DE8701530U1 - Protective device for electrically operated devices - Google Patents

Description

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The invention relates to electrically operated, in particular portable, devices that work with liquid media or can be installed in pipes, are permanently or detachably connected to the stationary power supply network by means of a movable power connection cable and have an electronic protective device as a leak protection device or to protect the user from an electric shock according to the preamble of the main claim.

Devices of this type include washing machines and dishwashers (OE 25 39 279), submersible pumps - leak protection -, air bubble dewatering devices (DE 26 31 785), kitchen appliances, hair dryers (EP-A 1831), fan heaters, radiation lamps that are also used in damp rooms - electrocution -.

The electronic protection device responds via heat sensors (probes) and shuts off the water supply in washing machines and dishwashers or the mains in household, kitchen and workshop equipment on two poles. The device is switched off using a magnetic valve (DE 25 39 279) or a relay (DE 26 31 785. EP-A 183I) or by reading a fuse-wire-protected circuit breaker (DE 32 08 1*7).

However, the protective device can become dangerously ineffective,

if a wire breaks in the movable mains connection cable belonging to the device. This wire can be the neutral conductor in double-insulated devices that only require a two-wire mains connection. The device is then not operational.

fShig, but can be switched on or become and then under j

tension. The installation of the protective device saat relay or switch In j

the mains plug of the power cable (DE 26 31 785, EP-A j

I83I) requires &zgr;unIchst a· four-wire cable (two wires each ]

for the power supply and for the control signals to the protective device) and does not offer complete safety, because the broken wire can be one of the heater (probe) wires. This source of danger has not been recognized or taken into account in any of the known proposals. Only in the hair dryer according to EP-A 1831 is protection against mechanical damage provided by double shielding of the wires - individually or together; however, this is not sufficient.

The invention is therefore based on the object of ensuring extensive intrinsic safety in a device and arrangement of the type described with the least possible structural or circuitry expenditure, such that the device is immediately de-energized if the protection fails.

This object is achieved according to the invention by a combination of electronic and mechanical components with the features of claim 1.

The combination according to the invention creates an intrinsically safe protective device which, like other unsecured protective devices, not only switches off the mains voltage in the mains plug irreversibly within a very short time - depending on the design of the circuit breaker - if water penetrates into the device housing, before the user can come into contact with live parts of the device via the penetrating water, but also permanently

25- Mains connection cable carrying mains voltage up to the mains plug Includes protection against wire breaks or insulation damage, which cannot be seen under the sheath but renders the protection ineffective.

Although a wire break is noticeable because the device cannot be put into operation, the undamaged wire can still be used to conduct the mains voltage to earth at open parts of the device,

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such as the heating element of a hairdryer, fan heater or similar and can lead to accidents" especially since the user of a defective device will naively assume that it is completely dead.

A particularly advantageous development of the invention, which does not require any additional effort, is described in the patent claim

The shielding of the signal cable of the probe is used here. This arrangement can also be viewed as if the probe were extended over the mains connection cable to the mains plug.

By including the shielding of the power cable in the protection or monitoring, it is impossible for the accidental immersion of just the power cable of a device, if its insulation is defective, to lead to an electric shock.

Furthermore, the probe installed in the frame housing can also be monitored for its integrity if, according to claim 3, the quiescent current loop is guided over the double parent of the probe.

According to the invention, the overall protection is achieved with a two-core, shielded cable, the shielding of which can be loosely laid, whereas the known solutions require a four-core cable (two current-carrying wires and two signal wires), which is heavier, less flexible and expensive.

Advantageous embodiments are characterized in the further subclaims.

In the following, the invention is explained in more detail in terms of its possible embodiments and advantages using an optimal embodiment example.

The drawing shows the circuit diagram of the protective device for an electrically operated device 30 with a fan motor 37 and a heating register 38, e.g. a hair dryer or a heating conductor, which is connected via a two-core shielded mains connection cable 50 to a mains plug 60 in which the components 6 * 20 of the electronic circuit are housed.

The internal power cables lead from the contact pins 1, 2 |

tions 3a, k* Via the switch contacts 3, k of a two-pole §>

Circuit breaker 5 to terminals 2k, 26, to the dfe wires 21, |

23 of the mains connection line 50. The protective switch , |;. forms in series with a diode 12, a resistor ;.

13 and a semiconductor switch, a thyristor 14, a dia- \

gonale (between points A and C) of a diode quartet 6-9. The resistor 13, together with the capacitor 19 connected in parallel to the thyristor, forms a protection against its over-ignition when the consumers 37, 38 in the device 30 are switched on. The RC element 15, 20, to which the control electrode of the thyristor 14 is connected, serves as protection against short-term heating interference. A transistor stage 16, 17 is connected between the control electrode and the base of the thyristor 14 (point C). The base of the transistor is connected via a resistor 18 to a third terminal 25, to which the shield 22 of the mains connection line 50 is connected.

Wires 21, 23 and shielding 22 of the mains connection are connected to the terminals 31, 32, 33 of the device 30. The load circuit of the device runs from the terminals 31, 33 via the device's internal mains cables Ik, 35 and to the operating switch 36, motor 37 and heating register 38. A line runs from the terminal 32 via the open double line kQ, k) of the probe.

&bull; and «ln*n between these connected resistor 39 and a high-frequency protective resistor kl to a branch of diodes 10, 11,

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which are connected between the power lines 34, 35.

Han recognizes that the diodes 8, 9 of the diode quartet in connector 60 form a second diode quartet with the diodes 10, 11 in the device. In the diagonal of this second diode quartet is the series circuit of transistor 16:&mdash; Base resistor 18 - shielding 22 - probe line 4G resistor 39 - probe line 41 - protective resistor 42, in total, a quiescent current circuit leads from the electronic circuit in the mains plug 60 via the wires 21, 23 of the mains connection line 50 (depending on the phase position of the mains alternating voltage) to the diode pair 10, 11 in the device 30 and back via the double line 40, 4>1 with the resistor 39 lying parallel to it and the shielding 22 of the mains connection line to the base resistor 18 of the transistor stage 16, 17 connected as an emitter follower to monitor the functionality of the entire arrangement. The diode 12 in the diagonal of the diode quartet 6-9 ensures that the ripple DC voltage at points A, B, C has the same phase position (simultaneous zero crossings).

The circuit works as follows:

As soon as the contact pins 1, 2 of the plug 60 are inserted into a mains socket, a small quiescent current of e.g. IQ .uA flows from the shield 22 via the base resistor 18 into the base of the transistor 16 and switches it on. The current of e.g. 200 .uA that occurs in the circuit 15 - 16 - 17 between the points A and C keeps the voltage at the control electrode of the thyristor 14 below the ignition voltage (e.g. 0.6 VJ.

2. If the stirring circuit is interrupted during at least one half-wave of the mains voltage due to a break in at least one wire 21, 23 of the mains connection 50, an interruption in its shielding 22 or a connection error at the terminals 24 - 26,

31 - 33, the transistor 16 is blocked, the voltage at the ignition electrode of the thyristor 14 rises above the ignition voltage (e.g. to 1 V _- ), the thyristor switches the diagonal AC through and the protective switch 5 lying on it is suddenly triggered by the current that occurs and opens its switching contacts 3· 4: the entire arrangement is de-energized.

The circuit breaker is designed in such a way that its off position is irreversible, so that the fault must first be eliminated. Such a switch is described, for example, in Eateotacfcriffc EP-83390.

3. If the impedance of the probe 40 drops sharply due to water entering the device 30, the quiescent current Qb«r rises sharply beyond a predetermined upper threshold and thus

the current in the circuit 16 - 17 increases so much, e.g. to 700 uA, that the voltage drop at the resistor 17 causes the voltage at the control electrode of the thyristor 14 to rise again into the ignition range and the thyristor switches on.

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The thyristor therefore fires and switches off the protective switch 5 as soon as the current in the quiescent current loop falls below a predetermined lower threshold or rises above an upper threshold.

The following cases of damage lead to triggering: Interruption of the loop (cable break or connection error)

The solenoid current falls below the threshold of the quiescent current to zero.

Short circuit of a wire with the shield

(Isolation error)
Shielding earth leak (damaged sheath)

Liquid contact (through water breaking into the device or immersion of the defective connection)

The loop current increases above a threshold.

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The advantages of the protective device according to the invention are its low manufacturing costs, its high level of intrinsic safety and the comprehensive protection of users of electrical devices in the home and workshop that are powered by a mobile mains cable, particularly those used in wet rooms in living areas, in bathing establishments, hospitals ( ^e.g. hydrotherapy) and the like, and its suitability for electrically operated circuit breakers of any type.' In this case, only the probe and its supply cables are to be provided in the device to be protected. The switching elements required for connecting them to the wires and shielding of the mains cable can also be accommodated in a watertight cable entry point, so that only four connection terminals (two each for the double cable of the probe and the mains cables) are required on the device.

IS are required. The electronic ignition circuit, which can be modified in detail compared to the example, with the isolating switch ISBt can be accommodated in a volume of e.g. 20 x 20 x 10 mm, so that the dimensions of the mains plug are only slightly larger than QbI Ich.

Claims (5)

Dr. Harry Gaus, Schwanhelmer Sera&*93,'*6i4ft Benshelm To the German Patent Office ZwelbrOckenstrasse 12 Munich 2 Subject: -Utility model application Protective device for electrically operated devices Claims 1. Electrically operated, in particular portable, device with a movable mains connection cable and an electronic protective device arranged in the mains plug (or an intermediate plug) as a leakage protection or to protect the user, consisting of: a) a probe in the device in the form of an open electrical double conductor (40, 41) that cannot be touched during handling, which changes its electrical impedance value in the presence of liquid, b) an electronic ignition circuit (6 - 20) in the ignition plug (60) with a semiconductor switch (14), at the input of which the signal line that is led from the probe via the short circuit line (£o) and that triggers the semiconductor switch when the impedance value of the probe changes by a specified amount, . c) a mechanical circuit breaker (5) located in the mains cables (3a, 4a) of the mains plug, which is connected to the output H Kit (1 I Il IIIII < Ii ttt * IH t 1(4 *t »·· I III II* ·· I II' 2. the ignition circuit and is triggered by the current occurring when the semiconductor switch* (14) is ignited, marked by d) a two-core power supply cable (50) with a shield (22) inside its sheath, which serves as a signal line from the probe to the ignition circuit, and characterized in that e) a closed-circuit current loop is laid from the ignition circuit (6 - 20) in the mains plug (60) via the wires (21, 23) of the mains connection cable (50) to the (30) and in connection with the double conductor (40, 41) of the probe and with the shielding (22) of the mains connection cable back to the mains plug, over which a direct current flows regardless of the operating state of the device, which, as long as its value is between a lower and an upper threshold, blocks the semiconductor switch (14) within the ignition circuit. 2. Device according to claim 1«,
characterized, that the quiescent current loop is led on the device side via a high-resistance resistor (39) bridging the double conductor (40, 41) of the probe and a branch of diodes (10, W) connected in opposition to one another to the device's internal power lines. 3. Device according to claim 2,
characterized, that the quiescent current loop is guided over the double conductors (40, 41) of the probe. 4. Protective device according to claim 1,
gtcharacterized by &bull;in diode quartet (6-9), which is located between the I· ■ · &igr; I ii IIII f IIIJ << ti »ti fill if* 44· ti f llli» 44 4 44 444IM M14 it 4 4 '&iacgr;&iacgr; 4 * Contacts (3. ¹⁰ ) of the circuit breaker* (5) are connected to the mains connections (3a, ka) and in one diagonal of which an electrical tripping element assigned to the circuit breaker is connected in series with the parallel connection of a thyristor (1*0) and a protective capacitor (19), the ignition electrode of the thyristor being in series with a transistor stage (16 - 18) connected as an emitter follower, to the input of which the shield (22) of the heating connection line (50) is connected. 5. Protective device according to claim 4,
characterized, that in the diagonal between the release element of the circuit breaker (5) and the thyristor OO eke diode (12). 6, Protective device according to claim 4 and 5, characterized in that that a resistor (15) is connected in series with a capacitor (20) parallel to the diagonal, that the ignition electrode of the thyristor (14) is connected between the resistor and the capacitor, and that the emitter-collector circuit of the transistor (16) is connected across the capacitor.