CH682608A5 - Arrangement for monitoring of AC switches. - Google Patents

Description

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The invention relates to an arrangement for monitoring AC switches of the type mentioned in the preamble of claim 1.

Such arrangements are suitable, for example, for monitoring switches for actuators such as fuel valves and ventilation flaps.

Arrangements of the type mentioned in the preamble of claim 1 are known from DE-PS 3 044 047 C2 and from DE-PS 3 041 521 C2. In both of these arrangements, a microprocessor is programmed to perform a number of tests to determine whether a system with switched consumers is actually going through a start-up phase in the correct manner. For this purpose, signals are read in by the microprocessor and compared with setpoints. In the event of a faulty consumer status, the microprocessor switches the consumers off. The signals are supplied by isolation amplifier circuits, which are fed with voltages which are applied to the switched consumers.

In the isolation amplifier circuits, for example, optocouplers are used as isolation elements for the galvanic isolation of the monitored system from the microprocessor. The individual isolation amplifier circuits each deliver a binary signal which corresponds to a state - switched on or switched off - of the corresponding consumer.

Optocoupler applications of this type are known from the specialist literature (Tl-Opto cookbook from 1975, ISBN 3-88078-000-5).

However, the separating elements have the disadvantage that they are not fail-safe and therefore have to be checked for a signal pretense in safety-critical applications even in an active operating state. Such a check, which is necessary in the application described, is expediently carried out in the region of the zero crossing of an AC voltage to be monitored, while the AC voltage must be interrogated with the greatest possible interference voltage distance in the region of the maximum of the AC voltage.

In order to avoid unwanted safety shutdowns due to short interference signals, a query time window must be chosen as large as possible, on the other hand, the monitored AC voltage must be present within the query time window. The maximum possible length of the query time window is determined by the tolerance ranges of the amplitude and frequency of the monitored AC voltage and by the transmission factor of the separating elements. When using an optocoupler as a separating element, a value range of the transmission factor of x to 6 x can be expected due to manufacturing tolerances and aging influences, i.e. the switching threshold of a sensitive specimen when new can be six times lower than that of an insensitive specimen after a long period of operation; This means that a wide tolerance range and long-term instability can be expected for the time behavior of the output signal at the optocoupler.

The invention has for its object to provide an arrangement for monitoring AC switches that works reliably in a large frequency range and in a large voltage range.

The invention consists in the features specified in claim 1. Advantageous configurations result from the dependent claims.

An exemplary embodiment of the invention is explained in more detail below with reference to the drawing.

Show it:

1 shows an arrangement for monitoring AC switches,

2 shows a signal at a monitored switch,

3 shows an AC voltage detector with a timer,

4 shows the basic course of the signals of the timer,

Fig. 5 shows a digital variant of the timer and

6 shows an input galvanically isolated by optocouplers for the actual information of the AC voltage detector.

In FIG. 1, 1 means an AC voltage detector and 2 an evaluation unit. The AC voltage detector 1 has a first input 3 for a query clock C, a second input 4 for a reference variable Ref, at least one further input 5 or 6 for actual information listi, or I | St2 and an output 7 leading to the evaluation unit 2 for a filtered actual information Im on. The evaluation unit 2 has an additional input 8 with target information isoli and an output 9 for a switch state signal Z.

The AC voltage detector 1 and the evaluation unit 2 together form an arrangement 10 for monitoring at least one AC switch. It is possible to expand the arrangement 10 such that, for example, thirty-two AC switches can be monitored. The output of a first AC switch 11, which switches a consumer 12 to a mains voltage Upg lying between a phase P and a zero point G, is connected to the input 5, while the output of a second AC switch 13, via which a further consumer 14 through the mains voltage Upg is fed, is connected to input 6. The mains voltage Upg serves as the reference variable Ref for the measurement of the grid-synchronous actual information listi or hst2, which is why input 4 is connected to phase P. The AC voltage detector 1 is galvanically isolated from the mains voltage Upg after the inputs 4, 5 and 6. Optocouplers are preferably used for the electrical isolation of the three inputs 4, 5 and 6; however, other suitable elements can also be used.

In response to a query cycle C, which is generated, for example, in the evaluation unit (2), the positions of the AC switches 11 and 13 are changed by the AC voltage detector 1 by means of the sinusoidal actual information lisn and Iist2

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Period of the reference variable Ref is advantageously recorded several times in each case in the case of a positive and a negative half-wave and in the zero crossing. Because the actual information I | Sn and I | St2 is recorded several times and only a corresponding majority of the values recorded in the positive and negative half-wave and in the zero crossing form the filtered actual information Im, short-term faults can already occur in the AC voltage detector 1 be largely suppressed.

The filtered actual information Im is compared in the evaluation unit 2 with the target information Isoli which is caused by the current state of a monitored system and which contains a target state - open or closed - for each monitored AC switch 11 or 13, and the switch state signal Z is then formed. The switch status signal Z contains at least one information unit with a statement - error or no error - in total for all AC switches 11 and 13 occurring. When forming the switch status signal Z, the values for the filtered actual information Im recorded in at least one previous evaluation cycle are also taken into account , the reliability of the switch state signal Z increases.

2a and 2b show a signal of a monitored switch - the line voltage Upg switched by the AC switches 11 and 13 - each with an upper and a lower tolerance limit value for the amplitude and the frequency. For example, the two tolerance limit values of the amplitude apply with 70% and 120% of the nominal value of the mains voltage Upg and the two tolerance limit values of the frequency with 80% (FIG. 2a) and with 130% (FIG. 2b) of the nominal value fn the frequency of the mains voltage Upg .

Since the actual information listi or Jist2 is transmitted before the detection in the AC voltage detector 1 by a galvanic isolating element, for example by a non-fail-safe optocoupler, it is expedient to also check the corresponding isolating element with the AC switch 11 or 13. The separating element is advantageously checked for a signal simulation in the area of the zero crossing of the line voltage Upg - in a test window Faus - while the actual information listi or Iist2 is reliably checked in the area of the maximum amount of the line voltage Upg - in a further test window FIn. A temporal query window A used by the AC voltage detector 1 to record the actual information listi or I | St2 must lie within the possible test window FEin.

With increasing frequency of the mains voltage, the start time tAO of the query window A is closer to a preceding zero crossing of the mains voltage, so that the actual information listi or Iist2 can be reliably detected in a large frequency range and in a large voltage range. The start time tAO is generated by the AC voltage detector 1 as a function of frequency.

3 shows the basic structure of the AC voltage detector 1 from a timer

15 and an interrogation unit 16. The input 4 of the AC voltage detector 1 leads in the timer 15 to a first low-voltage switch 17 for the positive half-waves of the reference variable Ref and to a second low-voltage switch 18 for the negative half-cycles of the reference variable Ref. The output of the threshold switch 17 with a signal Hp leads on the one hand to an input of the interrogation unit 16 and on the other hand to a first input of an OR gate 19, while the output of the threshold switch 18 leads with a signal Hn to a further input of the interrogation unit 16 and additionally to the second input of the OR gate 19 whose output is connected with a signal H to the input of a bipolar current source 20. The output of the current source 20 with a signal I is connected to the input of an integrator 21, the output of which leads with a signal U to a third low voltage switch 22, which has a switching level close to zero, and whose output for a signal Ft to a further input of the interrogation unit 16 connected is.

The inputs 3, 5 and 6 of the AC voltage detector 1 and also its output 7 are identical to the identically labeled connections of the interrogation unit 16.

The two switch switches 17 and 18 galvanically separate the timer 15 e.g. by an optocoupler from the mains voltage Upg. In addition, the sulfur switch 17 generates the binary signal Hp shown in FIG. 4, which indicates the presence of a positive network half-wave, while the sulfur switch 18 forms the binary signal Hn, which detects a negative network half-wave. The OR gate 19 forms the binary signal H from the signals Hp and Hn, which signals the zero crossings of the mains voltage Upg with H = “0”. The signal H controls the bipolar current source 20 in such a way that a current I which is constant in two sections feeds the integrator 21 in a positive manner, for example on the one hand in time sections with H = "0" and on the other hand in a negative section in time sections with H = "1". The integrator 21 delivers at its output a substantially triangular, periodic signal U with a positive ramp caused by the positive section of the current I and a subsequent negative ramp which is generated by the negative section of the current I. The signal U causes at the output of the downstream threshold switch 22 a binary, rectangular signal Ft, the frequency of which has twice the value of the frequency of the mains voltage Upg and the pulse width of which is dependent on the two amounts of the current I. If its amount is increased in the positive section of the current I, the peak value of the signal U becomes larger and thereafter the duration of the negative ramp of the signal U becomes longer with the same slope. The duration of the negative ramp of the signal U also increases when the amount of the current I is reduced in its negative section; in this case the slope of the negative ramp decreases in amount. If at least one of the two amounts of the current I is changed, the signal U also changes

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the pulse width of the signal Ft; essentially the time of the negative edge of the signal Ft depends on the current I. It is also possible to additionally change the pulse width of the signal Ft via the switching threshold of the threshold switch 22.

The signal Ft can also be used in other ways e.g. digitally generated. In this case, known disadvantages of the analog circuits, such as an incorrect deviation of the output voltage in integrators influenced by various parameters, are eliminated.

In a variant of the timer 15 ′ shown in FIG. 5, the bipolar current source 20, the integrator 21 and the sulfur switch 22 are replaced by a digital circuit comprising an oscillator 120, a multi-stage counter 121 with a switchable counting direction and a logic block 122. The counter 121 has a clock input, which is connected to the output of the oscillator 120, and a control input, to which the output of the OR gate 19 is connected. Several inputs of the logic block 122, which generates the signal Ft at its output, are connected to outputs of the counter 121. The output signal H of the OR gate 19 controls the counting direction of the counter 121, with which the constant output pulse of the oscillator 120 can be counted. The counter 121 is constructed in such a way that it counts in a positive direction synchronously with the pulse frequency of the oscillator 120 after each negative flank of H (FIG. 4) when H = “0” and for so long after the positive flank of H the same counting frequency until it reaches zero again. The counting time, that is to say the time during which the count value of the counter 121 is not zero, can be influenced by the pulse frequency of the oscillator 120 and the step size of the counter 121, which can be different in both counting directions. The logic block 122 generates the value “1” for the signal Ft if the count value of the counter 121 is greater than zero, and the value “0” if the count value is zero. The signal Ft thus has a negative edge which can be shifted in time within wide limits.

With increasing frequency of the reference variable Ref, the negative edge of the signal Ft appears closer to the previous zero crossing of the reference variable Ref, since its edge steepness increases, while the switching thresholds of the switch switches 17 and 18 are constant. The signal Ft has exactly twice the frequency of the reference variable Ref. The negative edge of the signal Ft is used for frequency-dependent determination of the start time tAO in the positive half-wave or tAO 'in the negative half-wave of the query window A in the query unit 16 (referring to a previous zero crossing) ( Fig. 3). Because the negative edge of the signal Ft can be shifted within wide limits, the start time tAO or tAO 'and thus the query window A can be optimally positioned within the half-wave - for example in the middle of the half-wave - so that the actual information is listed or Iist2 can be reliably detected.

The length of the query window A also results in the necessary length of the test window Fen

(Fig. 2a) while the actual information listi or Iist2 is available at input 5 or 6; the test window FEin must at least cover the query window A. For this purpose, the optocoupler circuits at the inputs 5 and 6 of the interrogation unit 16 are dimensioned in a known manner.

In the interrogation unit 16, on the interrogation cycle C, the positions of the AC switches 11 and 13 via the actual information listi and Iist2 are read and stored in a known manner in each case in an interrogation window A with a positive and with a negative half-wave. In order to suppress short-term disturbances, this recording of the actual information listi and l | St2 is advantageously carried out several times when Hp = "1" and also several times when Hn = "1".

With Hp = "0" and Hn = "0", which corresponds to a range of the zero crossing, the separating elements are checked for a signal simulation by further recording of the actual information listi and l | St2. On the basis of this check, it is possible to generate an error signal F which contains the state - good or defective - of each separating element and which can be passed on to the evaluation unit 2 via an additional output 23 (FIG. 1).

6 shows, as an example of a circuit construction of the two inputs 5 and 6, the input 5 of the interrogation unit 16 (FIG. 3) or the AC voltage detector 1 (FIG. 1), which is galvanically isolated by optocouplers, for the actual information listi. A resistor 24 and a capacitor 25 connected in series therewith form a low pass 26, at the output of which the input circuit of an optocoupler 27 is connected in parallel with the capacitor 25, the output circuit of which generates a signal listi 'which is dependent on the actual information listi but is separate from its potential . The low-pass filter 26 with the capacitor 25 has several advantages over an ohmic voltage divider: on the one hand, short interference pulses - or interference with high-frequency harmonics - are short-circuited by the capacitor 25 and, on the other hand, a fault voltage coupled in via a parasitic line capacitance 28 or 29 with a minimal power loss effectively divided, so that the arrangement has a far higher compatibility for the line capacitance 28 or 29 acting between the connection of phase P and the input 5 or 6 or a responsible, not ideal line routing between the consumer 12 or 14, the AC switch 11 or 13 and the input 5 or 6 results. Another advantage of the low-pass filter 26 is that the AC switch 11 or 13 is loaded with the charge current of the capacitor 25 without additional power loss. As a result, the AC switch 11 or 13 switches more reliably, especially when the consumer 12 or 14 has a high resistance.

Claims (1)

Claims 1. Arrangement of an AC voltage detector (1) and an evaluation unit (2) for over 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 4th 7 CH 682 608 A5 8th Monitoring of AC switches (11; 13), the AC voltage detector (1) having a first input (3) for a polling cycle (C), at least one further input (5; 6) for actual information (listi; Iist2) and one for the evaluation unit ( 2) has leading output (7) for filtered actual information (Im) and wherein the evaluation unit (2) has an additional input (8) with setpoint information (Isoli) and an output (9) for a switch status signal (Z), characterized in that the AC voltage detector (1) has a reference input (4) for a reference quantity (Ref) and that a start time (tAo; tAO ') for a query window (A) for querying the actual information (listi; hst2) in the AC voltage detector (1) referring to a zero crossing of the reference variable (Ref) and closer to the zero crossing with increasing frequency of the reference variable (Ref), so that the actual information (listi; Iist2) is acquired independently of the frequency with the query window (A) is cash. 2. Arrangement according to claim 1, characterized in that the AC voltage detector (1) contains a timer (15) with which the start time (tAO) for the query window (A) can be generated in a frequency-dependent manner from the reference variable (Ref). 3. Arrangement according to claim 2, characterized in that the timer (15) has a first sulfur switch (17) for the positive half-waves of the reference variable (Ref) and a second sulfur switch (18) for the negative half-waves of the reference variable (Ref) that the outputs of the two threshold switches (17; 18) are led to an OR gate (19), the output of which is connected to the input of a bipolar current source (20) with a downstream integrator (21), the output of which is connected to the input of a third threshold switch ( 22), the output signal (Ft) of which has an edge for determining the start time (tAo) of the query window (A). 4. Arrangement according to claim 2, characterized in that the timer (15) has a first sulfur switch (17) for the positive half-waves of the reference variable (Ref) and a second sulfur switch (18) for the negative half-waves of the reference variable (Ref) that the outputs of the two sulfur switches (17; 18) are led to an OR gate (19), the output of which is connected to a control input of a multistage counter (121) with a switchable counting direction, which has a clock input and a plurality of outputs, the clock input being connected to the output of an oscillator (120) and the outputs leading to inputs of a logic block (122) whose output signal (Ft) has an edge for determining the start time (tAo) of the query window (A). 5. Arrangement according to one of claims 1 to 4, characterized in that each input (5 or 6) of the AC voltage detector (1) is electrically isolated. 6. Arrangement according to one of claims 1 to 4, characterized in that each input (5 or 6) of the AC voltage detector (1) is galvanically separated by an optocoupler (27). 7. Arrangement according to claim 6, characterized in that the input circuit of the optocoupler (27) is parallel to a capacitor (25) which has a low-pass filter (26) for the actual information (ljsti) with a resistor (24) connected in series with it. forms. 8. Arrangement according to claim 6 or 7, characterized in that the AC voltage detector (1) has a further, leading to the evaluation unit (2) leading output (23) for an error signal (F), the state - good or defective - of all optocouplers ( 27) at the inputs (5; 6) of the AC voltage detector (1). 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 5