SU69768A1 - Bridge for measuring grounding resistance - Google Patents

Description

The bridges of Kohlrausch and others that were used earlier for measuring transient resistances and others have two main disadvantages:

1) the need to install two devices; 1 ground gens, which is very difficult in mine conditions; 1, and

2) the need to produce mathematical calculations of the measurement results.

By: Tutorial Widespread Shtersse.ch bridge requires only one auxiliary ground-shadow and probe, and the measurement results are read directly on a scale.

However, this bridge, in turn, has a number of flaws, from which the guides otdetit;

1) pain and errors in measuring;

2) the impossibility of obtaining a reference when the magnitude of the desired resistance is less than 2 ohms, i.e., at the resistance type, which is most important for mine earthing switches;

3)) It is impossible to measure the resistance of the grounding if the resistance of the auxiliary () 1AH; 1NW of the ground will be small compared with the sought resistance: this circumstance makes it difficult to use the common grounding network of the mine as an auxiliary earth. 1st, when determining resistance to spreading of one e.ectrod.

The subject matter of the invention is a bridge for measuring ground resistance according to the Wieherth method based on the Wheatstone bridge circuit.

According to the invention, in order to improve the measurement accuracy, the two arms of the bridge are made with the same resistance, and the other two arms incorporate adjustable rheostats. This makes it possible, by including the second dimension, and subsequently with the tested ground, a resistance equal to the sum of the indications of the tested and auxiliary replacements, to determine the resistance of the test ground according to ve, for the resistance introduced to balance the bridge in series with the universal grounding m.

FIG. 1 shows a general scheme of the proposed bridge; pas figs. Figures 2 and 3 depict the wiring diagram in two stages of the item measurement.

123 On the diagrams, the following terms are taken: x - grounding, the resistance of which must be determined; auxiliary ground (common ground network); z is the probe; - regul; hirzelshe resistance; - adjustable resistance with a 1klara, scaled to -; a - constant resistance; T - telephone; / 7 - switch; B - intermittent current source. To the beginning; (and the measurement resistance is output completely, and the switch P is in the position /. Further, the resistance; (the measurement / is chosen so that the sound on the telephone T completely ceases and the chip is mipyma; nyl1. In this case; , is shown in Fig. 2. The ratio of the shoulders will be assumed to be: Kj X-hY and R, -x + y. When moving the slide contact along the resistance R., the switch automatically switches from / to position, and a circuit is created shown in Fig. 3. In the equilibrium position, which is achieved by adjusting resistance /. ,, the ratio; / Л + х / Vr-y ТГ or /, f-X. /, -к у. (2) The magnitude of the resistance of the probe with equal arms a has no effect on equality (2) Solving Eqs. (1) and (2) with respect to X, we find; / .. x -2 Thus, from Eq. (3), it can be seen that it is sufficient to have an adjusting resistance /, programmed., Which is dual to that, ng); / y-. Read the measurement of the isolygo resistance directly on the scale. In this case, the accuracy of the instrument is doubled compared with the bridge Shtsestet and it allows determining a single circuit of about 0.2-0.3 ohm. In the proposed scheme, the ms achieved the fact that the desired resistance x is defined by a completely separate regul; (irreducible resistance /, the magnitude of which co-ordination; auxiliary aid; (nd land) does not affect. This circumstance allows you to make the adjustment of resistance R much feel: And) It than It doesn’t have much to do with its overall dimensions, as it is enough to make the ngkalu for blacksaving on 12-13 ohms (and not 100 ohms, like that of the bridge Shteseel). Pes; 1s; gno with adjustable sirotivle} 1e R., but vku.kuytit constant sotrotin-chip in 20 ohms, which is normally short-circuited. If the resistance HcnbiT -eM (jro ground;) will be more than 12 ohms. successively the constant resistance is switched on, and the measurement range is increased to 22-23 ohms. The Bridge d; 1 measurement-resistance; 5 Earthmapping according to the Wiechert method, and with the fact that, with a measure to improve the accuracy of measurements, two of his shoulders are made with the same resistance; The other two points include adjustable resistors so that, by switching on the second dimension in series with the test ground, a resistance equal to the sum of the resistances of the test and auxiliary grounds, can be used to determine the magnitude of the resistance of the test piece of grounding by the magnitude of the resistance, go to balance the pic bridge; with consistent grounding.

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FIG. 3