Which Sensors are Better for vibration measurement of Cooling Towers?

good answer by tariq fayaz well explanied.

General purpose sensor types AC102 (top exit) or AC104 (side exit) could be used for measuring vibration frequencies greater than 30 CPM (0.5 Hz).

Special purpose low frequency sensor types AC135 (top exit) and AC136 (side exit) could be used to measure vibration frequencies greater than 12 CPM (0.2 Hz)

Velocity transmitters are the best choice for cooling towers. We have installed CMS 2110 SKF which is  givening good results. Before selection proper engineering should be carry out like the place of intallation, base frequency determination.