a few seconds at the end of the bombarding procedure.