SU53839A1 - Device for measuring resistance - Google Patents

Description

The device described below is intended to measure active and reactive resistance at high frequency. It has special advantages when measuring circuits where cos cf is close to unity. The methods currently used are given in this case. very low accuracy. A diagram of one embodiment of the device is shown in FIG. 1. Here, 7, 1 are the terminals to which an AC source 8 is connected, the frequency of which is regulated within the limits required for measurements, and 2.2 are the terminals to which the measured resistance is connected 5. These terminals are interconnected by a segment a two-wire line 6, 6 with which the other is connected; a two-wire line 7, 7. In this secondary line, at the end facing the generator, there is a store of reference active and reactance 4, and at the opposite end is indicator 5.

Let us denote the resistance measured by Zx, the magazine resistance is Zg, the current at the terminals is 2-D, the current through the indicator is 5– / “, the resistance of the indicator is r, the length of the secondary line- /. Then the current at the end of the secondary line remote from the generator (i.e., the current through the indicator) will be:

Wf

And 12

U /,

(one)

g

(r. + z) ctg ml + / waz + wj y

Here, 021 s, I2 and 12 are different wave resistances, the methods for calculating which are indicated by the inventor in the article placed in the Scientific and Technical Collection of the Institute of Communications X ° 17 1936.

In the described embodiment, the measurement is made by selecting the resistance 2e so that the current c drops to zero.

Equating the numerator to zero, we find:

We tti2

Zx g.

or since

WaiWa2 - Wc

We

Wai Wa2 - Oc

Another embodiment of a device for measuring resistances is shown in FIG. 2. Here 1 is a short-circuitor, 2 is a graduated reactance, 4 is a store of appropriately selected resistances, is a rheostat for controlling the current sent by generator 8 to line 6, 6. Indicator 5 should have a scale, preferably linear.

The measurement is carried out as follows. First, using graded variable reactances (e.g., a set of coils and variable capacitors), the reactive component of the measured resistance 3 is neutralized. Resonance is judged by the minimum of the indicator 5. For measuring the active component, first, the current is selected. Let this resistance be r. Pressing the contactor 1, set the indicator readings to maximum with the help of the resistor 9.

In this case, the current / II will be

We

1if

Jii-aa-d-,

where D (Z, + Z,} ctg ml + j (wa, + Q.

Matter 4 should be chosen so that when the resistance to the measurable resistance is a multiple of ten (r = 102, 1009, 1000 Q, etc.), the indicator reads zero. Then, if the measured resistance TI is not a multiple of 10, the indicator 5 directly shows how many times it is more or less than the nearest decimal number. In fact, the current / n will now be:

g, g,

-; .- -

((fi - r ,,)

and since

 - - -0 Therefore, the dependence of the instrument readings on the resistance rj will be linear and, with a suitably graduated instrument, it will directly show the number to which it is needed.

multiply the decimal number of ohms, corresponding to the resistance in the magazine 4, to find the measured resistance. From the obtained active component of the measured resistance, one should subtract the active component of the resistance 2. Since the indicator does not indicate the phase (and hence the sign) of the current / and in relation to the current L, then the same indication will correspond to r, larger and smaller . The resistance is different to both sides and by observing the indicator, you can determine which value to select. Of the}., The resistive resistance will lie between two decimal resistances (Hz), giving the greatest deviation of the indicator.

A third embodiment of a device for measuring resistances is shown in FIG. 3

Here, the measured resistance 5 can either be short-circuited using a switch / or shunted by a certain capacitance 2. The resistance 4, while remaining active, can vary within wide limits. The order of measurement is as follows. Turning on the generator 8 and the measured resistance 3, one achieves the resistance 4 with a minimum of current in the indicator. Then, pressing the contactor /, set the instrument arrow to its original position with the help of rheostat 9. Releasing the contactor 7, we immediately get on the indicator scale the phase angle w or cos or tg®, depending on the graduation of the indicator scale. The sign of the angle cp can be detected by the adventure of a small capacitance 2, which will reduce the readings of the device with capacitance and increase them with inductive. To clarify, we note that by tuning to the minimum of the current in the indicator, we equate the active part of the numerator with expression (1), i.e.

,

®12

where can we find

Zx Now the current in the indicator will be proportional to the unknown resistance X

I P / 11 // I -.

Shorted resistance measured, we get:

/ ;. u / ,.

DA / jo

Adjusting the rheostat 9 and setting the indicator arrow to its original position, we will be able to make a comparison of the two currents L, and / ,,:

/ J, x

f-- tg ..

their

In addition to the described variants of the measuring device,

other variations using the principle of the invention. In addition, all the options described can be easily converted to measure the resistance of asymmetric systems.

Pr.dmet invention.

A device for measuring resistance, characterized by the use of two connected lines, a primary high-frequency generator and connected to the measured resistance, and an electrically connected secondary line, into which the resistance standard is connected at the end closest to the generator the end is a measuring device.

g

figure 1

56I 4

Z.

7: /

five