# Time Constant

1. Oct 25, 2006

### the_d

The problem is for a first-order instrument exposed to a step change of 100 units. If after 1.2 seconds the instrument indicated 80 units, estimate the instrument time constant.

the problem im having is chosen the correct formula for the time constant, any suggestions?

2. Oct 25, 2006

### SGT

The formula is
$$x(t) = A(1 - e^{-t/T})$$
where
• x(t) is the value at time t
• A is the final value
• T is the time constant

3. Oct 25, 2006

### SGT

I don't know why my LaTex formula didn't work. Here it goes in text form:
x(t) = A(1 - exp(-t/T))

4. Oct 25, 2006

much thanks