Abstract: An apparatus and method for monitoring the operation of centrifugal cyclones. Sensing means is disposed in the underflow spray discharge of a cyclone and is connected to electronic sensing circuitry adapted to produce a signal or alarm response when the cyclone ceases to operate in a normal manner. In one embodiment the apparatus and method employs a plurality of cyclones connected to receive feed material from a common manifolding means. Abnormal functioning of one cyclone of the group is immediately indicated by visual or audible alarm means and thereafter its sensing means may be disabled to permit the sensing circuitry to continue to be effective for the remaining cyclones. Delay means is incorporated in the circuitry to prevent a response when the abnormal condition is of short duration. One form of sensing means employs a probe which extends into the normal underflow discharge spray. Another form employs a paddle and switch assembly, with the paddle extending into the normal discharge spray.