Patent GB-1480848-A (GB)
Title: Bearing wear detection devices
IPC: G01M13/04
Filed: 1974-10-01
Abstract: 1480848 Detecting bearing wear electrically APV CO Ltd 1 Oct 1974 [8 Oct 1973] 41248/74 Heading G1N Wear in bearings in rotary machines is detected by mounting a magnet on one of the rotating parts and a coil on another such that when the parts rotate eccentrically a voltage is induced in the coil. In the embodiment of Fig. 7 shaft 3 of a motor driving a pump impeller is provided with an extension journal at one end in which are mounted two groups of three permanent magnets 1 and associated polepieces 1a, with one group on each side of the shaft 3 facing opposing directions, Fig. 8 (not shown). An extension of the motor stator has a coil 2 wound thereon, surrounded by soft magnetic circuit 8, 9, and a centre polepiece 11  integrally mounted with the stator extends into a drilling of the journal extension. As long as the journal rotates coaxially with the stator the magnetic flux from each magnet 1 is divided in a constant proportion between polepiece 11 and the magnetic circuit 8, 9 and no significant voltage is obtained from coil 2. However if the journal is not coaxial and the distances between polepieces 1a and components 8, 9 varies an alternating voltage is obtained from coil 2 whose amplitude is proportional to eccentricity. The signals from the coil 2 may be monitored by a meter or applied to a differential amplifier which compares the peak value with a set value and charges a capacitor whenever it exceeds the set value. If this is exceeded on a sufficient number of successive revolutions the charge on the capacitor switches on a transistor to energize a cut-out relay for the motor. The circuit being such as to keep the relay energized once the eccentricity has been exceeded, Fig. 10 (not shown). The circuit of Fig. 11 enables the greatest output from the coil to be memorized. Amplifier A2 switches when the eccentricity signal picked up by coil 2 and developed across resistor Rl exceeds a reference voltage generated across resistor R2 by a transistor T 1 . When this occurs on a predetermined number of cycles determined by pump circuit C1, C2 and associated diodes F.E.T. T3 switches to generate via transistor T2 a clockpulse for counter ICC. The four binary outputs of the counter are connected via resistors R4 to R7 to transistor T 1  so that as the count increases by one the base current of transistor T 1  increases to increase the reference voltage across resistor R2. An indication of bearing wear may be obtained from across R 3  and if a cut-out is required to operate at a given value of wear the counter outputs are linked to AND gate 41 provided with two floating inputs. As shown the AND gate 41 conducts at a counter output of 12 and OR gate 42 is energized to switch transistor T4 to energize cut-out relay 43. OR gate 46 detects when there is no voltage from coil 2 indicative of the sensing circuit being disconnected and energizes the cut-out relay. Transducer arrangements: Figs. 1 to 6 (not shown). A single permanent magnet may be mounted on the shaft and a pick-up coil on the stator or a soft magnetic polepiece may be mounted on the shaft which is energized by a D.C. coil mounted with the pick-up coil on the stator. Alternatively the magnet or polepiece may be mounted on a hollow shaft with the pick-up coil and energizing coil mounted on the stator which lies inside the shaft. A group of magnets may be mounted on a hollow shaft in the inside of which is a magnetic polepiece the pick-up coil being mounted outside or inside the shaft.