Solenoid constant time

[JardaK]

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] http://docs-europe.electrocomponents.co ... 01b732.pdf [/ code]

Thank you for your response.