• Home
  • Download PDF
  • Order CD-ROM
  • Order in Print
Thermistor Bridge
MECHANICAL-ROTATION FREQUENCY MEASUREMENT

Neets Module 16-Introduction to Test Equipment
Page Navigation
  35    36    37    38    39  40  41    42    43    44    45  
2-7 Figure 2-4.—Thermistor bridge. Before power is applied, R1 and R2 in view A of figure 2-4 are used to adjust the current through RT-2. When the resistance of RT-2 reaches the equivalent parallel resistance of R6 and RT1 (122.4 ohms), the bridge is balanced. Meter M-1 reads 0 at this time. The rf signal being measured is connected to the test set and applied via the calibrated attenuator to RT-2. This causes the temperature of RT-2 to increase, thus reducing its resistance. The bridge becomes unbalanced, causing meter M-1 to deflect an amount proportional to the decrease in resistance of RT-2. Meter M-1, because of the operation of RT-2, reads average power. Q-6.   As the dissipated power increases, what effect does this have on the resistance of a thermistor? If the ambient temperature rises, the resistance of RT-1 decreases. This shunts more current around the bridge network and allows RT-2 to cool. The resistance of RT-3 decreases, maintaining meter sensitivity independent of temperature changes. Cavity Z-1 in view B of figure 2-4 is an ABSORPTION- TYPE FREQUENCY METER. This type of meter will be discussed later. FREQUENCY MEASUREMENTS Frequency measurements are an essential part of preventive and corrective maintenance for electric and electronic equipment. Some examples of the various frequency measurements follow: Rotation frequencies of some electro-mechanical devices, such as electric motors, must be determined.






Western Governors University

Privacy Statement
Press Release
Contact

© Copyright Integrated Publishing, Inc.. All Rights Reserved. Design by Strategico.