# How to derive a value from a transfer function

I have a scenario where a valve q_in(t) is pumping water into a tank of height h(t) and area A, which is then pumped out by a second valve q_out(t) that has a resistance to water flow R.

I got this transfer function:

$$\frac{H(s)}{Q_i(s)} = \frac{R}{A R s + 1}$$

Where R= 1.5m(m^3/min) and A= 2m^2

I would be grateful if someone could tell me how to get the value of Rs so I can plot the transfer function in Labview!

• Do you mean $\frac{H(s)}{Q_i(s)} = \frac{R}{A R s + 1}$? If so, please edit your question with the appropriate parentheses, or replace your relevant text-math with $\frac{H(s)}{Q_i(s)} = \frac{R}{A R s + 1}$. And you ask for the value of "Rs" -- do you mean "R times s", where s is the Heavyside operator? – TimWescott Oct 14 '19 at 16:43
• Yes sorry, R times s is what I want! I will change the equation now! – MelanieW403 Oct 14 '19 at 16:49
• Thanks for your help about the equation! – MelanieW403 Oct 14 '19 at 18:22
• If you could tell me how to get R times s so I could plot the values in a graph I would be very grateful. – MelanieW403 Oct 14 '19 at 18:24
• $s$ is an operator, not a variable per se. A transfer function is a shorthand for a differential equation that describes the behavior of a linear system. You can use a transfer function almost directly to get a frequency response of a system by substituting values into $s$, but to get a response to a signal in the time domain, you need to simulate the system, or solve the inverse Laplace transform of the output signal. This should be a matter of pushing the right buttons in Labview, but I'm not familiar with that program. – TimWescott Oct 14 '19 at 18:47