| 摘要 |
A known power test meter system, employing a self-adjusting impedance bridge comprises a first branch having one or more thermistors and a second branch having a selectively switchable 200 OMEGA /100 OMEGA resistance. The test meter system is used to calculate a so-called Voltage Reflection Coefficient (VRC) of a reference oscillator of a device under test. The VRC of the reference oscillator is used, in combination with the knowledge of a VRC of the test meter system to calculate power transfer between the reference oscillator and the test meter system, and ultimately to verify the output impedance of the reference oscillator. However, the temperature of the thermistor(s), in a sensor designed to operate at a 200 OMEGA resistance, can rise above a predetermined temperature when the 100 OMEGA resistance is in-circuit, resulting in inaccurate operation of, or even damage to, the thermistor(s). By using different resistances, advantage can be taken of the negative temperature coefficient of one or more thermistors (204, 206), resulting in temperature of the thermistor(s) (204, 206) operating within acceptable temperature limits. <IMAGE>
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