DE3237606A1 - Electronic level switch with self-protecting control unit - Google Patents

Abstract

The circuit arrangement is based on the protection philosophy that an unambiguous function monitoring can only occur if a predeterminable variation of the output variables with time is monitored in the active components. By using the change in these output variables as switching commands for subsequent or preceding switching members and corresponding functional dependence, a self-protecting circuit with unambiguously defined output signal is obtained for the fault case with a simple fault. Such a condition is satisfied since all switching components of this circuit arrangement are periodically operated and thus dynamically monitored for functional capability.

Description

Electronic level switch with self-locking control unit Die The invention relates to a self-locking circuit arrangement for monitoring at least 2 electrical sensors, with one power supply part, one intermittent working impulse generator feeding the sensors, at least two from the output the sensor-controlled holding circuits, which after a predetermined time in their stable Fall back and a monostable multivibrator, which is through a delay element can also be held in the unstable position.

In the household sector, in industry and in other institutions is necessary for damage prevention as well as for the functional process, the To keep the liquid level within predetermined limits or possibly penetrate To automatically pump out water quickly to avoid major damage. There in that last used application it is particularly important that a circuit of this Art, even after many years of use, the condition "breaking in To pump out water ", even in the event of faults within the circuit must, the circuit must be designed to be self-locking.

The known level switches do not meet this requirement.

Since these facilities may not function for years their functional reliability is not ensured over a longer period of time Such facilities must therefore be continuously monitored to ensure that they speak up in an emergency.

Such monitoring is complex and expensive.

The invention is based on the object .a circuit arrangement of the type mentioned to create a constant monitoring of the liquid level using electronic sensors, utnd enables si.ch to monitor itself at the same time, so that a failure of the circuit is recognized or to that switching on or off of the connected machine.

To solve this Aufyabe is provided according to the invention in one Vibration generator, which is built up with two operational amplifiers, triangular waves to generate two operational amplifiers via at least two external sensors are supplied, in which the ignition signals for the same number are independent of each other working monostable circuits are generated. the Outputsiynale the monoflos are fed back to the vibration generator and hold it on when both signals are high. This ensures permanent function monitoring create these components, because each can only be brought back into the insert when both are in the zero position and the triangular oscillations then generated are not derived to ground in the sensors.

In series with the first monostable circuit with a longer running time Another monostable circuit is placed, which the following auxiliary relay with Powered. This circuit can only change the signal from one to zero. of the second monoflop can be ignited. The reset occurs when either the Power supply is interrupted for a minimum time or the zero signals from Monoflop 1 does not occur due to failure because this module got stuck in the insert is.

This ensures that the voltage supply to the auxiliary relay is interrupted if Monoflop 1 remains in the insert during operation.

In an advantageous further development of the invention, this is designed as an opener Auxiliary relay as an interrupter in the excitation circuit. a load relay or a Contactor switched.

This ensures that - even in the event of a failure of the power supply the control contactor or load relay remain energized In the same way of application The circuit can also be carried out by changing the direction of the current on the auxiliary relay that the load relay or the contactor drops out in the event of a circuit failure.

In the following, with reference to Figures 1, 2 and 3 an embodiment of the invention explained in more detail.

Fig. 1 shows the schematic circuit structure.

Fig. 2 shows the waveforms on the amplifier unit.

Fig. 3- shows the pulses at the amplifier output.

If the mains voltage is switched on, it switches the relay or the contactor "13" and the work machine starts to work. If now The level control is switched on via rocker switch "14", flows in Regulated direct current "DC2" from power pack 1 to vibration generator "2", to the amplifier pair "3", for the monostable entry mare "4" with a long charging time, for example 100 ms and to the monostable ignition stage 5 with a much shorter charging time, for example 10 ms.

Now the vibration generator generates triangular and square pulses with a frequency of 10 kHz. The square pulses are over a Base current raised and. directly to the inverting inputs of the amplifier "3" given. The triangular pulses are divided and sent to the sensors "7" non-inverting inputs led by "3". There is now-the falling flank the square pulse intersects with the rising edge of the triangular pulse Fig. 2 square-wave pulses are generated at the outputs of "3", which are dynamically fed into the Setzeingänye of the input "4" and the ignition stage 5 "are coupled.

This sets the outputs of "4" and "5" to one and it flows a current of "4" via the diode "8" to the output stage "6" whereby at the same time the capacitor "8 '" is charged. After the charging time of 5, for example after 10 ms, falls the output returns to the stable zero position. Because this exit into the ignition input the output stage "6" is dynamically coupled, the output "6t goes into the insert position and the auxiliary relay picks up and interrupts the excitation circuit of the load relay "13".

The work machine "15" is thus disconnected from the network. Through a Voltage divider "10" is the voltage in the timing element of the output stage "6" a little below kept the breakover threshold.

Are the triangular impulses through the anyestieyenen fluid level Derived to ground, the output of ignition stage 5 remains in the zero position. the Input level "4" is immediately increased again after the drop switches, because the condition "both stages in zero" is fulfilled and the pulse generator after generated an ignition pulse for about 50 ps. Only when the liquid has reached the switch-on level is exceeded, the input stage 4.t also remains in the zero position and the voltages DC3 and DC4 also go to zero, which means that the auxiliary relay "12" drops out, the load relay "13" or the contactor consequently picks up and the pump "15" begins to promote. The timing element of the output stage "6" is now designed so that when the voltage collapses, the breakover voltage drops quickly and thus the breakdown voltage falls through the voltage divider "10" cuts the defined charge voltage.

As a result, this monoflop tilts back into its stable position. By the delivery of the pump is the liquid level with appropriate design decrease so that the input stage 4 can be tilted back into the one position and the output stage is supplied with power, but it remains blocked because it is only supplied by one Impulse from ignition stage 5 can be placed in the insert position. However, since the corresponding Sensor the pulse for the ignition stage 5, which every 100 ms with a pulse height depending on Sensitivity between 1.6 and 2.2 V and a pulse width of 75 ps initiated If the liquid is discharged to ground, the ignition stage will only be "5" again one is set if the switch-off level is not reached.

In order not to switch on in every switch-off phase of 100 r5 goose step "4" the set output stage "6", tilting into the stable position, is equalized by the capacitor "8 '" these disconnections in connection with the diode "8", so that the voltage DC3 only collapses if the power supply from input stage "4" is more than 14 ms is interrupted.

In the circuit arrangement 9, the capacitor "9 '" is via the resistor "9" "depends on the selected RC combination during the insertion of the input stage "4" is charged, with each switch-off of "4" but again quickly via the diode "9 '' '" unload. The coordination of the R-C-Gli.edes was made so that in the specified Shutdown cycle the maximum voltage below that determined by the voltage divider "10" defined voltage at the timing element of the output stage "6" remains.

If, on the other hand, the input level "4" remains in the insert, it increases Voltage in the capacitor "9 '" and thus also in the timer until the breakover voltage is reached and the output switches to the stable zero position. There is now no setting of "6" more possible because the vibration generator "2" is blocked because of the insertion of "4" remain.

The circuit thus fulfills the established safety condition, that the machine to be controlled is permanent in the event of a fault, depending on the operating conditions is on or off.

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Claims (5)

Claims 1) circuit arrangement for function monitoring of Electrical sensors that respond to environmental influences, with a power supply unit, a pulse generator feeding the sensors and at least two. from the exit the sensor-controlled monostable circuits and a further holding circuit, d a d u r c h e k e n n n z e i. c h n e t that the hold circuit "6" of the monostable Input stage "4" with a longer charging time is connected downstream and only the monostable Circuit "5" with the shorter running time, the other circuit "6" in the insert can put. 2) Circuit arrangement according to claim 1, characterized in that by the zero position of both monostable circuits "4" and 5 an operating signal for the vibration generator "2" is generated via an AND element "11", so that only pulses are sent to the sensors 7 when this condition is met, and when this condition is not met this condition "'7" are voltage-free. 3) circuit arrangement according to claim 1 or 2, characterized in that that the square-wave pulses are raised to a higher voltage level by a base current who- the and in comparators' "3" with the sensors "7" guided triangular impulses in which the impulse amplitudes are variable. 4) Circuit arrangement according to claims 1 to 3, characterized in that that the charging voltage in the timing element of the holding circuit "6" through a voltage divider "10" is kept slightly smaller than the Kippspannuncj and resetting input level "4" is switched off. 5) circuit arrangement according to claims 1 to 4, characterized in that that by a holding circuit "9" the voltage in the timing element of the output stage "6" as long as it is held at the level defined by the voltage divider "10", such as the input stage falls into the zero position at predetermined intervals