Electronics
RC time constant
Resistance and capacitance against the time constant they set.
Readings
Drag the red line, or type into any two boxes — the third is solved. The marked box is the one being solved for.
Print at 100% scale, then check the 100 mm bar with a rule before trusting a reading.
Why this one is an instrument
Picking an RC pair is a search, not a sum. You have a time constant in mind and a drawer of preferred values, and you need the pair that lands nearest while keeping the resistor in a sensible range for the impedance around it. Sweeping the line along the τ scale shows every workable pair at once.
- Equation
- τ = R · C
- Constants
- R in kΩ, C in µF, τ in ms
- Ranges
- R 1–1000 kΩ · C 0.01–100 µF
- Reading
- Any two values fix the third. Outside the printed ranges the instrument stops being valid — that is what the end marks are for.
These are drawn from the stated equation and nothing else. Where an equation is itself an approximation — hyperfocal distance and tap drill sizes both are — the instrument inherits that approximation exactly, no better and no worse.