SU83583A1 - Displacement measuring device - Google Patents

Description

In electric methods of recording and measuring non-electric quantities, an induction method has been widely used to convert the recorded value into a change in the inductance of the throttle included in the bridge circuit fed by alternating current. At the same time, it is required that the frequency of the supply current exceeds the frequency of the recorded process, which, when registering fast processes, is achieved by using high-frequency current generators and complicates the apparatus, as well as the device as a whole.

In the described device, with the elimination of this drawback, the induction sensor is made three-phase, which allows, with direct supply of the circuit with a three-phase current of industrial frequency, to register fast processes of a higher frequency voltage than the supply current.

FIG. 1 shows a diagram of a three-phase induction sensor; in fig. 2 - electric circuit of the device; in fig. 3 is a graph showing the time variation of the current passing through the recording loop loop.

Depicted in FIG. 1, the induction sensor of the device is a three-phase choke with coils 2 and 3 located on the W-shaped core 4. The choke has a movable measles 5. The arrows in FIG. 1 shows the possible directions for non-displacement of the core. When moving the roots, the inductance values of the coils 1, 2, 3 change.

Each of the coils, 2, 3 chokes is included in the corresponding bridge 6 (Fig. 2). Transformers 7 are connected to the diagonal of bridges 6, with which the voltage of the unbalance of the bridges is transformed into a multiphase (in Fig. 2 into a six-phase) voltage. Valves 8 serve to rectify this voltage. The rectified voltage is recorded using an oscilloscope loop 9. The device is powered by a three phase voltage of industrial frequency.

If there is no impact on the sensor, the bridges are in a balanced state, and the current in the loop will be zero. When moving the core of the sensor, the inductance of its three coils simultaneously changes, causing imbalance of the bridges and, depending on its degree, the flow in the loop of more or less direct current, the graph of which is shown in FIG. 6 for a six-wavelength rectification. at short-term displacement of the sensor core. Provided that the frequency response of the transformers is linear, we obtain pulses as shown in FIG. 3 Here ig denotes the current in the loop with a long and relatively large inductance change, 4 - current in the loop with a long and relatively small change in inductance, ii and 12, respectively, the curves of current pulses with large and small short-term inductance changes.

The short-term processes occurring in the circuit during a single reciprocating motion of the core will have instantaneous magnetic flux values in the sensor cores with a fixed core;

Fh Fta Sincot

 + 120) (1)

Ф8 Фшах-ЗшИ + 240 «) J

Under the influence of mixing, the fluxes Ф Ф Ф Ф and Ф will receive prirash, eni AF1, DF2, and DFs.

In this case, in the coils of the sensor, e.d. s will be induced.

d (f, + df) 1

D - U7

, (.one

M (1 (FZ + AFZ)

/ 3 - 1

Since the duration of the recorded pulse is much less than the period of the power supply, its voltage, the values of the fluxes Ф Ф Ф-2, Фз during the time interval of the pulse can be considered constant, then the equation-ibni (2) is simplified, taking the form:

w (f,) dt

dt

w

dt

The resulting emf will create currents in external transformers, determined from the ratios:

(2)

(3)

The excess of the inductive resistances of the circuits over the active, achievable at frequencies higher than 50 Hz, is expressed by the dependence:

dt

r

dt

r di; I- -f / Substitute in expression (4) the values of i, 4, 4 from expression (3) and neglecting condition (5) of the members tlr,,, and we get:

tu / d (AF1), d / i

rfidt

Y (DF,)

From here, the currents will be:

In the scheme under consideration, the rectification and summation of the currents / 4 and / 3 occurs. In this case, the sum of the absolute values of the currents considered:

io liiH-li2 + l4l - Since the change in fluxes at equal coils of the sensor is: LF, 1 + - LF, AF,

where K is the design factor, and 6 is the change in the gap, then it will be:

(1F1M-1F "1 1Fz1) (10)

1+

As is well known, the algebraic sum of the flows F, 02, and Fz (Eq. 1) for any time point is zero. On the other hand, the sum of the absolute values of the flows for any moment in time “2 Fts. From this it follows that:

(five)

(6)

(1АФ, + 1АФИ + 1ДФз1) - (8) change of the gap in all