EP0071946B1 - Arrangement for digitally monitoring binary or similar sensors and their control lines - Google Patents

Description

The invention relates to a device for digital monitoring of signaling switches or the like and the associated supply lines for control, in which each signaling switch is assigned antiparallel connected rectifier elements, rectangular supply alternating voltages are impressed on the supply lines and the signals selected on the control the position of the signaling switches or one Show fault on the supply lines.

This preamble refers to an arrangement as is known, for example, from DE-AS 2 542 996.

Industrial processes are increasingly automated today. This usually also increases the number of sensors, e.g. B. switches, buttons, guards, etc., on the individual units. This then also results in an extensive line network that connects these sensors to the central control device - today mostly in the form of a programmable logic controller - with or without a microprocessor. In many cases, errors in such a line network lead to long downtimes, because complex troubleshooting has to be carried out. Depending on the type of industrial plant, e.g. B. mining or chemical industry, surveillance is therefore required by the customer, the errors such as wire break, short circuit, etc. selectively report and should also detect the position of the switch. However, it is not desirable here if the number of line connections is increased by such monitoring.

In a known method, the external sensors are supplied with a sinusoidal AC voltage and, depending on the sensor position, only the positive or negative half-wave to the input of the central control device is passed through a semiconductor circuit on the sensor - in the simplest case two diodes connected in antiparallel. The pending signal can then, for. B. be evaluated such that the occurrence of the negative half-wave on the control means that the encoder is in the first position, the arrival of the positive half-wave, that the encoder is in the second position, the arrival of both half-waves signals a line short and the absence of any voltage reports the line break. In addition, level monitoring can also be provided if necessary in order to detect line deterioration.

It is also known to use a rectangular AC voltage instead of a sinusoidal AC voltage and to derive corresponding signal statements. In both cases, however, relatively complex input electronics are required in the control in order to achieve the necessary evaluation of the incoming signals (cf. e.g. DE-AS 2542996). This is based u. a. ensure that the peripheral signal lines carry clocked signals even in undisturbed operation.

In another known method, an external voltage source, e.g. B. assigned a low-frequency transmitter, which is simultaneously supplied via the signal line.

The input electronics then also takes over the evaluation of the pending signal for each input signal.

The object of the present invention is to simplify the signal evaluation in a device of the type mentioned at the beginning. This object is achieved according to the invention in that a clock AC voltage which is phase-shifted with respect to the first clock AC voltage is connected to each control input via a resistor and the potential curves resulting from the two clock AC voltages at the inputs serve as display criteria. Advantageously, 180 ° is selected as the phase shift.

In this way, the potential curve - d. H. the static level - the status of the line or encoder practically immediately. The additional effort to implement the circuit essentially consists only of the resistor, since the clock signals are present from the outset in the programmable logic controllers normally used today, or are easy to implement by software. With conventional electronic controls, clock generation is also negligible.

In addition to the monitoring of lines and sensors, the clock system itself can advantageously also be monitored. It can also be advantageous if the level of the clock AC voltage is monitored.

• Fig. 1 das Prinzip der Überwachung,
• Fig. 2 eine etwa detailliertere Schaltung im Rahmen einer Steuerung,
• Fig. die Taktwechselspannungen und das Potential (Pegel) an den Eingängen der Steuerung,
• Fig.4 den Ersatz eines Wechselschalters durch einen einfachen Schalter, dessen Stellungen ebenfalls überwacht werden sollen und
• Fig. 5 eine einfache Anordnung zur Überprüfung des Pegels der Taktwechselspannung.

The invention will be explained in more detail with reference to a drawing; it shows

• 1 the principle of monitoring,
• 2 shows a more detailed circuit in the context of a controller,
• Fig. The clock AC voltages and the potential (level) at the inputs of the controller,
• 4 shows the replacement of a changeover switch by a simple switch, the positions of which are also to be monitored and
• Fig. 5 shows a simple arrangement for checking the level of the clock AC voltage.

In Fig. 1, the overall system is schematically divided into two parts, namely once in part 1, which includes the external sensors such as switches, buttons, etc. and the central part 2, which controls, z. B. includes a programmable logic controller with serial data processing. It is the task of recognizing the position of the sensors, of which only one sensor 3 is shown in the drawing for the sake of simplicity, and also of detecting whether the feed lines 8 or 9 to encoder 3 are interrupted or there is a short circuit K between lines 7 and 9.

For this purpose, the transmitters 3 are connected via line 8 to an alternating clock voltage T2, as is shown, for example, in line 2 of FIG. 3. Depending on the switch position a or b, the voltage is then at the rectifier element 4 or at the oppositely polarized rectifier element 5. The rectifier elements 4 and 5 are connected via a common line 9 to the input 61 of the. Digital input module 6 of the controller connected.

In addition, line 10 and resistors 6 of z. B. 2 KΩ at the input? 61, an alternating clock voltage T1 is applied, which is shifted by 180 ° with respect to the alternating clock voltage T2. This clock AC voltage T1 is shown in line 1 of FIG. 3. You can z. B. generated by means of a reversing gate 11 from the clock AC voltage T2.

Provided that the source resistance of the clock AC voltage sources goes to zero, the finite slope of the clock edges is neglected and the resistance of the digital input modules goes to infinity, the two clock AC voltages in connection with the antiparallel rectifier elements 4 and 5 result in one of the lines 3 to 6 shown potential curves P at the input 61, namely, if the encoder 3 is in position a, the potential H at input 61, if the encoder 3 is in position b, the potential L, with a short circuit K between the lines 8, 9 or between different encoder lines, the signal in line 5, which corresponds to the alternating clock voltage T2 and, in the event of a wire break B, the potential curve shown in line 6, which corresponds to the alternating clock voltage T1.

FIG. 2 shows the somewhat expanded form of a circuit-based realization of the basic inventive concept shown in FIG. 1. Here, output stages 12 and 13 are provided as voltage sources for the clock AC voltages T1 and T2, which are addressed by software commands in the context of a programmable logic controller so that they provide the required clock AC voltages T1, T2 at their outputs. With the monitoring, not only the short circuit K between the forward and return lines 8, 9 of the encoder can be detected, but also a short circuit K1 between two adjacent lines 8. In any case, the potential P on the digital input module 6 is a criterion for the state of the relevant encoder 3 and the lines.

In the arrangement shown in FIG. 4, the transmitter is formed by a simple on-off switch 31. In order to be able to monitor the state of the switch and the line here, too, the second switch position is simulated in that when the switch 31 is opened, the transistor 32 becomes conductive, which acts as if the switch 31 as in the exemplary embodiment according to FIG. 1 would have been switched to the other rectifier branch.

5 is used for the level test. For this purpose, a test switch 81 is provided in the course of line 8, after its opening the clock alternating voltage or alternating current can be adjusted in amplitude by changing the resistor 82. The resulting amplitude can be monitored with a measuring device 83. It can be used to check whether z. B. have deteriorated the insulation properties of the lines, for. B. in such a way that with a certain reduction in the test AC voltage no measurement signal is received, although this should be the case if the system is working properly. This level test switchover can occasionally be carried out manually or from time to time automatically by the control system.

The monitoring circuit described here is in principle usable for all electronic controls, but is particularly advantageous for serial programmable logic controls, since these generate the clock without further ado and the clock frequency of the clock AC voltage can be adjusted to the working cycles of the control, e.g. . For example, the encoder and conductor are checked at the beginning or at the end of an encoder interrogation cycle. If the pulse duty factor (pulse pause) of the alternating clock voltages is made asymmetrical, e.g. B. in a ratio of 1: 8, the relevant error case can be indicated optically by short or long flashing.

Claims (3)

1. An arrangement for the digital monitoring of binary sensors (3) or the like and/or associated supply lines (8, 9) to the control unit, wherein each sensor is assigned rectifier elements (4, 5) connected in antiparallel fashion, and alternating rectangular clock pulse voltages (T1, T2) are impressed upon the supply lines, and the signals analysed in the control unit indicate the setting of the sensors or disturbances on the supply lines, characterised in that each control unit input is connected via a resistor (7) to a alternating clock pulse voltage (T1) which is displaced in phase relative to the first mentioned alternating clock pulse voltage (T2), and the potential characteristics (P) which are derived from each of the two alternating clock pulse voltages (T1, T2) at the inputs (61) serve as indication criteria.

2. An arrangement as claimed in claim 1, characterised in that the alternating clock pulse voltages are displaced by 180° relative to one another.

3. An arrangement as claimed in claim 1, characterised in that a device (82) which serves to reduce the signal level by specific values is arranged in the course of the supply lines (8, 9) to the sensors (3).

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