Circuit arrangement and method for monitoring functioning of a vibration limit switch and/or a level meter

Abstract

The invention relates to a circuit arrangement for monitoring functioning of a level meter and particularly a vibration limit switch. Said circuit arrangement comprises a first piezoelectric oscillation device (SP) as a transmitter device, a second piezoelectric oscillation device (EP) as a receiver device, an oscillator circuit (O) whose input (P0) and output (P4) are connected to the oscillating devices (EP, SP) during normal operation, the second terminals of said oscillation devices (EP, SP) being located on a common frame potential, and a monitoring circuit for monitoring functioning.; The monitoring circuit is provided with a switching device (S1 to S3) for temporarily paralleling the first and the second oscillation device (SP, EP) and switching the paralleled oscillation devices (SP, EP) in series to obtain a capacity meter (K1, R, K2, K3, SG, IW, P) during a temporary monitoring mode according to a first embodiment, a capacity value (c) being supplied by the monitoring circuit as an indicator for the functioning of the oscillation devices (SP, EP) and / or lines extending to the oscillation devices.

Description

technical field [0001] The invention relates to a circuit arrangement for monitoring the function of a vibration limit switch and to a method for such filling level monitoring. Background technique [0002] Vibration limit switches are often used as critical state measuring devices. For generating and picking up vibrations or oscillations, piezoelectric vibration devices are used. It is generally a problem that, in the event of a malfunction of such a device, it is not permissible to output an incorrect switching state, so that such a device must be functionally monitored. [0003] In order to achieve a high level of safety integration when developing level measuring devices in accordance with the international standard IEC 61508, higher requirements are placed on the corresponding devices with regard to fault situations. A defective device does not allow dangerous failures, so in the event of a fault the device must transition to a disturbance notification state in which ...

AI Technical Summary

Problems solved by technology

The general problem is that in the event of a malfunction of such a device it is not permissible to output an incorrect switching state, so that such a device must be functionally monitored

In practice, it is difficult to provide such monitoring elements for piezo drives due to the often tight space occupied and the high temperatures required

In addition, it is only possible to detect an open circuit up to the monitoring element

Faults occurring directly on the actuator, such as breaking of the wire contacts on the piezo element or damage to the piezo element itself, cannot be detected with such a device

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