DE1008159B - Intrinsically safe control circuit in potentially explosive systems for remote pulse measuring devices - Google Patents

Description

In systems at risk of explosion it is necessary to check the measured values from measuring devices of all kinds to be transferred to the pulse method in such a way that these measuring devices do not pose a risk of explosion develop. This has been attempted to achieve that the pulse generator of such measuring systems because of the contact sparks occurring on them are particularly dangerous, housed in explosion-proof housings became. Such housings are relatively very expensive because they are in accordance with the regulations not only have to be gas-tight, but also pressure-resistant; the latter therefore, so inside her any explosions that occur are harmless. Because of the special execution of such Housing, however, result in great difficulties in the transmission of the movements of measuring organs after the pulse generator. This transmission of motion must either be gas-tight or the bushings required for this are so long and so narrow that No more penetrating explosion flames due to cooling and energy loss to the outside are effective.

Despite the implementation of the protective measures described, the measuring systems in question still sources of danger, for example due to interruptions in electrical lines, defective ones Installation or destruction of switching devices etc. can lead to accidents. To even such sources of danger to eliminate, pulse-controlled telemetry systems have already been designed so that their circuits when interrupted or closed as well as in the event of a short circuit at any point Let ignitable sparks arise. Such control circuits are called intrinsically safe. The practical Spark-free switching can be achieved by electronic and thermal means. Have the former however, the disadvantage that the corresponding facilities are relatively expensive and that usually very high demands on the insulation of the impulse lines must be made, whereby only small transmission distances' are permissible. The latter work too sluggishly for the present purpose.

The invention also relates to an intrinsically safe control circuit for pulse telemeters, in which however, the specified defects have been circumvented. This control circuit is characterized by a Impulse contact that is connected in series with a dry rectifier to the secondary winding of a mains transformer connected AC circuit is connected to the DC terminals of the Dry rectifier switched direct current relay, which controls the pulse remote measuring device and its Compensating current occurring when de-energizing is transmitted via an intrinsically safe control circuit

in potentially explosive systems

for remote pulse meters

Applicant:
Landis & Gyr AG, Zug (Switzerland)

Representative: Dr.-Ing. A. Schulze, patent attorney,
Berlin-Wilmersdorf, Jenaer Str. 14

Claimed priority:
Switzerland from March 5, 1966

Dipl.-Ing, Eugen Tritschler,
Binzgen via Laufenburg (Bad.),
has been named as the inventor

Valves of the dry rectifier compensate by a protective winding, which the secondary winding shielded from other mains transformer windings by one dimensioned so high in a manner known per se Ohmic resistance of the secondary winding that is available in the pulse contact circuit standing energy excludes the formation of ignitable sparks, as well as single-pole sparks Grounding the pulse contact circuit and grounding the mains transformer iron and protective winding.

In the drawing is an embodiment of the

Subject of the invention shown. 1 means a mains transformer with a primary winding 2 and two secondary windings. 3 and 4. The secondary winding 3, which is single-pole grounded, is by means of a Protective winding 5 shielded from the other windings. The protective winding 5 and the iron core 6 of transformer 1 are also grounded.

A pulse contact 7 is connected to the secondary winding 3, which is controlled by a measuring device, not shown, ζ. B. a gas meter is operated. From the cable run to the pulse contact 7 is only the line part shown in dashed lines in the drawing in a potentially explosive area 8. In this Line is a dry rectifier 9 in the known single-phase Graetz circuit, which consists of a Combination of four one-way valves is built, inserted, at whose DC terminals a DC relay 10 is connected to contact 11.

709 508/286

A dry rectifier 12 is connected to the secondary winding 4, preferably also in the single-phase Graetz circuit, although this is not a requirement here. To the DC terminals of this A pulse remote measuring device 13 is connected to the rectifier via the contact 11 of the direct current relay 10, through which the measured variable to be displayed remotely is displayed or registered.

The pulse contact 7 actuated by a measuring device as a function of a measured variable switches the on the secondary winding 3 connected alternating current circuit in pulses. Every time this closes AC current is produced at the DC terminals of the dry rectifier 9, a DC voltage, by which the DC relay 10 is operated. The contact 11 actuated by the latter transmits thereby the impulses of the impulse contact 7 on the impulse remote measuring device 13.

To achieve the intrinsic safety of the control circuit, the following are used at the same time Future precautions have been taken: The secondary winding 3, to which the control circuit is connected is dimensioned so that its terminal voltage has a certain value, e.g. B. 6 volts, does not exceed. Furthermore, their ohmic resistance is so high, in a manner known per se, that that in the event of a short circuit at any point in the control circuit, the available standing energy is insufficient for the formation of ignitable sparks. This condition is after According to current experience, when the highest possible voltage is reached at a terminal voltage of 6 volts Short-circuit current is below 20 mA. By earthing the control circuit, a possible static charging of the same impossible. The transition is made by the earthed protective winding 5 from static charges of the control circuit from the power supply network as well as the If the primary winding 2 is damaged, the mains voltage transfers to the secondary winding 3 prevented. The one that occurs when the control circuit in the DC relay 10 is interrupted Equalizing current is generated via the two rectifier bridge arms that are parallel to the relay winding short-circuited, so that he in the control circuit, especially on the pulse contact 7, not to Effect can come. The contact therefore switches practically without sparks.

The intrinsically safe control circuit for pulse telemeters described has the advantage that it consists of simple and mechanically insensitive switching elements and that to the grounded Control current line no special insulation requirements have to be made. By the last specified circumstance results as a further advantage that between the pulse contact 7 and the Pulse telemetry long distances can be bridged without difficulty.

Claims (1)

Claim Intrinsically safe control circuit in potentially explosive systems for remote pulse measuring devices, characterized by a pulse contact that is in series with a dry rectifier in one there is an AC circuit connected to the secondary winding of a mains transformer, by a DC relay connected to the DC terminals of the dry rectifier, which controls the remote pulse meter and its equalizing current occurring when de-energizing is equalized via valves of the dry rectifier, through a protective winding, which the Secondary winding shields from other mains transformer windings by an in-itself known way so high rated ohmic resistance of the secondary winding that the im Impulse contact circuit available energy results in the formation of ignitable sparks excludes, as well as by single-pole grounding of the pulse contact circuit and grounding of the mains transformer iron and the protective winding. Considered publications:
German patent specification No. 689 761. 1 sheet of drawings © 709 508/286 4.57