Solenoid constant time

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:

 http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b732.pdf [/ code]

Thank you for your response.