ME CHANICAL MEASUREMENTS

MOBILE HYDRAULIC REFERENCE DYNAMOMETRIC INSTALLATION

B. N. Ivanov, A. Ya. Lyubarskii, E. Ya. Varivoda, and M. V. Lukina

UDC 531.2.089.68

Dynamometric instruments and testing equipment are at present being checked disjointedly (in accordance with the type of equipment), and much time is being spent delivering the work- ing instruments (dynamometers, dynamometric transducers) to the state and departmental test- ing services and supplying reference instruments (grade 3 dynamometers, hardness standards, etc.) to the stationary installations (test machines, presses, hardness testers). Electrical strain gauges are widely used for measuring force and weight. They have to be tested ~n s~u, since the secondary instruments and connecting cables of these transducers are in- stalled in a stationary manner.

One way to improve the state metrological inspection system is through producing mobile test laboratories ~TLs) which are suitable for testing the equipment used in measuring quan- tities with similar or approaching physical properties. In this case it is advisable to com- bine in a single MTL the testing of dynamometric instruments, testing machines, and hardness- measuring instruments. This is dictated by the established measuring-equipment nomenclature, according to which the above equipment is classified as intended for determining the mechani- cal characteristics of materials, and to the established structure of testing departments.

The most promising testing method consists of measuring ~n 8~tu, since in this case the need for delivering instruments to the testing organization is eliminated and the requirement of a spare stock of instruments can be dispensed with. The above measuring-equipment group is also characterized by a second advantage, namely that the testing Of stationary testing ma- chines and hardness testers requires the sending of testers with portable instruments who can simultaneously test the entire range of equipment, employing more fully the working time of testers and eliminating the expenditure on sending parts of instruments to the testing organization.

It is advisable to equip the MTLs with sets of portable reference instruments for check- ing testing machines up to 500 kN, presses, impact testers, hardness testers, and mobile reference dynamometers used for testing working dynamometers of the largest standard sizes.

The overwhelming majority of testing instruments which can be used in an MTL as testing equipment are mass produced by our enterprises (e.g., grade 3 reference dynamometers made ac- cording to the All-Union State Standard (GOST) 9500-75, grade 4 reference weights made ac- cording to GOST 12656-67, table balances with weights made according to GOST 13882-68, sets of hardness testers made according to GOST 9013-75, surface-roughness specimens made accord- ing to GOST 9370-75, standard instruments for linear and angular measurements, etc.).

The chief difficulty in producing MTLs consists of the present lack of mass-produced dynamometric installations which meet all the requirements specified for the MTLs. Thus, the utilization of level dynamometers [i, 2] is made difficult owing to the wear of knife-edged bearings due to shaking in the course of transportation; the type DOG-20 machines [3] have acceptable overall dimensions and sufficient precision, but they are complex in use, pollute the MTL with leaking liquids, and have a very large mass.

In this connection the Ukrainian Center of Standardization and Metrology (UkrTsSM) is producing an installation with a measurement error not exceeding 0.2% and based on a hydrau- lic dynamometer.

The possibility of producing hydraulic membrane dynamometers with a floating charge from a pump and an error not exceeding 0.1% was indicated in [4]. However, the application of a pump installation for the floating charge complicates the MTL design and utilization.

Dynamometers based on elastic membranes are more suitable for mobile dynamometric in- stallations. How~Ter, existing transducers of such a type [5] have an insufficiently large measurement range and a considerable hysteresis error.

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 43-45, February, 1981.

0543-1972/81/2402-0115507.50 �9 1981 Plenum Publishing Corporation 115

The UkrTsSM has proposed a new type of membrane strengthened with steel wires on its external surface [6]. The wire ends are encased in metal ferrules which transmit the effort directly to the force-transducer casing. This makes it possible to raise the upper measure- ment limit by a factor of 3-5 and to produce a hydraulic dynamometer with a simple construc- tion not requiring a floating charge. This dynamometer was used as a basis for developing an experimental dynamometric installation [7] with small overall dimensions and mass, as well as a precision which meets the requirements specified for MTL installations.

A schematic of the reference mobile dynamometric installation (RMDI) is shown in Fig. i. Its main unit consists of the frame I, the hydraulic dynamometer 6-9, and the loading mecha- nism 18-21. The frame consists of the stand 4, as well as the Upper 5 and lower 20 crossbars. The upper crossbar 5 carries the hydraulic dynamometer, whereas the lower one carries the loading mechanism.

The foundation has three supports (one hinged support and two adjustable in height), thus making it possible to set the frame in a vertical position by means of the incorporated level when the RMDI is being prepared for operation.

The hydraulic dynamometer consists of its casing 6, the rigid center 8~ and the membrane 7, which form the enclosed cavity 9 filled with liquid. This cavity is connected to the free- piston manometer which consists of the sleeve 13 and the piston 12 with the disk I0 rotated by means of an electric motor. The initial position of the piston 12 is marked with the index ii. The hydraulic-dynamometer casing 6 is connected to the rods 14 which carry the mobile cross-member 15. Its height can be adjusted by means of the regulating nuts 16. The rods 14 are provided with the springs 17 which serve to produce preliminary pressure in the cavity 9.

The RMDI loading mechanism comprises the screw 18, the level 19, and the reverser 21. The tensile dynamometer 2 is placed in the course of testing between the lugs of the cross- member 15 and the lower plate of the reverser 21, whereas the compression dynamometer 3 is placed between the cross-member 15 and the upper crossbar of the reverser 21.

The tensile dynamometer 2 is placed in the course of certification between the cross- member 15 and the lower plate of the reverser 21, whereas the compression dynamometer 3 is placed between the cross-member 15 and the upper plate of the reverser. Before the tested dynamometer is loaded, the hydraulic dynamometer is balanced by means of the preliminary ten- sioning of the springs 17 so that the pressure developed by the hydraulic dynamometer is balanced by that produced by the free-piston manometer and due to the mass of the piston 12 and the disk i0. The piston 12 then floats to its initial position and the mark comes opposite the index ii. Next the disk lO is loaded with weights corresponding to the first loading stage and the dynamometer loading is produced by rotating the screw 18 until the piston 12 with its load floats up to a position when the marker coincides with the index ii. Such loading is continued up to the tested-dynamometer upper measurement level, when the weights are removed in turn and inversed reduction loading is produced. The particular fea- ture of the hydraulic dynamometer (Fig. 2) consists of the utilization of the rolling-over membrane i, consisting of the reinforcing and packing layers 2 and 3, respectively. The re- inforcing layer 2 (Fig. 2b) is made from 0.15-mm steel brass-coated wires radiating from the center of the hydraulic dynamometer. The packing layer 3 is made from natural raw rubber, thus providing a better adhesion to the surface of the reinforcing-layer wires. The mem- brane 1 edges are pinched between the rigid center 4 and the compression ring 5 on the inner side of the dynamometer and between the casing 9 and the compression ring 8 on its outer side. The pinching is made in such a manner that the relnforclng-layer wires are fastened separately from those of the packing layer. Hydraulic sealing is attained by press- ing the packing layer to the surface of the casing and the rigid center. The reinforcing- layer wires are fastened in two ways as shown in Figs. 2c and 2d. In the first case the ends of wires are held in the crimper i0 between the compression ring and casing surfaces, whereas in the second case the ends of wires are twisted around the ring ii and held in the crimper 12.

Under the effect of the initial pressure and the elastic forces of the reinforcing and packing layers the free part of the membrane assumes the shape of half a torus.

When the measured force P is applied to the pistons, a proportional pressure is produced in the hydraulic-dynamometer cavity and measured by the free-piston manometer. The piston is displaced as the result of the partial compressibility of the liquid and its bleeding into

116

8 g f- kJ

P; 4 56 , ~ = ~ ~ F - - - : . - - - ~ ,,, ',, B .,'-

T o the f r ee -p i s ton m a n o m e t e r a

f

The cross s ec t i on is nomina l l y expanded onto a p lane

b

6

/

�9

c /-~?/ d

Fig, ! Fig. 2

the manometer. The membrane i is then rolled over the cylindrical guiding surfaces 6 and 7 by the compression rings 5 and 8 without changing the shape of its free portion or its effec- tive area. The membrane 1 contacts with the surfaces 6 and 7 by means of the reinforcing layer 2 wires without any relative sliding or shift of the latter and it does not produce any noticeable hysteresis error, whereas the tensile effort is transmitted to the casing and the piston directly through the reinforcing wires.

The fact that the reinforcing layer is located on the surface of the membrane which is fixed by means of the protruding wire-ends serves to transmit the tensile loading and the thrusting effort due to the liquid pressure through the reinforcing wires without connecting to the effort-transmitting circuit the elastic packing layer of the membrane. This makes it possible to raise the tolerated pressure and reduce the hysteresis error. Moreover, the density of the reinforcing wires' location is raised as compared with their location inside the elastic layer, and this also helps to raise the tolerated pressure and, thereforeD in- crease the maximum force measured by =he hydraulic dynamometer. Other valuable properties of the hydraulic dynamometer with a rolling-over membrane consist of its mobile-part self-center- ing property and its insensitivity to skewing, thus making it possible to design a simple RMDI arrangement without forward-movement guides and to avoid errors due to friction in the guides.

The basic error sources of the above dynamometer consist of the friction losses produced when the membrane is rolled over (including rolling friction of the reinforcing layer and deformations of the membrane), changes in the effective area of the membrane when it is rolled over, ambient temperature variationsj etc.

Since, in accordance with the published data [8]~ it is very difficult to calculate the effect of all the factors on the measurement preoision, the latter has been evaluated experi- mentally by means of a direct loading machine and a set of reference weights.

In the course of investigations we determined the error in measuring the effort when the dynamometers were compressed with forces up to 50 kN.

The observation results were processed in accordance with the recommendations of [9~ I0]. All the computations were based on the assumption that the observation results are subject to the normal distribution law (this is confirmed by the data obtained in accordance with [9]).

The total measurement error did not exceed 0.6% for the resulting flducial probability of 0.97. The difference in readings obtained in loading and unloading of the dynamometer did not exceed 0.01%,

117

These results lead to the conclusion ~hat the measurement error falls within the range tolerated for reference grade 1 dynamometric equipment [ii].

It should be noted, however, that in order to mass produce the hydraulic dynamometer developed by the UkrTsSM, it is necessary to produce special tooling for manufacturing the rolling-over membrane.

LITERATURE CITED

i. V. I. Kirnosov, Measurement of the Mechanical Properties of Materials [in Russian], Standartov, Moscow (1976).

2. G. N. Leonov, Metrologiya, No. 12 (1975). 3. M. K. Zhakhovskii, Techniques for Measuring Pressure and Rarefaction [in Russian],

Standartov, Moscow (1952). 4. A. S. Akobdzhonyan, Hydraulic Systems for Measuring Efforts [in Russian], Mashinostroe-

nie, Moscow (1972). 5. V. I. Vodyanik, Elastic Membranes [in Russian], Mashinostroenie, Moscow (1974). 6. A. Ya. Lyubarskii, Inventor's Certificate No. 579546, Byull. Izobr., No. 41 (1977). 7. A. Ya. Lyubarskii et al., Inventor's Certificate No. 735943, Byull. Izobr., No. 19

(1980). 8. M. M. Reznikovskii and A. I. Lukomskaya, Mechanical Testing of Raw and Processed Rubber

[in Russian], Khimiya, Moscow (1968). 9. All-Union State Standard (GOST) 8.207-76: "State System for Ensuring Uniform Measurements

(GSI). Direct measurements with repeated observations. Methods for processing observa- tion results. Basic regulations" (1976).

i0. V. I. Pronenko and R. V. Yakirin, Metrology in Industry [in Russian], Tekhnika, Kiev (1979).

ii. GOST 8.066-73: "GSI. All-Union Testing Scheme for dynamometric equipment" (1973).

IMPROVED REFERENCE ELECTROMAGNETIC FLOWMETER TYPE ERO-I

A. K. Kaviev, R. G. Gazizov, V. I. Aksenov, and A. V. Pavlov

UDC 681.121.031.22.089.68

The flowmeter type ERO-I described in [i] is intended for testing working flowmeters and measuring the flow of conducting liquids under laboratory conditions. It is produced in three standard models which differ from one another by their measured-flow ranges and flow transducers. The ERO-I measuring device consists of adc digital voltmeter. The flowmeter effective error does not exceed 0.5%.

Below we examine ways for improving the ERO-I flowmeter by extending the range of its application and increasing the convenience of its utilization by automating its measuring process on the basis of up-to-date digital techniques.

Figure 1 shows a functional schematic of the improved flowmeter which comprises the pri- mary transducer i; the modulator 2; the adder 3; the analog-to-digital converter (ADC) 4; the digital counter 5; and the indicator 6. The problem of picking out the signal from inter- ference is solved by means of orthogonalization. The modulation frequency (orthogonalization) is set below 50 Hz, which serves to suppress almost completely the electromagnetic interference at frequencies which are multiples of the main frequency.

The modulated analog signal is fed to the adder 3 whose output signal is transmitted to the ADC 4, which operates with a unitary code, thus making it possible to assemble the adder from electronic counters capable of functioning also as storage cells. Next the signal is fed to the digital counter 5, which forms in combination with the ADC 4 a low-frequency digital filter, thus providing minimal phase distortions (as distinct from analog filters).

The ERO-I flowmeter can operate in two conditions, namely, with a "rotating" and a con- stant magnetic field. The application of two series connected flow-transducers, one of which operates with a constant magnetic field and is used for measurements, makes it possible to

Translated from Izmeritel'naya Tekhnlka, No. 2, p. 46, February, 1981.

118 0543-1972/81/2402-0118507.50 �9 1981 Plenum Publishing Corporation