ELECTRONIC AUXILIARY CONTACT FOR A CONTACTOR

Abstract: The present invention relates to an electronic auxiliary contact for a contactor, said auxiliary contact comprising at least one switch element (6) controllable to the ON and OFF states for the purpose of indicating the position of the contact bridging member in said contactor (2), and a switch-activating element (3) mechanically connected to said contact bridging member and capable of activating said switch element (6). According to the invention, said switch-activating element (3) incorporates at least one activating element (7, 9), and said switch-activating element (3) makes no mechanical contact with said switch element (6). The system according to the invention provides a reliable method of monitoring the operation of a contactor.

Description: Electronic auxiliary contact for a contactor The present invention relates to an electronic auxiliary contact for electromechanical contactor in accordance with the preamble of claim 1. Conventional contactors employ mechanical auxiliary contacts according to Fi to accomplish different kinds of control and monitoring signals. The contact bl is constructed with the help of a moving contact element a attached to the cont bridging member, said element carrying a portion of the circuit b of the auxili contact, said portion opening and closing the circuit c when said contact elem is in either of its home positions. The contacts are sprung to attain longer me anical life. A mechanical contact is suitable for controls performed at conventional mai voltage levels, but developments in automation technology have set new deman on the quality of control and monitoring signals. Low voltage level and small c rent as well as precise timing of the signals are now desirable. Information on t position of a contactor's contact bridging member, for instance, can be signall by means of mechanical auxiliary contacts, but this prior-art technique involv problems that compromise the reliability of obtained information: Bouncing contacts at the opening and closing generates signal transients which cause jitt in the precise tuning of events, and due to the mechanical play of contacts, t timing of the obtained signal has insufficient accuracy for positional monitoring the contact bridging member. Moreover, contamination and oxidation of cont surfaces cause malfunctions, particularly at low current and voltage levels. It is an object of the present invention to overcome the above-described disadva tages and to achieve a novel system for obtaining and utilizing information on t positions of a contactor. The system according to the present invention is based on the idea that the act ating element of the auxiliary contact operates without mechanically contacti the actual switch body of the auxiliary contact More specifically, the auxiliary contact according to the invention is characterize by what is stated in the characterizing part of claim 1. An electronic auxiliary contact according to the invention offers substantial bene fits with respect to the conventional technology. Thus, a stable signal is obtaine from the position of the contact bridging member, contact bouncing transients ar avoided and the timing precision of the positional information is jitter-free. Due to the hermetic protection of the switch element, the characteristics of the auxili¬ ary contact are not deteriorated by contamination or oxidation. The electroni auxiliary contact has no moving parts thus retaining a constant timing precision o the positional information even in extended use, and isolation problems are relieved by the mechanically noncontacting nature of the auxiliary contact switc circuit in respect to the moving parts. The electronic auxiliary contact can provide reliable positional information for process control computer also from a circuit operating at a low supply voltage. The position of the contactor's contact bridging member can be determined wit an extremely high precision. The electronic auxiliary contact has a simple con struction, and by integrating more electronics to it, possibilities of multiple differ ent monitoring function are feasible not ever attainable at a sufficient accuracy b means of a mechanically operating auxiliary contact A single auxiliary contac block can incorporate one or more position sensors, thus making it possible t detect various intermediate positions complementing the conventionally indicate home positions. The invention is next examined in detail with the help of the attached drawing and exemplifying embodiments illustrated therein. Figure 1 shows a conventional auxiliary contact in a side view. Figure 2 shows a perpective view of an auxiliary contact according to the inven tion attached to a contactor. Figure 3 shows a sectional view of an embodiment of the auxiliary contact acc ing to the invention illustrated in Fig. 2. Figure 4 shows an alternative embodiment of an auxiliary contact according to invention in a perspective view. Figure 5 shows a block diagram of the signal processing block of an auxili contact according to the invention. According to Fig. 2, the contactor's auxihary contact block 1 is fastened to body 2 of the contactor. According to Fig. 3, the auxiliary contact block is co prised of a two-part body block 4 and an oblong shder 3, which is situated ins the body block 4 and is guidedly movable along a groove 5. The slider 3 incorp ates a peg 8 aligned to one end of the shder perpendicularly to the longitudi axis of the slider. The peg 8 is oriented toward the. inner side of the contactor Thus, the auxihary contact block 1 is fastened by fitting the peg 8 of the shde to the contact bridging member (not shown) of the contactor 2. The shder 3 moved along the groove 5 exactly by the same distance as the contact bridgi member of the contactor 2 moves between its upper and lower home positio The position of the slider 3 is detected by sensors 6 and 6' which are permanen mounted to the body block 4 of the auxiliary contact block 1, whereby said se sors in the described embodiment are Hall sensors. Alternatively, the sensors c be replaced by inductive or capacitive proximity sensors or optical gap senso Magnetically-activated switch contacts are also feasible as sensors, but they do offer as good precision as is attainable with the other sensor types describ above. One auxiliary contact block 1 requires two sensors 6 and 6'; one sens serving for the upper and one for the lower home position, respectively. The fu tions of a single-position mechanical auxihary contact can be accomphshed using single sensor alone. Fig. 3 illustrates a construction having two sensors 6 and 6', whereby said co struction is capable of replacing a dual-function mechanically switched conta The sensors 6 and 6' are placed on the upper surface of the slider 3. Because t sensors 6 and 6' are of the Hall sensor type, a small permanent magnet 7 is fas tened to the shder 3, whereby the motion of the magnet to coincide with the sen sor 6 or 6' sets the respective sensor to the ON state. This arrangement makes i possible to adjust the effective stroke of the slider and the activation positions o the sensors by varying the size of the magnet 7 and the mutual distance of th Hall sensors 6 and 6\ Because the Hall sensors 6 and 6' will only be activated b a magnetic flux aligned perpendicular to their measuring surface, it is possible t select a suitable sensor/magnet combination and align these elements appropriate ly with respect to the flux emitted by the main magnetic circuit of the contactor so that an extremely accurate sensor function, free from interference by stra fields, is achieved. The signals from the sensors 6 and 6' are taken in a cable 35 t a signal processing unit to be described below; thus, an embodiment based o Hall sensors requires a cable with three separate conductors, one for each Hal sensor element. In practice the number of conductors is increased to the qty. o sensors plus two, because each sensor element needs a separate signal line com plemented with a common ground and supply voltage line. Therefore, the numbe of conductors necessary in the described embodiment is 4. Fig. 4 shows a corresponding construction suitable for inductive or capacitiv sensors 9. The mechanical basic construction herein is similar to that described fo the embodiment illustrated in Fig. 3, so two sensors 9 are also needed in thi embodiment This kind of sensors 9 can operate without an external magneti flux, because they sense the proximity of a metallic vane 10 in front of their sens ing surface. Therefore, the slider 3 is provided with small metal plates 10 whic are aligned with respect to the sensors 9 so that one plate is coincident with th upper position sensor when the contact bridging member is in its upper hom position and, correspondingly, the other plate is coincident with the lower positio sensor when the bridging member is in its lower home position. The mechanical design of the auxihary contact block can vary for different type of contactors, yet maintaining an identical principle of operation. An electronic auxiliary contact operates at a low supply voltage of 5...48 VD depending on the sensor type used. Hall sensors as well as inductive, cap and optical sensors require a separate supply voltage line and a dedicated line. Maximum allowable load current from the sensor output stages is limit a few tens of milliamperes at its best, so an electronic power driver stage or is necessary for controlling voltages or currents at higher levels. In most ap tions the operating environment tends to cause interference with the me ment, so the output signal from the sensor elements must be processed by tronic means in either the sensor block, its immediate vicinity or the autom system. An application of the electronic auxiliary contact is in contact bridging me position monitoring of contactors. The contactor's electronic auxihary co block having separate sensors for the upper and lower home position sensi connected to a logic circuit shown in Fig. 5. The logic circuit comprises inpu a lower-position sensor signal 30 and an upper-position sensor signal 31, inve Schmitt triggers 12 and 13, digital low-pass filters 14 and 15, and a posit information processing logic circuitry comprised of three NOR gates 16, 17 18, and one AND gate 19. The logic circuitry processes input signals taken t inputs 30 and 31 into four different state-indicating signals defined as: Signal sors disconnected" 20, signal "Contact bridge driven up" 21, signal "Contact b midway" 22 and signal "Contact bridge driven down" 23. In severe operating conditions the input signals will carry superimposed inte ence consisting of mains frequency harmonics or high-frequency transients ca by frequency converters and other switch-mode power sources. The Schmitt gers 12 and 13 at the logic inputs filter away low-amplitude interference fro input signals irrespective of their frequency. The filtration result will be the effective the wider the hysteresis of the Schmitt trigger 12 or 13. Further impr ment in filtration can be obtained by using a large input voltage swing. The in are taken high by pull-up resistors 32 and 33 for the purpose of sensing the i rity of sensor connections. At the second stage the interference components managing to pass the Sch triggers 12 and 13 are filtered away by one-bit digital filters 14 or 15. The filter 14, 15 can be a median-producing filter or a nonlinear low-pass filter that removes transients from the signal. The logic circuit described above for processing of positional information is imple¬ mented so that the output stage of a nonactivated sensor 6 is in the ON state, while the output stage of an activated sensor is in the OFF state. If neither of the sensors 6 is activated, that is, both of their output signals are taken low, the con¬ tact bridging member is interpreted to be in a midway position. Signal indicating this state is formed by the AND gate 19. A situation having both sensors 6 acti¬ vated is considered impossible, so its occurrence can be interpreted to indicate severed connection to the sensors. Signal indicating this state is formed by NOR gate 16. When Hall sensors are employed, their output signal properties must be considered in the placement of the sensors. Signals "Contact bridge driven up" and "Contact bridge driven down" are formed by NOR gates from the input sig¬ nals 30 and 31, complemented with the signal "Sensors disconnected" 20. Several auxiliary contact blocks 1 can be connected in parallel, which in larger contactors offers a possibility of detecting contact bridging member jamming slant- ingly that generally is indicative of contact welding. Information on contact bridg¬ ing member position can be employed even in a wider scale for controlling a contactor. For instance, the position state signals can be utilized to monitor contactor opening during hold and then to activate necessary functions to re-es¬ tablish contactor hold. Any of the discussed sensor types are suitable for use with the above-described circuitry provided that they incorporate an open-collector output stage capable of driving the logic circuitry sensor inputs to a logic zero state.

Claims: WHAT IS CLAIMED IS: 1. An electronic auxihary contact for a contactor, said auxiliary contact comprising - at least one switch element (6) controllable to ON and OFF states for the purpose of indicating the position of the contact bridging member in said contactor (2), and - a switch-activating element (3) mechanically connected to said con- tact bridging member and capable of activating said switch element (6), characterized in that - said switch-activating element (3) incorporates at least one activating element (7, 9), and - said switch-activating element (3) makes no mechanical contact with said switch element (6). 2. An auxihary contact as defined in claim 1, characterized in that said activating element (7) is a permanent magnet when said switch element (6) is a Hall sensor. 3. An auxihary contact as defined in claim 1, characterized in that said activating element (10) is a piece of material having a metallic character when said switch element (9) is an inductive sensor. 4. An auxihary contact as defind in any of foregoing claims, character- i z e d in that, for the purpose of processing the switch output signal triggered by said activating elements (7, 10), said auxihary contact (1) incorporates a signal- processing unit (12...33) for elimination of interference and processing of informa¬ tion related to the position of said contact bridging member of said contactor (2).

Inventors: KIISKINEN ESKO, RAJALA ERKKI, SOLANTI PETRI, KIISKINEN, ESKO, RAJALA, ERKKI, SOLANTI, PETRI
Applicants: ABB STROEMBERG KOJEET OY
Application year: 1991
Main classification: H01H50
IPC codes: H01H9, H01H50