C-mac® module type RP81 is used for load monitoring of 3-phase motors, as the phase angle (cos _) between motor current and -voltage changes in proportion to the mechanical load of the motor.
You will see the biggest change in phase angle, if the motor is loaded between 0 and 60% of nominal load, which makes the RP81 suitable for monitoring of V-belts, pumps running dry, etc. (see page 6-6).
RP81 can be connected directly to motors with nominal current up to 6 A. If the current is bigger, you use a standard current transformer.
The unit is supplied with an adjustable start-up delay, which keeps the output relay activated independant of the power consumption, when the motor is starting.
By connection of pins 7 and 2 you can select if the relay releases at over- or underload.