NEW INSTRUMENTS AND METHODS OF MEASUREMENT

ELECTRONIC INDICATORS OF MECHANICAL QUANTITIES

L. A. Goncharskii

INTRODUCTION

In recent years, the experimental technique for studying mechanical processes has been enriched by a new class of highly sensitive transducers—electronic sensors of mechanical quantities. These devices are electron-vacuum instruments with movable electrodes that are displaced under the action of the mechanical processes being monitored. Electronic sensors have proved to have high sensitivity, sharply distinguishing them among parametric sensors that operate stably on direct current. This feature of these receivers, which are relatively complex in design and are mechanically controlled electron tubes, makes it expedient in a number of laboratory instruments and applied measuring devices to replace other systems of sensors of mechanical quantities with them; among such devices one may mention, for example, micrometers, dilatometers, dynamometers, strain gauges, accelerometers, and others.

A characteristic feature of electronic indicators is the multiplicity of principles by which they can be implemented, making it possible to construct diverse sensors of mechanical quantities adapted to the solution of widely varying problems in experimental technique.

The subject of our article is a description of certain methods for the most effective mechanical control of the electronic and ionic currents of electron-vacuum devices used as indicators of mechanical quantities, and also an account of certain ways of applying them to the measurement and recording of a number of mechanical quantities characterizing the processes under investigation.

The operation of electronic indicators of mechanical quantities is based, as was already mentioned above, on the use

of direct mechanical control of electron and ion currents passing inside a vacuum device. The essence of this method of controlling electrovacuum devices is basically reduced to changing the geometry of the electric field between the electrodes of the device as a result of the relative displacement of its movable part. At present the following methods of effective mechanical control of electron and ion currents in vacuum devices used as sensors of mechanical quantities are best known: longitudinal, transverse, probe, and differential.

The longitudinal method is based on the displacement of a movable electrode in the direction of the electric field. The bringing together of the electrodes is accompanied by an increase in the electric-field intensity, leading (in electron devices) to a corresponding increase in the anode current. In gas-discharge devices, displacement of the electrode along the electric field leads to a change in the conditions of gas ionization, which determine the conditions of the gas discharge inside the sensor.

With the transverse method of control, the movable electrode is displaced in a direction perpendicular to the electric field of the indicator.

The probe method of control is based on the use of a thin electrode moving relative to the electric field.

Finally, the differential method of control is reduced to the use of an electrode protruding through the slots of a second electrode having a substantially different potential. The depth of penetration of the movable electrode into the slots of the fixed one determines the anode current of the indicator.

Turning to the characterization of the principal methods of mechanical control of the currents of electronic indicators, we shall first consider indicators with longitudinal control.

LONGITUDINAL CONTROL

The simplest system of an electronic indicator with longitudinal control is the diode system[^1], proposed by the author in 1935.

Fig. 1.

Its schematic diagram is shown in Fig. 1. Inside the bulb of the device there are two flat parallel electrodes: a fixed—

... stationary heated cathode 1 and a movable anode 2. The latter is fastened to lever 3, which passes through the elastic (bellows) wall 4 of the reservoir, making it possible to deflect the lever through small angles as a result of external mechanical actions. When lever 3 is deflected in the direction shown by the arrow, the distance between the electrodes of the tube changes, and with it the intensity of the electric field between its electrodes. The anode current \(I_a\) of the diode depends on \(U_a\)—the anode voltage—and on \(a\), the distance between the electrodes, and is expressed by the relation

\[ I_a=\frac{A\cdot S\cdot U_a^{3/2}}{a^2}\ \text{amperes}, \tag{1} \]

where \(A=2.34\cdot 10^{-6}\), and \(S\) is the active surface of the plane cathode in \(\text{cm}^2\).

It follows from relation (1) that displacement of the anode by \(\Delta a\) leads to a change in the anode current of the diode being described by

\[ \Delta I_a=-\frac{2A\cdot S\cdot U_a^{3/2}}{a^3}\,\Delta a . \tag{2} \]

Let us define, in the following way, the static differential sensitivity of the indicator with respect to current

\[ \psi_{\text{d}}=\left(\frac{\partial I_a}{\partial a}\right)_{dU_a=0}, \tag{3} \]

with respect to voltage

\[ \varphi_{\text{d}}=\left(\frac{\partial U_a}{\partial a}\right)_{dI_a=0}, \tag{4} \]

and also the differential internal resistance

\[ R_{\text{d}}=\left(\frac{\partial U_a}{\partial I_a}\right)_{da=0}. \tag{5} \]

Using relations (1), (3), (4), and (5), after transformations one can obtain, respectively, expressions characterizing the principal parameters of the indicator:

\[ \psi_{\text{d}}=-\frac{2A\cdot S\cdot U_a^{3/2}}{a^3}, \tag{6} \]

\[ \varphi_{\text{d}}=\frac{4U_a}{3a}, \tag{7} \]

\[ R_{\text{d}}=\frac{2a^2}{3A\cdot S\cdot U_a^{1/2}}. \tag{8} \]

The characteristics of the dependence of the current sensitivity of the indicator on displacement for several anode voltages (with \(S = 0.1\ \text{cm}^2\)) are given in Fig. 2. Fig. 3 shows the characteristics of the dependence of the voltage sensitivity of the same indicator on displacement.

Fig. 2.

The sharply pronounced nonlinearity of the basic characteristics of the diode system makes it necessary to construct paired diode indicators intended for operation in bridge circuits, which make it possible to obtain sufficiently linear characteristics of measuring devices. The basic circuit of a paired diode indicator is shown in Fig. 4. Its action reduces to the following. When anodes 2 and 3 are displaced relative to the heated cathode 1 in the direction shown by the arrow, the distance between cathode 1 and one of the anodes increases, while the distance between the cathode

Fig. 3.

and the second anode decreases. As a result, the ratio of the electron currents to the anodes changes, accompanied in turn by a corresponding change in the current in the diagonal of the bridge circuit shown in the same figure. From the design point of view it is more expedient to make the anodes movable rather than the cathode.

Precisely in this way modern mechanically controlled longitudinal-control diodes are made.

Fig. 4.

Mechanically controlled longitudinal-control diodes possess high current sensitivity with relatively low voltage sensitivity.

INCREASING VOLTAGE SENSITIVITY

We shall describe two known\(^{2,6}\) methods for increasing the voltage sensitivity of electronic longitudinal-control indicators.

One of them is based on increasing the internal resistance of the tube by placing, between the fixed heated cathode 1 and the movable anode 2, a fixed grid 3, as shown in Fig. 5, a. Placing a fixed grid between the cathode and the anode makes it possible to increase the electric-field intensity at the surface of the latter while simultaneously reducing the electric-field intensity at the surface of the heated cathode.\(^{2}\) Since the voltage sensitivity of an electronic longitudinal-control indicator turns out to be numerically equal to the electric-field intensity at the surface of the flat movable anode,

\[ \varphi_{\mathrm{д}} \simeq E_a, \tag{9} \]

partial shielding of the cathode by the fixed grid, making it possible to increase the electric-field intensity by increasing the anode voltage, permits a considerable increase in the voltage sensitivity of the indicator, with a sharp decrease in the anode current. The latter, in turn, makes it possible to increase the voltage sensitivity of the indicator while reducing the power dissipated in it and, consequently, with greater stability of its operation.

Figure 5, b shows a photograph, and Fig. 5, c a section, of a vibrotron, which is a longitudinal-control triode with a movable anode.

L. A. GONCHARSKII

The second method of obtaining an electronic indicator for longitudinal control with high voltage sensitivity is based on the use of the dependence of the voltage drop between electrodes, in a hindered glow discharge, on the distance between them.

Fig. 5.

Labels in Fig. 5в: metallic diaphragm; swinging rod; anode; grid; cathode; metal casing; heater; evacuation tube.

The schematic of an indicator of this type is shown in Fig. 6. It is a gas-discharge diode in which the pressure is selected so that between the fixed anode 1 (surrounded by glass on all sides except for the discharge gap between the electrodes) and the movable cathode 2 a hindered glow discharge is obtained.

Fig. 6.

In this case the dependence of the voltage drop across the indicator on the distance between the electrodes has a form that makes it possible to obtain high voltage sensitivity.

TRANSVERSE CONTROL

Transverse control of electronic indicators is reduced, as was already mentioned above, to displacements of the movable electrode in a direction perpendicular to the vector of the electric field. In Fig. 7, a, a diagram is shown of an electronic indicator with transverse control, in which the displacement of a thin incandescent cathode 1 in the direction shown by the arrow is accompanied by a change in the distribution of the electron currents between anodes 2 and 3. The diagram also shows a cold cathode 4, which promotes the formation and concentration of the electron stream, shown by the dotted line.

Fig. 7.

In Fig. 7, b, a variant with several electrodes is shown. In Fig. 7, c, a diagram is given of transverse control of a gas discharge (occurring between a cold or incandescent cathode 1 and an anode 2 through a slit 3), effected by changing the width of slit 3 when one of its walls 4 is displaced in the direction shown by the arrow. In Fig. 7, d, a diagram is shown of transverse control by means of the displacement (in the direction shown by the arrow) of the movable wall 4 relative to two electrodes 1, 2, recessed in the fixed wall 3.

PROBE CONTROL

Probe control² is based on the displacement of a thin directly heated cathode, oriented perpendicular to the electric field, in the direction of the latter. This method of control is called probe control because a very thin incandescent cathode behaves like a probe determining, from the magnitude of the anode current, the potential of that region of the field in which the incandescent cathode is located, relative to the potential of the latter. The mechanism of probe control is explained by the schematic diagram of the indicator shown in Fig. 8, a. The electric field in which the thin incandescent cathode 1 moves is created by electrodes 2 and 3, connected to the poles of the anode battery. Probe 1 is connected to the negative pole of the anode battery, as shown in the same figure.

During operation of the indicator, the heated cathode 1 moves in the direction shown by the arrow, remaining parallel to the equipotential surfaces of the electric field created by electrodes 2 and 3. The strength of the electric field near the heated cathode, which determines the anode current of the tube, depends on the difference between the potential of the region of the electric field in which

Fig. 8.

the probe is located and the potential of the probe itself. The greater this potential difference, the greater the anode current. The rapid increase in the anode current of the tube as a result of the motion of the thin heated cathode in the direction of the anode makes it possible to use probe control for producing highly sensitive indicators of mechanical quantities.

The current sensitivity of the probe indicator as a function of the anode current \(I_a\) and the distance \(b\) between the heated cathode 1 and the cold cathode 3 is expressed by the relation²

\[ \Psi_d = \frac{3 I_a}{2b}\ \mathrm{A/cm}. \tag{10} \]

Its differential internal resistance is equal to

\[ R_{\mathrm{d}}=\frac{2U_a}{3I_a}\ \text{ohm} \tag{11} \]

and the voltage sensitivity is

\[ \varphi_{\mathrm{d}}=\frac{U_a}{b}\ \text{V/cm}. \tag{12} \]

Fig. 9 gives a typical characteristic of the dependence of the indicator anode current on the displacement of the heated cathode 1 at constant voltage, and Fig. 10 gives a typical characteristic of the dependence of the anode voltage on the displacement of the heated cathode 1 at constant anode current.

Fig. 9.

In probe-type mechanically controlled electronic tubes, an economical oxide cathode with direct heating is used. Owing to this, probe indicators are distinguished among other systems of mechanically controlled electronic tubes not only by their high voltage sensitivity, but also by the low

Fig. 10.

power dissipated in the cathode circuit. The basic circuit of a probe indicator shown in Fig. 8, a, in which the moving ...

the electrode is a probe, is not always convenient, since it is often inadvisable to subject a thin stretched filament, located at high temperature, to rapid dynamic loads. Figure 8,b shows the arrangement of a probe indicator in which the moving system consists of cold electrodes 2 and 3, which create an electric field in which probe 1 is located, and Fig. 8,c gives its photograph.

It appears expedient to use probe gas-discharge indicators with a cold or heated probe, whose action is based on the displacement of a thin electrode relative to a wall or to another electrode.

DIFFERENTIAL CONTROL

Differential mechanical control of the electron current\(^3\) is carried out by the penetration of anode plates through the slits of a negatively charged screen, which produces a blocking action. The basic circuit of an indicator with differential control is shown in Fig. 11. The electrode system of the device consists of a heated cathode 1 and slotted electrodes 2 and 3. In one of the latter, which is cold cathode 3, there is a slot-like opening, along which the second electrode 2, which is the anode, can move freely (without touching the edges of the slit) in the direction shown by the arrow.

Fig. 11.

The circuit for connecting the electrodes of this device is shown there as well. The essence of differential control basically comes down to the following: while anode 2 is recessed in the slit of cold cathode 3, which shields from it the heated cathode, a retarding electric field acts on the electrons emitted by the latter, returning them back. By moving anode 2 in the direction of heated cathode 1, we soon detect the appearance of an anode current, which increases rapidly as the anode advances further in the same direction. Differential mechanical control of electron currents proves to be very effective, making it possible to construct electronic indicators of mechanical quantities possessing high sensitivity both in voltage and in current.

ELECTRONIC MICROMETERS

Electronic indicators of linear dimensions have a wide field of application for measuring small displacements and deformations, for checking the linear dimensions of finished products, the geometry of their surface, and the active checking of the linear dimensions of products.

ELECTRONIC INDICATORS OF MECHANICAL QUANTITIES

in the process of their manufacture (i.e., regulation of the working stroke of the machining mechanism), monitoring the motion of the tool during the machining of an article, measuring the displacement of machine-tool parts in production processes, automatic sorting of articles by their linear dimensions, and investigating a number of mechanical processes observed in the study of many physical phenomena^1, 3, 5, 7.

Of the above-mentioned applications of electronic indicators, the best known are electronic micrometers, in which paired diode indicators are usually used, operating in a symmetrical bridge circuit^2, 3. When a pointer galvanometer is connected into the diagonal of the bridge, sufficiently sensitive instruments are obtained, providing a reading accuracy down to 0.1 μ and more, and suitable for work under laboratory and production conditions.

An electronic micrometer with visual readout (the circuit of which is shown in Fig. 12, a, and a photograph in Fig. 12, b) is a convenient remote measuring instrument, in which an ordinary pointer microammeter usually serves as the indicating device. The sensitivity of the electronic micrometer (its division value) can be expressed as

Fig. 12.

\[ \gamma = \frac{\sigma}{\psi_*}, \tag{13} \]

where $\sigma$ is the sensitivity of the galvanometer (the scale division of the microammeter) and $\psi_*$ is the dynamic current sensitivity of the transducer, equal, in the case of a bridge whose arm resistances are all identical, to

\[ \psi_*=\frac{\varphi_{\text{d}}}{R_{\text{d}}+R_{\text{g}}} =\frac{\psi_{\text{d}}}{1+\dfrac{R_{\text{g}}}{R_{\text{d}}}}, \tag{14} \]

where $R_{\text{g}}$ is the resistance of the galvanometer.

Substituting (14) into (13), we obtain:

\[ \nu=\frac{\sigma\left(1+\dfrac{R_{\text{g}}}{R_{\text{d}}}\right)}{\psi_{\text{d}}}. \tag{15} \]

Let us calculate, for example, by formula (15), the sensitivity of an electronic micrometer assembled according to a bridge circuit, under the condition that the transducer is a double-sided diode thermoelectronic indicator with sensitivity $\psi_{\text{d}}=1\ a/\text{cm}$, and that a pointer microammeter with scale division $\sigma=0.2\ \mu\text{a}$ is used for readout and $R_{\text{g}}=4R_{\text{d}}$. With these parameters, the scale division of the electronic micrometer proves to be equal to

\[ \nu=\frac{2\cdot10^{-7}\cdot5}{1}=10^{-6}\ \text{cm}. \]

Using in the electronic micrometer a probe indicator of small displacements with voltage sensitivity $\varphi_{\text{d}}=10^{4}\ \text{V}/\text{cm}$ and an internal resistance of the order of $10^{5}\ \Omega$, and using a galvanometer with a shadow pointer having current sensitivity $\sigma=10^{-8}\ \text{a}$, we obtain the scale division

\[ \nu=\frac{10^{-8}\cdot10^{5}}{10^{4}}=10^{-7}\ \text{cm}. \]

The high sensitivity of electronic micrometers promotes increased interest in their use for monitoring and recording changes in the linear dimensions of controlled bodies in various measuring devices.

SENSITIVITY THRESHOLD OF ELECTRONIC MICROMETERS

The values of sensitivity of electronic micrometers given above are not yet limiting. The use of more sensitive galvanometers, on the one hand, and the selection of optimal parameters of the transducers and of the measuring circuit, on the other hand, make it possible, by comparatively simple means, to construct devices for measuring extremely small displacements, previously measured by means of complex installations$^{4,17}$.

This circumstance makes the question of the sensitivity threshold of electronic micrometers, limited by fluc-

fluctuations of the anode current of the indicators, i.e., primarily fluctuations of the emission of the heated cathode, partially suppressed by space charge.

Assuming that the minimum recorded displacements \(dl_0\) must give currents \(dI_0\) exceeding by an order of magnitude the root-mean-square value of the random oscillations of the electronic current \(\sqrt{\overline{dI_*^2}}\) of the sensor, we obtain a criterion for determining the minimum signal intensity corresponding to one scale division of the measuring instrument and ensuring stable operation of the instrument:

\[ dI_0 \gg 10\sqrt{\overline{dI_*^2}}. \tag{16} \]

Consequently, the minimum displacements reliably recorded by an electronic micrometer are determined, in accordance with (16) and (3), by the relation

\[ dl_0 \gg \frac{10\sqrt{\overline{dI_*^2}}}{\psi_{\text{d}}}. \tag{17} \]

And since \(^{1,2}\)

\[ \psi_{\text{d}}=\frac{\varphi_{\text{d}}}{R_{\text{d}}}, \tag{18} \]

then

\[ dl_0 \gg \frac{10R_{\text{d}}\sqrt{\overline{dI_*^2}}}{\varphi_{\text{d}}}, \tag{19} \]

where \(dI_*^2\) for the saturation current \(^{13}\) is determined from the relation

\[ dI_*^2=2eI_{\text{a}}\Delta f, \tag{20} \]

in which \(e\) is the electron charge, \(I_{\text{a}}\) is the anode current of the sensor, and \(\Delta f\) is the frequency band for which the device is designed.

Substituting (20) into (19), we obtain:

\[ dl_0 \gg \frac{14.1\cdot R_{\text{d}}}{\varphi_{\text{d}}}\sqrt{e\cdot I_{\text{a}}\cdot \Delta f}. \tag{21} \]

Taking the indicator parameters to have the following values: \(\varphi_{\text{d}}=10^4\ \text{V/cm}\), \(R_{\text{d}}=3\cdot 10^4\ \Omega\), \(I_{\text{a}}=3\ \text{mA}\) (at \(\Delta f=1\ \text{Hz}\)), we obtain the sensitivity threshold of the electronic micrometer, determined by fluctuations of electronic emission, of the order

\[ dl_0=3\cdot 10^{-10}\ \text{cm}. \]

In our case the anode current is limited by space charge, which suppresses fluctuations; therefore the sensitivity threshold calculated by us on the basis of (21) proves to have been taken with a large margin. Consequently, the sensitivity threshold of electronic micrometers is determined not by electronic processes inside the indicator, but by thermal displacements of the mechanical elements of the measuring setup.

L. A. GONCHARSKII

ELECTRONIC VIBROMETERS

Electronic vibrometers \(^{8,12}\) are used both for observing and recording vibrations, shocks, impacts, and accelerations in the objects under study, and for investigating mechanical wave processes in various media. An electronic vibrometer consists of an elastically suspended inertial mass and an electronic indicator of its displacements.

In those cases where the device described is used to investigate the displacements of the object being monitored, the natural frequency of the oscillating system of the electronic indicator is chosen to be considerably lower than the frequency of the processes under study. In this operating mode the elastically suspended inertial mass, connected with the movable electrode of the indicator, remains stationary, while the indicator itself oscillates together with the body being studied.

In those cases where the device described is used to study accelerations, its natural frequency is chosen to be considerably higher than the highest frequency of the frequency range of the process under study. The operation of the electronic accelerometer is reduced essentially to the following: under the action of acceleration the inertial mass is displaced, deforming the elastic suspension on which it is fastened. The displacement of the inertial mass, directly proportional to the magnitude of the acceleration being measured, is measured by an electronic indicator of small displacements, kinematically coupled with the inertial mass.

Fig. 13

Electronic accelerometers are made with an external and with an internal inertial mass. The diagram of an accelerometer of the first type, with a vibrotron \(^{8,14}\) as the indicator, is shown in Fig. 13. The inertial mass of the instrument is fastened directly to the vibrating rod \(1\) of the vibrotron. The elastic membrane \(2\) of the indicator plays the role of an elastic suspension for the inertial mass \(3\). The displacement limiter of the rod \(1\) is a rigidly fastened capillary tube \(4\), whose internal diameter slightly exceeds the diameter of the rod \(1\). In the gap between the inner surface of the capillary and the rod there is oil, held by capillary forces. The oil damps the oscillations of the rod \(1\). The sensitivity and the natural frequency of the accelerometer (with stable vibrotron parameters) depend on the magnitude of the inertial mass and the stiffness of its elastic suspension. Figure 14 shows the dependence of the sensitivity of an accelerometer with a vibrotron \(^{8}\) on frequency. As is evident from this characteristic, the sensitivity of the accelerometer rapidly falls with in-

by increasing the frequency. In the same figure, the dependence of the range of measured accelerations on frequency is shown by a dashed line.

In electronic accelerometers with an internal inertial mass[^9-12], the movable electrode of the electronic indicator is used as the inertial mass of the instrument. Among instruments of this type, the best known is the diode accelerometer with movable anodes. In it, on both sides of a flat heated cathode, flat anodes are mounted on elastic supports. Under the action of the component of acceleration normal to the plane of the anodes, the latter change their distance from the cathode, thereby changing the ratio of the currents to the anodes. Owing to their high current sensitivity, diode accelerometers operate directly into a magnetoelectric oscillograph, without preliminary amplification of the signals they produce[^12-16]. Diode accelerometers currently manufactured by the electrovacuum industry[^12,^16] for technical applications are made for several acceleration ranges, among which the most common are the ranges of \(10 g\) and \(100 g\). Figure 15 shows photographs of two accelerometers of this type.

Fig. 14.

Fig. 15.

Good results have been obtained when electronic accelerometers are used for semiautomatic and automatic monitoring of the unbalance of products under production conditions[^14]. In particular, the use of electronic accelerometers has facilitated the construction of automatic balancing machines for rotating parts for automatic lines[^14]. Figure 16 shows one of the electronic circuits of a balancing machine with an electronic acceleration indicator. Bearings 1 and 2, in which the part being checked rotates, are fastened on elastic supports 3 and 4. Therefore rotation of the part is accompanied by oscillations of the bearings and of the accelerometers 5 and 6 attached to them. The phase of the alternating current modulating the anode current of the accelerometer is determined by the position of the unbalance, and the amplitude of the alternating current by the magnitude of the unbalance.

Fig. 16.

The alternating current is separated from the constant component, filtered from interference produced by machine noise, and sent to the measuring device simultaneously with short pulses produced by commutator 7, connected to motor 8, which rotates the tested part 9. The position and magnitude of the unbalance can conveniently be read on the screen of an electronic oscilloscope connected into the circuit of a phase-pulse indicator. The alternating current of the accelerometer is fed to a phase shifter, from which a two-phase alternating voltage is taken to the deflecting plates of the electronic voltage, forcing the electron beam to rotate along a circle. The short voltage pulses supplied by commutator 7 are used to unlock the gated electron beam of the oscilloscope, which gives a bright spot 10 on the screen at the instants when the commutator contact closes. The distance of the spot from the center of the scale determines the magnitude of the unbalance, and the azimuth of the deflection determines the position of the unbalance.

Electronic accelerometers are also used for direct monitoring and recording of vibrations of tested products and machines under production conditions. The absence of the need to amplify the signals supplied by electronic accelerometers makes it possible to connect directly a large number of simultaneously operating electronic sensors to a multichannel oscilloscope.

Thus, for example, the use of electronic transducers made it possible to employ a 24-loop oscillograph easily under shop-floor conditions for the simultaneous recording of the vibrations of the tested article at 24 of its points[^6]. In particular, this apparatus was used for studies of vibrations of an aircraft fuselage under production conditions.

FORCE METERS

An electronic dynamometer consists of an elastic element, deformed by the measured force, and an electronic indicator of small displacements, which measures the magnitude of the deformation. An important advantage of electronic dynamometers is their high sensitivity, which permits direct reading of the monitored forces on a galvanometer, or their recording by means of a magnetoelectric or electronic oscillograph[^5],[^7],[^16]. Figure 17 gives several typical arrangements for installing small-displacement indicators in electric dynamometers. At the top is shown the arrangement of a device for measuring compressive forces. In the middle is the arrangement for installing an indicator to measure longitudinal forces stretching a rod. At the bottom is shown the arrangement for installing an indicator to measure torsional forces in a rod or in a shaft.

Another example of the application of electronic force meters is electronic tensometers[^5],[^7], which are end-type electronic micrometers used for measuring the length of the gauge base being monitored. For static measurements it is more advisable to use paired indicators operating in a bridge circuit, whereas for dynamic measurements less stable indicators, possessing greater sensitivity, may also be used.

Fig. 17.

Fig. 18.

Electronic dynamometers are used as the sensitive element of force meters operating in manufactured machines, devices used for monitoring the elastic properties of elastic parts, and fixtures serving for

measurements of the forces developed in the working members of machines during their operation. Fig. 18 shows the arrangement of a test setup\(^3\) for direct monitoring of the power developed on the shaft of the manufactured machine. The unbalance current of the bridge, into which a two-anode transducer is connected, is proportional to the torque applied to the shaft. This current enters one of the coils of wattmeter \(1\); to the second coil a current is directed from transducer \(2\) of the electric tachometer. The power developed by the machine under test is read directly from the wattmeter, calibrated in units of power.

Fig. 19.

Another example of the use of an electronic dynamometer in devices for product inspection is the direct observation of the reaction on the bearings of the monitored rotating parts during tests in the production process and during operation in the manufactured machine. The arrangement of such a device is shown in Fig. 19. At each of the bearings \(1\), in which the part under test rotates, electronic dynamometers \(2\) and \(3\) are installed in two perpendicular directions; they are connected to deflecting plates \(4\) of tube \(5\) of an electronic oscillograph. A two-phase alternating voltage, generated in coils \(6\) and \(7\) by permanent magnet \(8\), mounted on an axis connected with the rotating part under test, is applied to the same plates of the oscillograph.

ELECTRONIC MANOMETERS

Electronic manometers\(^7\) are also of considerable interest. The schematic diagram of one of them is shown in Fig. 20, \(a\). The pressure receiver is a sealed housing with an elastic membrane, whose deformation is measured by an electronic indicator of small displacements. An elastic bellows (a Vidi capsule or a Bourdon tube) may also serve as the sensitive element of the pressure receiver.

Fig. 20, \(b\) shows the arrangement of an electronic manometer whose membrane is the elastic wall of the indicator reservoir. The flat heated cathode \(1\) is located near anode \(2\), which performs the role of the membrane. Deformation of the anode is accompanied by a change in the current in the anode circuit of the indicator. Fig. 20, \(c\) shows the arrangement of an electronic manometer with an elastic body in the form of a bellows.

Considerable interest attaches to the use of electronic manometers for recording dynamic processes, as well as dynamic pressures arising in the testing of products. Thus, for example, the use of electronic manometers for monitoring the pressure inside the cylinder of an internal-combustion engine greatly simplifies the monitoring of the operation of engines being manufactured under production conditions. This is due to the fact that the high sensitivity of electronic manometers makes it possible to connect them directly to an oscillograph, without resorting to amplification of the signals supplied by them5–12.

Fig. 20.

It is also possible to use electronic manometers for monitoring the operation of other products, as well as for monitoring and regulating production processes according to the character of dynamic pressures observed with the aid of oscillographic devices5.

Of known interest, too, is the possibility of using low-inertia electronic manometers as receivers for ultrasonic flaw-detection apparatus4.

Finally, the use of electronic indicators of small displacements as the sensitive element of certain acoustic instruments is also of some interest6. In particular, highly sensitive microphones have been constructed by means of these indicators6. The sensitivity of these microphones is not inferior to that of carbon microphones at a noise level corresponding to the noise level of a good condenser microphone. Electronic microphones have good frequency characteristics, making it possible to use them for high-quality reproduction of speech and music.

CITED LITERATURE

1. L. Goncharskii, Elektrichestvo No. 6, 62 (1952).
2. L. Goncharskii, Elektrichestvo No. 12, 54 (1952).
3. L. Goncharskii, Elektrichestvo No. 7 (1953).
4. E. Bradchaw, Journ. of Sci. Instr. 22, No. 6, 112 (1945).

1. R. Gunn, Journ. of Appl. Mech. 7, No. 2, A-49 (1940).
2. H. Olson, Journ. of Acoust. Soc. of Am. 19, No. 2, 307 (1947).
3. G. Dion, Measures 17, No. 177, 95 (1952).
4. R. Lewis, Journ. of Acoust. Soc. of Am. 22, No. 3, 357 (1950).
5. W. Ramberg, Journ. of Res. Nat. Bur. of Stand. 37, No. 6, 391 (1946).
6. W. Ramberg, AIE Transactions 66, 735 (1947).
7. Electronic Eng. 22, 530 (1950).
8. V. Zeluff, Electronics 24, No. 2, 120 (1951).
9. Schottky, Ann. der Phys. 57, 541 (1918).
10. Harrison, Rev. of Sci. Instr. 19, No. 12, 936 (1948).
11. Wildback, Rev. of Sci. Instr. 18, No. 1, 67 (1947).
12. S. Levy, Exp. Stress. Analysis 9, No. 2, 151 (1952).
13. R. Widdington, Phil. Mag. 40, 634 (1920).