Hello, I have a small problem. Solenoid has a resistance of 14.2 ohms and an inductance 0.056H is connected in series with a resistance 2.2Ohm Thus calculated is the Tau = L / R = 0,056 / (14.2 + 2.2) = 0.0034s But the measured value is 0.02s The measurement is done on an oscilloscope for resistance. Source is a classic laboratory. If I measure only air-core coil corresponds to the time constant. How is it possible that tau is based on much more? Solenoid Type: Code (Text): http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b732.pdf [/ code] Thank you for your response.