# Frequency vs time constant

What happens when I have a low pass filter with R = 1kΩ C = 0.1 µF and I input a square signal with different frequencies? Will the time constant be the same for all frequencies?

τ = 100 µs for 1 kHz but when I increase the frequency τ starts to decrease on my oscilloscope. I thought τ was constant regardless of the frequency.

• What do you mean, "τ starts to decrease on my oscilloscope"? How can you tell? – Dave Tweed Nov 10 '18 at 22:06
• How do you measure $\tau$ on your scope? – Arsenal Nov 10 '18 at 22:06
• To calculate the time constant I do this: Delta C = C2-C1=487.67- (-481.99)=969.66 0.63(969.66)=610.88 610.88-487.67=123.21 the I placed C2 on approximately 123.21 and read dT which is 100us – guasabito Nov 10 '18 at 22:20