Introduction to instruments
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Bolometer mount:It consists of a thin mica disc. It consists sprayed silver electrodes. There are through silver plated holes which enables the contact of outer electrode with circular electrode on opposite side. Two depleted Wollatone wires of diameter equal to 1 micron are mounted between centre and outer electrode. These wires are very short and typically of length 1 - 2 mm. With normal bias power, for d.c. conditions, the resistance of both the wires is about 100 D. The holder is used to clamp the mica disc which makes contact of upper electrode with the metal case and other electrodes are insulated from co-axial line as shown in the Fig. The circuit is completed through the thin mica sheet which provides bypass capacitance. 
The measurement of unknown RF. power is done by using bolometer bridge in which a known A.F. power is superimposed on unknown RF. power. The schematic of power measurement using bolometer bridge is as shown in the Fig. 
Using the variable resistance R and the d.c. bias voltage Yss, the current is adjusted till bolometer element is heated and its resistance equals R1. With this value, bridge achieves balance condition. The test RF. input is switched off which again unbalances bridge. To achieve the balance condition again, the A.F. voltage is increased till RF. power equals 
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