Techniques of Cathode Temperature Measurements as Applied to Commercial Cathode-Ray Tubes

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Abstract
Thermocouple, optical pyrometer, and retarding potential techniques for the measurement of cathode temperatures in commercial cathode-ray tubes have been investigated to determine their relative merits, limitations, and corrections. The thermocouple method is accurate and reliable provided necessary lead loss corrections are made. Application of this method to commercial tubes is limited by the expense involved. The optical pyrometer method is questionable when applied to an oxide-cathode coating due to considerable spread in spectral emissivity data; however, the method is reliable when applied to the cathode base nickel. The retarding potential method shows good correlation to the other methods and is directly applicable to commercial tubes with no modifications required. However, limitations are imposed by a number of factors, notably the stability of cathode emission and leakage current levels.