I mean by simple device the simple , low cost , easy to use  instrument / arrangement to  measure  vibrations 

Abdelkadir Belhadj , Mohamadreza Beygifard, Ali Chaibakhsh,Juan David Berrio and Julio Mendez   ,  Many thanks for your answers for sure these answers will help  , Good Luck 

What do you mean by simple device?

the siempliest device i can think of are microphones, but you have to know the acustic response of the turbine working properly.

you can use vibration analyzers from SCHENCK Co.

For industrial applications, they are very well-known.  

Sir what do you mean by simple devices. And what do you want to measure ?

There is no simple devices, unless you want to measure the vibration of  rotating machine prototype by using some vibration meter or stroboscope or you can use some sensors linked to a data acquisition system ( View Labview), in industrial scale you can use vibration analyzers ( Bently nevada, Adre, SCHENCK)

Good luck.

 I mean by simple device the simple , low cost , easy to use  instrument / arrangement to  measure  vibrations 

Abdelkadir Belhadj , Mohamadreza Beygifard, Ali Chaibakhsh,Juan David Berrio and Julio Mendez   ,  Many thanks for your answers for sure these answers will help  , Good Luck 

Tri axial or by axial vibration measure devices, there are a lot in the market, GE, BKV, Pruftecknick etc, cost may vary from 5000 to 50.000 (ADRE from GE). If you acoplate this Gas turbine to a generator you can use as well a Grid Wave Analyzer, to measure the armonics in the electrical output, the cost here is even less, but you need to build a transfer function algorythm to adress the electrical armonics waves with the vibration signature of the gas turbine, there are even cheaper solutions, but the prediction confident level may be is not suficient to detect failures before huge damages...

i recommend to used laser type vibrometer.

 Barhm Mohamad   laser  type a good solution ,thanks