P48SRR - Shaft Rotation   P48SMP- Shaft Rotation - Relay normally energised whilst detecting pulses.  If the pulses stop or fall outside the set time period the relay deenergies(P48SRR)/energises (P48SMP)
 

P48TR - Tachometer - The output relay energises when the rate of pulses from external contact/detector is greater than the trip level set on the unit (in r.p.m.) If the rate of pulses falls below the trip level, the relay will deenergise.