An emission controller for a thermally heated filament was designed and constructed, which was simple in construction using commercially available elements and parts, superior in stability, and versatile in the research of vacuum science. The design was simplified by using integrated circuits (IC's) and a photo-coupled isolator. The two most important facts that dominate the characteristics of the controller should be the stability of a zener diode that was used for a voltage reference and an overall frequency response of the system including a thermal characteristics of the filament. The range of the emission current was 0 to 10 mA. The stability measured was 0.35% for the change of a line voltage from 90 to 110 V, 0.01%/°C for the change of room temperature, and 0.1% with time after a warming up for only 30 seconds. Modifications for larger emission current and for better stability are also described.
View full abstract