Hello dougy83 and ericgibbs
Thanks for your responses. Here I have a DC input voltage. Please see the attached
View attachment 75812
I know if we have a variable resistor (case (a)), the response would be the same as (a). but I am wondering in what case I would have a response like case (b) maybe having just variable capacitor or both variable capacitor and resistor. I want to find response time and Vp. But as ericgibbs said maybe the variable capacitor has no effect in the response.
thanks in advance for your responses.
Morteza
Hello,
To get the response as in (b) you would turn the pot up high, then apply voltage, then turn the pot down and then back high again. That would give a time limited blip.
To get the blib using the capacitor, you could rely on the charging to get the upper bound, then turn the pot down to get the lower voltage again. This assumes R3 is smaller than R2. If R3 is too big the cap wont do much.
To find out the exact response you have to specify what you want the function of R2 to be. Some examples are:
R2(t)=t*R where R2=0 at time t=0 and at time t=t1 the resistance is R2=t1*R and this assumes a time limit.
R2(t)=t*R+K, where it's the same as above except there is some minimum resistance K.
R2(t)=R*(1-e^(-a*t)), where a is the controlling factor and R the scaling factor, making the resistance go up until a certain time then it tapers off.
R2(t)=Ra*t^3+Rb*t^2+Rc*t+Rd, where the various R's are the constants in the curve of the resistance R2.
R2(t)=R*(1-sin(w*t))/2, where R is the scaling resistance and w is the angular frequency of the change of resistance
R2(t)=R*sin(w*t), where R is again the scaling resistance and w the same as before but we allow R2 to become a negative resistance for a time.
So you see there are many possibilities. If we had the choice of what to make R2(t) to get a blip we would have a bunch of functions we could choose from. For a given form that is well specified we then turn this problem into a curve fitting problem.
Here's a simple example where the function used was R2(t)=K-t*R and running the experiment from 0 to some end time where R=Rmin. The applied DC voltage was 10 volts.