DE3007929C2 - Contactless controllable proximity switch - Google Patents

Description

3 4

output signal of the proximity switch is immediately clear. Base of transistor 73 connected to the flip-flop circuit, that there must be a malfunction resulting from Si The emitter of this transistor 73, which is used as npn trans-safety reasons an interruption in operation and interference suppression is formed on the one hand via the resistor

makes speaking repairs necessary R 4 with the connection 6 and on the other hand via the Wi-

According to the invention, the proper function 5 resistance R 5 with the connection 4 dss proximity switch

of the proximity switch both when connected from the outside. The collector of transistor 73 is

Check the damped oscillator as well as when the oscillator is not damped from the outside via the resistor R 7 to the base of the transistor, so that all are connected to the protection 74. The base of the transistor Γ4 is also

of the machines, the workpieces and the operator via the resistor R 6 with the connection 4

personnel to be observed safety criteria over- io bound, while the emitter of the transistor 7'4 immediately

can be checked. directly connected to terminal 4 is the collector

Advantageous embodiments of the proximity switch of the transistor 74 is via the resistor A 8 with the

ters according to the invention are the subject of the base of the transistor 73 and across the resistor λ9

address. connected to the connection 6 and forms an

The invention is explained below with reference to drawing 15 conclusion 5, which shows the actual output of the Kippschal-

nings explained in more detail It shows the direction and thus the entire proximity switch.

F i g. 1 shows a sound image of a preferred embodiment. Between the connections 5 and 6 can be

in the form of a proximity switch that can be used as an opener, evaluation and switching devices are

according to the invention, and inferred that in FIG. 1 dashed by a

F i g. 2 a circuit diagram of a preferred embodiment relay Re 1 is indicated,

form of a proximity switch that can be used as a normally open contact.

ters according to the invention. type, the probe coil L is normally

In detail, the circuit diagram according to FIG. 1, if se in a pot core open to the front, so that one disregards the circuit points 1, 3 and 7 initially built up from the circuit elements between magnetic field with great control, a QbIi- 25 can become. If you move a metal into this field, a proximity switch that can be used as an opener, then induced eddy currents flow in it, the pnp output transistor. This proximity switch removes energy from the field. These eddy current losses have a probe coil L on the input side, which usually lead to a deterioration in the quality of the resonant circuit, in a forward direction - ie in the direction of the so that the oscillation amplitude is reduced; the movable parts - open cup core is arranged 30 resonant circuit is damped in other words. The external terminals 2,3 of the feeler are mii If the resonant circuit and the oscillator oscillates, terminals 4 and 6 of the proximity switch users, then form .the elements R.2, \ t £ j 'R'x and L 1 is where a positive (+) or (via Al, Tl). a negative (-) voltage for the duration of the negative half-cell of the oscillation is applied parallel to the key voltage divider. This produces at the collector of the head coil L is a capacitor Cl, which together 35 transistor 72, a relatively 'high negative men with the feeler coil L a resonant circuit L, CX voltage because the resistance R 2 with the übribildet. gen elements of the voltage divider is high resistance.

The oscillator of the proximity switch according to Fig. 1 This has the consequence that the capacitor C2 at the input

also has two transistors T1 and 7 "2 and three gear of the flip-flop is charged. When the

Resistors Rx, Rx ', R 1 and R 2. The base to 40 transistor 72 then during the positive half cycle

The shorts of the transistors 71 and 72 are blocked by the oscillation, then the capacitor discharges

Resistance R \ with connection 6 of the proximity gate C2 slightly above resistance / 72 to the

switch connected. The emitter of transistor 71 is the next negative .Half-wave of the oscillation occurs,

on the one hand with the outer connection 2 of the probe head- The capacitor C2 smooths the voltage at the KoI-

coil L and on the other hand with the capacitor C 1 sensor of the transistor 72 or at the input of the flip-flop

bound. The collector of the transistor 71 is not connected in such a way that a direct voltage with connected

switches so that only the base-emitter path of the negligible residual ripple results in this voltage

Transistor 71 acts as a diode, but the- is so high that transistors 73 and 74 are conductive

These diodes are specially controlled in their electrical properties, so that the relay between the terminals

precisely on the properties of the transistor 72, 5 and 6 attracts

If the resonant circuit, as described above, stood R 2 is connected to terminal 6 and its attenuated by a metal part, then the oscillating emitter is amplitude amplitude via resistor Rx to terminal 1 of the oscillator is smaller, then that of the proximity switch is connected, ie charged more with a capacitor C2 , while the span tapping of the probe coil L, which is connected to the collector of the transistor 72 opposite the tapping in two partial windings L 1 and L 2 divides voltage at terminal 4 becomes smaller and smaller until it becomes. Eventually it is no longer sufficient to turn transistor 73

With the oscillator described above, one can be controlled in a conductive manner. The transistor 73 then blocks

Flip-flop connected, which has a capacitor, the transistor 74 and the relay Re 1 drops. at

C 2, resistors R 3 - R 9 and two more transistors - the considered proximity switch is the resistor,

ren 73 and 74, the capacitor C2 serving for the setting ί ?? κ Ansnrechahstjindes ie

is also to be regarded as part of the oscillator. that distance, except for a metal part to the

The condensate front of the probe head must be brought up from the components mentioned,

gate C 2 on the one hand to connection 4 of the proximity scarf the oscillator vibration for tilting the tilting

ters and on the other hand to the collector of the transistor 65 circuit to be sufficiently vaporized, in two partial resistances

72 connected. The common connection point would be divided into Rx and R'x, which are connected in series,

of the transistor 72 of the resistor R 2 and the con- On the purpose of this measure is further below

capacitors C 2 is discussed in more detail with the via a resistor A3.

If such a proximity switch is used to monitor the operating conditions on a machine, a malfunction of the proximity switch can have disastrous consequences. In general, it is not critical if, due to a malfunction, an attenuation is falsely simulated and the relay Re 1 drops out. In this case, an operating state is (incorrectly) displayed which prevents the machine from being switched on. However, if the oscillator is actually damped, for example because a machine part has soon reached its end position, but the output signal of the proximity switch still simulates a free oscillation of the oscillator, which is the case, for example, if one of the transistors Γ2, T3 ts or Γ 4 breaks down then the machine can start up anyway, possibly resulting in serious property damage or even personal injury. For this reason, it should be possible to check the functionality of the proximity switch.

This test option can be used with a proximity switch according to FIG. 1 can be created by tapping the probe coil L, ie connection 1, via the dashed line V directly connected to connection 1 'which is connected directly to a connection 7 of the proximity switch or less long line that is connected to the connections 4 and 7 of the proximity switch provides a button K then you can short-circuit the winding part L 1 of the probe coil L by closing the button. This dampens or suppresses the oscillation of the resonant circuit or the oscillator so that the relay drops out at Re 1 if the proximity switch is working properly, but has to pull again after opening the pushbutton contact. The test switch shown in FIG. For the sake of simplicity, any suitable switch, in particular an electronic switch, which can be periodically closed depending on the particularities of the system in question, in order to check the function of the proximity switch or in each case before the initiation of corresponding machine functions, is shown as button K for the sake of simplicity.

In the above-described, particularly simple variant of the invention, in which hardly any significant additional effort is required, difficulties can arise under certain circumstances if a longer cable is present between the test switch and the connections 4 and 7 of the proximity switch Capacities of the cable can namely prevent an effective short circuit of the winding part L 1. In addition, the cable acts like an antenna, through which all possible malfunctions in the proximity switch can take effect when the test switch is open. In addition, the leads to the connections 5 and 7, which are usually just as long, form a line with distributed inductances and capacitances, so that switching edges from the output of the flip-flop lead to a feedback to the eo input of the proximity switch, so that it is faster in a transition area Can turn the sequence on and off. The circuit variant explained above should therefore only be used with relatively short connecting cables up to a length of about 2 m. In this case, too, it may still be necessary to insert a small series resistance in the short circuit.

If the function test is to be at least largely independent of the length of the connecting cable, then it is advantageous if instead of the short-circuit connection between the connections 1, 1 'and 3, a transistor circuit consisting of a transistor 7 "5, resistors R 10 and RW and a capacitor CZ is provided In this circuit variant, the collector-emitter path of the transistor T5 is between the terminals 1 and 3. The base of the transistor 7 * 5 is also connected to the terminal 3 via the resistor 10 and via the resistor R 11 to the terminal Γ. in this case, the resistor R 10 provides the important especially at higher temperatures low-resistance connection between emitter and base, while the resistance RW serves to limit the base current Finally, the capacitor Ci is used between the terminals Γ and 3 as a filter member for blocking interference voltage peaks that can arrive via the connecting cable.With the aid of the capacitor C3, w Furthermore, the feedback of interference voltage pulses due to output pulses from the multivibrator to the input of the proximity switch is suppressed

In the circuit variant under consideration, the transistor T5 is turned on when the test button K 1 is closed, so that the winding part L 1 can be short-circuited via the switching path of this transistor. In an embodiment of the invention, however, there is also the possibility of inserting a resistor R 12 in the collector branch of the transistor 7 * 5, which is dimensioned so that the damping of the resonant circuit or the oscillator is about the same as the damping by a metal part, in which by the resistors Rx, R'x set response distance. If the relay Re \ drops out when the test switch Ki is closed and picks up again when it opens, then it is not only ensured that the oscillator of the proximity switch can be dampened at all, but also that the response distance has not become too small, which could lead to the oscillator of the proximity switch continues to oscillate although the metal part to be monitored has come close enough

In the case of the circuit under consideration, the resistance for setting the response distance is, as mentioned above, divided into two partial resistances Rx and R'x , which are connected in series, the switching path of a transistor 76 being connected in parallel with the partial resistance R'x The transistor T6 is connected via a resistor R 13 to its collector and to the connection point of the partial resistor R'x and the emitter of the transistor T2 . In addition, the base of the transistor 7 * 6 is connected to a connection 8 of the proximity switch, which is connected to the connection 4 of the proximity switch via a test button K 2 with break contact. The connections 4 and 8 of the proximity switch can be connected to the connections of the test button K 2 be connected via a cable of the appropriate length.

If the oscillator of the proximity switch is damped by a metal part to be monitored, which is accordingly located close in front of the probe, then the transistor 7 * 6 can be switched on by pressing the test button K 2 , whereby the partial resistance R'x is bridged. As a result, the resistance value of the resistance combination Rx, R'x, which determines the response distance, is reduced in such a way that the oscillator operates properly

Function of the proximity switch would have to swing again. If this is not the case, then this means that the response distance has decreased compared to the originally set response distance or that the metal part has been brought closer to the probe than was intended when the system was set. In both cases, a check of the system is necessary, which is indicated by the fact that the oscillator does not start to oscillate again despite the fact that the partial resistance R'x has been bridged.

From the above explanation of the function of the circuit according to FIG. 1 it becomes clear that the test of whether the oscillator of the proximity switch can be steamed at all can be carried out with the circuit components R'x, 7 * 6, R 13 and K 2 described, namely if the transistor Γ6 is normally in the conductive state holds and then blocks it for testing purposes, with the additional effect of the partial resistance R'x with appropriate dimensioning and proper functioning of the proximity switch, a damping of the oscillations of the oscillator would have to occur. But it is also clear that, in a modification of the function of the circuit, the resistor R 12 could be dimensioned so that the oscillator would vibrate with conductive transistors 7 * 5 and would be damped when a metal part approached the probe. If the damping caused by the short-circuit branch with the resistor R 12 when the transistor Γ5 was conducting would then be canceled by blocking the transistor 7 * 5, the oscillator could start to oscillate again, although its resonant circuit is damped from the outside by a metal part. The functionality of the proximity switch can also be checked in this way.

F i g. 2 of the drawing shows a proximity switch which can be used as a normally open contact and has a flip-flop circuit, the output transistor 7'4 of which is an npn transistor. The circuit according to FIG. 3 works completely analogously to the circuit according to FIG. 2, with the only difference that the conductivity type of the transistors 7 * 3 and 7 * 4 is reversed, and that the relay Re 1 at the connections 4 and 5 of the proximity switch consequently picks up when the oscillator is sufficiently attenuated and drops out when the Oscillator oscillates freely

With the proximity switch according to FIG. 1 all errors that occur in the circuit and in the probe head can be eliminated can recognize perfectly. In particular, the following errors are reliably detected, even when the Proximity switches could simulate a vibration:

The switch variant readily results, particularly advantageously, in that the errors are detected in each case that can really lead to a serious malfunction or an accident. While

namely with the opener variant the short circuits already are detected in the switch itself, cold soldering points or cracks can be found in one with the closer version the carrier carrying the components and connecting lines, in particular a thick-film substrate, is recognized which incorrectly lead to vibrations there.

For this purpose 2 sheets of drawings

1. Capacitor C 2 is broken down (short circuit);

2. Collector-emitter path of transistor 7 * 2 is broken down;

3. the resistance value of the resistor Rx or the partial resistances Rx, R'x has fallen below the target value (for example, if one of the resistors is charred);

4. the collector-emitter path of the output transistor 7 * 4 broke through;

5. the collector-emitter path of the input transistor 7 * 3 has hit through.

It is like comparing the openers Switch variant with the one used as a normally open contact

Claims (8)

p9f »ntancnrii / <hP · The grounding relates to a contactless, controllable claim. fen proximity switch for monitoring movable 1. Contactless controllable proximity switch parts with an oscillator with one in its impedance for monitoring moving parts with an Os- inductive variable that is variable due to the approach of the parts zillator with one in its impedance by proximity s or capacitive control element and with one to test the parts variable inductive or electrically switchable damping circuit for purposes of capacitance, zitiven control and a too Prflfzwek- through which, in its de-activated from the outside oscillator ken electrically switchable damping circuit, can be brought about by such damping that the which, when the oscillator is not damped from the outside, an oscillator oscillation is interrupted. such attenuation of the same can be brought about that io Such a proximity switch is from DE-OS the oscillator oscillation is interrupted, since 21 07 145 known With this known approximation characterized by the fact that the control switch provides the option of activating the function of the control circuit (TS, R 10 to R 12, K 1; T6, R 13, Rx, R'x, circuit to be checked by ensuring that a targeted K 2) designed in such a way that when the oscillator designed as a breakaway oscillator is damped from the outside, damped oscillator such undamping des- is by means of an electrically switchable damping same can be brought about that the oscillator is brought about again fungskreises to determine whether if the oscillator starts to oscillate, it can be steamed at all, with 2. Proximity switch according to claim 1 with a tearing off the vibrations by damping the response distance-determining resistance, the oscillator is brought about, which is a jump signal characterized in that the damping circuit 20 has the result, the occurrence of a flawless Funkderart is formed that the effective resistance signaling the proximity switch,
Based on this prior art, the resistor (Rx, R'x) is based on the object of specifying an improved damping circuit IT6, R 13, R'x, K 2) which can be lowered by proximity switches , in which even with 3. Proximity switch according to claim 2, characterized by 25 damper oscillator input stage for characterized in that the response distance loading a check of the correct operation of the matching resistor in two partial resistors (Rx, circuit is given R'x) of which one (R'x) is subdivided by beta. maintenance of a test switch (K 2) can be short-circuited, production switch according to the invention is thereby achieved 4. Proximity switch according to claim 3, characterized in that the damping circuit is designed in such a way that the short-circuitable Teilwi- with externally steamed oscillator such Entderstand (R'x) the collector-emitter path of a damping of the same can be brought about Oszilla switching transistor (TS) is connected in parallel whose gate starts to oscillate again Base voltage by actuating the test switch The decisive advantage of the (K 2) is controllable 35 The design of the proximity switch consists in 5. Proximity switch according to one of claims 1 that first of all there is the possibility of Entbis 4, characterized in that the damping of the oscillator is to be simulated when a Befungskreis (T5, R 10 to R 12, K 1; Γ6, R 13, Rx, R'x, damping by a movable part to be monitored K 2) can be actuated periodically. is present If this, carried out for testing purposes, 6. Proximity switch according to one of claims 1 40 mulated undamping then not to a corresponding 5, with an inductive, one with a tap corresponding output signal of the proximity switch, provided probe coil containing probe head is immediately clear that there is a malfunction of the oscillator's oscillator, thereby marked, which for safety reasons an operational interruption that a winding part (L 1) 45 lying between the tap and one of the connection and corresponding repairs required external connections makes. In practice, such a check of both probe coils (L) can be carried out by a series connection of a defined counter which is connected in parallel, for example periodically or before each machine command, which moves the position to be overcome (R 12) and the collector-emitter path triggers the relevant parts nes test transistor (TS) can be bridged, whose design according to the invention of the proximity base voltage via a test switch (φ switchable 50 switching switch enables the correct response distance to be checked by simulating a 7. Proximity switch according to claim 6, characterized corresponding ner the response distance Bedämpgekennzeichnet, that the collector of Prüftransi- evaporation of the mechanically undamped oscillator in stors (T5) with the tap of the feeler coil (L) that case, upon generation of the test signal not connected is that the emitter of the test transistor 55 is allowed to oscillate, and through a defined damping (TS) with an external connection (3) connected to the one pole (+) of a supply of the oscillator mechanically damped from the outside, the voltage source in this case for the Duration of the test signal is again connected to the probe coil (L) , so that the base must oscillate, since the undamping of the operating condition of the test transistor (TS) via the test switch (K, sets conditions that create a response K 1) and a current limiting resistor (R 11 ) 60 stand, which is smaller than that for safety with the other pole (-) of the Speisesnanniingsnijplie are still permissible sige approach to be überaverbindbar, and that between base and emitter corresponding movable file. of the test transistor (TS) a bleeder resistor (R 10) In addition, there is still the possibility of is provided. the oscillator that is not steamed on the outside causes damping 8. Proximity switch according to claim 7, characterized in that 65 of the oscillator simulate the damping caused by characterized in that the base of the test transistor corresponds to a movable part to be monitored. fT5) a filter element (C3) is connected upstream. If this was carried out for testing purposes, simulated Attenuation then does not lead to a corresponding