Screen equivalent circuit

The equivalent circuit of the various conductors and screening is shown in Figure 13.14. Where ... 

Next we proceed to the heater surrounded by the screen. Following the first four steps of Table 9.1, an equivalent electrical circuit is constructed as shown in Fig. 9.29(b). Note that the heater sees the ambient through the holes of screen and that the inner surface of the screen sees the ambient through these holes as well. The outer surface of the screen also sees the ambient. These facts respectively translate to the upper and lower branches of the circuit shown in Fig. 9.29(b). 

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