The following op-amp circuit is used to measure the changes of temperature in a system (Figure 2.20). The output voltage is given by

v_o(t) = ˆ’R(t)v_i(t)

Suppose that the temperature in the system changes cyclically after t = 0, so that

R(t) = [1 + 0.5 cos(20Ï€ t)]u(t).

Let the input be v_i(t) = 1 volt.

(a) Assuming that the switch closes at t₀ = 0 sec., use MATLAB to plot the output voltage v_o(t) for 0 ‰¤ t ‰¤ 0.2 sec. in time intervals of 0.01 sec.

(b) If the switch closes at t₀ = 50 msec., plot the output voltage v_o1(t) for 0 ‰¤ t ‰¤ 0.2 sec. in time-intervals of 0.01 sec.

(c) Use the above results to determine if this system is time invariant. Explain.

Figure 2.20:

Transcribed Image Text:

Thermistor R(t) to Ω ww vo(t) v:(t)