DE1088112B - Circuit arrangement for checking contacts arranged in direct current circuits for their switching position - Google Patents

Description

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NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL. ·

SEPTEMBER 1, 1960

When investigating systems of telecommunications technology, in particular systems of telephone and Teletyping technology, it is often required to operate electrically or instantaneously Determine the position of contacts in DC circuits. This is particularly the case with contacts which, such as B. thermowell contacts, are subjected to direct observation.

In such a contact test, the use of known aids, such as resistance measuring bridge, Doorbell box, buzzer and headphones, etc., various disadvantages entailing the test make it difficult or impossible. For example, an operating potential can be applied to the Contact make the test so difficult that it is necessary to intervene in the DC circuit which the circuit is partially put out of operation. It can also cause the DC circuit are caused by the fact that the DC circuit is influenced by the tester will. This is, for example, in an already known testing device for telecommunications systems Case in which a glow lamp is installed in the primary circuit of a transformer fed by an alternating current source is switched, 'which light up differently (weak or strong) when idling or under load of the transformer serves as a test criterion for current continuity. In this test facility, there is an influence of the circuit part to be tested to the extent that this circuit part has a considerable effect Energy must be supplied to a clearly recognizable difference in brightness in the indicator glow lamp to be able to perceive. There are also facilities for the determination of interference contacts known, in which to test at the input of the. DUT an alternating voltage is placed and the DUT is shaken by lightly knocking, so that occurring at a faulty contact point Changes in resistance, the amplitude of the alternating voltage is interference-modulated. The application devices of the latter type continue to occur, as does the use of a buzzer of noises. This is particularly disadvantageous in telephony circuits, since it results in it the conversations are disturbed.

The above-mentioned deficiencies are avoided by the invention. The invention relates to a circuit arrangement for testing contacts arranged in direct current circuits for their switching position using an oscillator that can be connected to the contact. This circuit arrangement is characterized that in the oscillator the quality of the resonant circuit by the respective switching position of the to be tested Contact is controlled in such a way that: Circuit arrangement for testing

of in DC circuits

arranged contacts on their

Switching position

Applicant:
Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Witteisbacherplatz 2

Dipl.-Ing. Rudolf Hannig and Dipl.-Ing. Günter Raab,

Munich,
have been named as inventors

the oscillator oscillates when the contact is open and does not oscillate when the contact is closed.

The circuit arrangement according to the invention can be placed directly on the contact to be tested, without interfering with the in .. operating state DC switching is required and without mutual interference. The one to be tested The contact is conveniently coupled to the resonant circuit via a transformer winding. Included the transformer winding can be protected by a capacitor against direct currents from the contact to be tested containing direct current circuit are blocked.

The oscillator can consist of a simple transistor oscillating stage that operates at a frequency above the audio frequency range is tuned. The use of a transistor oscillating stage is permitted it is possible to get by with a small supply voltage, such as that provided by a battery. It will thereby the independence of the test device from a network connection is achieved. The usage of AC voltages with a frequency that is above the audible range for testing contacts in DC circuits has the advantage that no acoustic disturbances occur through which z. B. existing Conversations could be influenced. The AC voltage entering the DC circuit is so small that it does not cause any other disturbances.

The oscillator's state of oscillation or rest can be indicated optically or acoustically.

The principle according to the invention, the good, the resonant circuit depending on the state of the Changing the test object can not only be done with the

009 589/111

Use test of a contact, but also when it is to be determined whether the resistance of a circuit part is above or below a certain value. By appropriately dimensioning the Test circuit can namely achieve that the oscillator at certain values of the resonant circuit damping resistance oscillates or is at rest. In a further embodiment of the Finally, the invention can also determine the size of the resistance of a circuit part, with the oscillating state of the oscillator is used to display the resistance value.

The invention will now be explained in more detail using an old management example.

1 shows a circuit arrangement according to the invention for testing contacts in direct current circuits. The resonant circuit UI, Cl of a transistor oscillator with the transistor Tl is tuned to a frequency above the audio frequency range, for example to 25 kHz. The oscillator is excited to oscillate via a feedback winding Uli and an adjustable feedback resistor 2-4. Three resistors R1, R2 and i? 3 are used to generate a bias voltage for the transistor electrodes; for the alternating voltage, the two resistors R 2 and i? 3 are bridged by the capacitors C 2 and C 3. With a supply voltage U of, for example, 2.4 V, which is supplied by a battery, an alternating voltage of around 1 to 1.7 V is obtained on the resonant circuit.

The resonant circuit can be dampened as desired, ie its quality can be changed via the winding III of the transformer Ü. This happens e.g. B. by the contact to be tested k. In the present application, only the two states "contact open" and "contact closed" are of interest. A resistor R 5 in series with the transformer winding III is therefore dimensioned so that the oscillator oscillates when the contact is open and at closed contact with a contact resistance 6 of a maximum of 10 ohms. A capacitor C 4 prevents direct currents from flowing through the transformer winding Ü III from the direct current circuit containing contact k. 5 of the winding Ü III is about 0.5 V, on the other hand it is so low that it does not cause any interference there.

When dimensioning the test circuit, it must be taken into account that in a system in the operating state, the contact k cannot generally be examined on its own, but that any ohmic resistances R, inductances L and capacitances C can be shunted to it. The contact can also be at a certain potential. Examples of such shunts, Figs. 2 to 5. In the inventive circuit of FIG. 1, this potential shunts are k to the contact taken into account so that the contact k even then open as "" is checked, that is that the oscillator already oscillates when the contact has a shunt impedance with an active component of at least 100 ohms.

An indicator S is used to display the oscillating state or the state of rest of the oscillator. The power required for this indicator is supplied by an amplifier stage with a transistor T2 .

This amplifier stage is coupled to the resonant circuit of the oscillator via a winding ÜIV. The current for the indicator is set by changing the negative feedback resistance i? 8 in the amplifier. If, with an ohmic resistance R = 100 Ohm, the greatest permissible damping of the resonant circuit is present with an open contact, which should still be displayed as "open", the lowest display current for the display at this value of R is set.

Instead of a flag, of course, another display means, e.g. B. an ammeter. The ammeter can be calibrated in resistance values so that the size of the shunt resistance can be read off directly. An acoustic display device can also be used be used. However, the use of a small flag has the advantage that this is special cheap in a handheld tester, z. B. an enlarged test probe can be installed.

Claims (7)

Patent claims: 1. Circuit arrangement for testing contacts arranged in direct current circuits on their switching position (open, closed) using an oscillator which can be connected to the contact, characterized in that the quality of the resonant circuit in the oscillator is controlled by the respective switching position of the contact to be tested (k) in such a way that the oscillator oscillates when the contact is open and does not oscillate when the contact is closed. 2. Circuit arrangement according to claim 1, characterized in that the contact to be tested (k) is coupled to the resonant circuit via a transformer winding (Ü III). 3. Circuit arrangement according to claim 2, characterized in that the transformer winding (Ü III) by a capacitor (C 4) against direct currents from the. DC circuit containing contact (k) to be tested is blocked. 4. Circuit arrangement according to claim 3, characterized in that the oscillator consists of a simple transistor oscillating stage, which is set to a frequency above the audio frequency range is matched. 5. Circuit arrangement according to claim 4, characterized in that the oscillating or resting state of the oscillator is indicated by an indicator (S ) which is fed by a transistor amplifier (T 2) coupled to the oscillator's resonant circuit via a transformer winding (ÜTV). 6. Circuit arrangement according to one of the preceding claims, characterized in that the oscillator oscillates when testing an open contact (k) which has a shunt with an effective resistance of at least 100 ohms. 7. Circuit arrangement according to claim 6, characterized in that to display the Oscillation state of the oscillator. ammeters calibrated in resistance values are used will. Considered publications:
German Patent No. 683 581;
Elektro-Technik, 1958, issue 3, pp. 19 to 21. 1 sheet of drawings ® 009 589/111 8.60