~ t ~ = rn~ �9 . 1 0 0 % .

HI o

Figure 2 shows the dependence of A,Jz on the relative speed F = f/fmax-

For 0.05~F<0.75 , A~ does not exceed • and in the range most fully examined, which J

is indicated by the dashed line, a,n on average is not more than 0.008%, while the standard deviation is So(Am) • %.

The spread in the readings does not exceed • which corresponds to the maker's claims, and shows that one can use the flowmeter as a working one, or as a substandard means of measuring the flow of natural gas if it is individually calibrated.

LITERATURE CITED

i. All-Union State Standard 8.369-79: The State System of Measurements: the State Primary Standard and All-Union Test Scheme for Means of Measuring Gas Mass Flow Rates in the Range 4"10 -2 to 2.5"102 kg/sec [in Russian].

2. V.V. Sychev et al., Thermodynamic Parameters of Air [in Russian], Izd. Standartov, Mos- cow (1978).

AUTOMATED SYSTEM FOR TESTING DYNAMIC CHARACTERISTICS

OF GAS FLOW SENSORS

M. M. Grigor'ev, V. V. Kuz'min, V. M. Loskutov, V. M. Mezhuev, and A. V. Fafurin

UDC 532.526.4

Industrial requirements make it necessary to measure time-varying liquid and gas flows b~ means of standard facilities. Particular importance attaches to the metrological aspects related to dynamic tests and calibration for nonstationary working conditions.

Traditional flowmeter calibration systems, which may include equipment of the highest accuracy available at the All-Union Flowmeter Research Institute, are not suitable for these purposes because they do not provide for measuring precisely the instantaneous values of the input quantities.

Here we describe a computerized system (Fig. i) for performing dynamic tests on gas flow- meters, which involves determining the response functions for the primary sensors to harmonic flow oscillations. There is a closed aerodynamic loop, whicb works with diagnostic facilities and a data-acquisition system DAS.

The air is supplied through the filter I by the high-pressure VVD-160M blower 2 with output 0.15 kg/sec at 7 kPa. The harmonic oscillation at frequency f is provided by the rota- ting disk slide Ii: <Q>=Q(l+~cos2=f0.

Slide valves 4, 6, and 7 enable one to regulate the mean flow rate Q smoothly together with the oscillation amplitude 6. The positions of slide valves 4, 6, and 7 are controlled by MPK-131-5 microdrives 5 from the control panel CP. To prevent vibration being transmitted to the equipment from the blower, the apparatus and the blower are connected by the flexible rubber tube 3. To provide uniform velocity patterns, the inlet to the working system is provided with a forechamber 8 and nozzle i0, whose shape is a Vitoshinskii curve. The fore- chamber is equipped with grids 17 and honeycombs 9.

Uniform rotation in the disk slide ii is provided by a special drive fitted with an elec- tromechanical stabilization system. The dc motor 22 is coupled to the slide ii through the flexible clutch 19 and reduction gear 18, transfer ratio 1:12. The motor shaft bears the gear ring 21, which acts as a chopper. As it rotates, the magnetic head 20 produces a pulse

Translated from Izmeritel'naya Tekhnika, No. ii, pp. 46-48, November, 1989.

1094 0543-1972/89/3211-1094512.50 �9 1990 Plenum Publishing Corporation

J

Fig. 1

train, which passes to the speed stabilizer 23, which provides for smooth speed adjustment for the slide Ii over the range 0.i-i0 Hz and maintains it at a set level with an error of not more than 0.1%.

The motor speed is monitored by the Ch3-34A frequency meter 24. To determine the ini- tial phase, the shaft for the slide ii bears the permanent magnet 15. When the ring 16 ro- tates, the magnet closes the normally opened contacts in a relay at a strictly defined instant, which provides a level one control signal corresponding to the initial phase angle.

The data-acquisition system handles the measurements as it includes the set of measuring instruments MI working with the fast sensors in the DAS (Fig. i). The instantaneous speeds in nonstationary turbulent flows are measured by four thermoanemometers made by the Donets University, type TA-15, which work with miniature sensors. The TA thermoanemometer employs one-filament, two-filament, and three-filament sensors and can measure correspondingly one, two, or three components of the instantaneous velocity vector in the circular tube 12 and working part of the flow converter 13.

Pulsating static pressures are measured at the wall of the flow channels by amplifying pressure converters APD, which work in conjunction with miniature inductive differen- tial pressure sensors type DMI-0,1-2.

The DAS employs a two-level circuit. At the first level, there is the 15IPG computing suite based on an Elektronika DZ-28 microcomputer and an independent tape store type ES-9002, while at the upper level, there is an ES 1045 (see the structural diagram in Fig. 2).

The output signals from the MI pass via normalizing converters NC previously adjusted to the working ranges of the analog-digital converters ADC type F7077/I, which are from -i to +i V. The ADC in each case quantizes the input signal in level witha step of 1 mV every 8 p s e c .

The microcomputer controls the ADC via the interface unit IUl, which consists of the switching control SC and synchronizing unit SU. SC provides synchronous operation for all four ADC on command. When the digitization is complete, the SC transfers the data byte by byte to the memory.

The synchronization unit provides real-time operation. The data acquisition is syn- chronized with the oscillation phases by the marker pulse from the reed relay 14 and the synchronizing pulses SP, which are produced by the motor speed stabilizer 23 (Fig. 1). In a single rotation of the shaft in motor 22, the magnetic head 20 produces 80 pulses, which corresponds to the number of the teeth on the gearwheel 21. With a transfer ratio of 1:12

1095

M~

J Fig. 2

in the reduction gear 18, there are thus 960 synchronizing pulses produced in one turn of the slide ii by unit 23, or 480 pulses during one period in the flow pulsation.

The key panel on the SU enables one to set the number of samples K per period, with K - 1 a multiple of 480. When the program is started, IU l awaits the marker signal, and on the first synchronizing pulse triggers the ADC and inputs the data to the microcomputer. The next ADC triggering is when the SU counter has received a certain number of synchron- izing pulses. The interval between samples is A~=2~/K--L .

OS VT MKhTI Fortran is used for the microcomputer programs, which enables one to process the data and output the results to the thermal printer TP. If it is necessary to process large data volumes, the input data can be passed through IU 2 from the microcomputer to the ES-9002 independent store. The tape may be processed in that case by an ES-I045 computer on programs written in Assembler and Fortran.

To provide reliable rates averaged over the ensembles, the averaging should be per- formed on N = i000 periods:

in which j = i, .... K. The error arising from averaging over a finite number of realizations then [2] should not exceed o=e! V~, in which e = 0.03 is the maximum intensity of the tur- bulent speed pulsations. Similarly, one determines the pressures < p > and the errors in measuring them. The overall errors in measuring the velocities < u > and pressures < p >, with allowance for the errors in the measuring instruments, normalizing converters, and ADC, and the errors due to averaging over finite numbers of realizations, do not exceed 3 and 2% cor- respondingly.

One can measure velocity profiles < u > (r) by displacing the thermoanemometer sensor along the radius r over several cross sections by means of a micrometer mechanism providing a reading accuracy of i 0.005 mm. The profiles are used in calculating the volume flow rates

R

corresponding to the oscillation phases < Q > = 2~f < u > rdr , in which R is tube radius. 0

Tests on dynamic characteristics made with this equipment have shown that the reliabil- ity is high and the system is convenient to use.

LITERATURE CITED

i. A.S. Livshits et al., A Two-Level Data-Acquisition Suite for Use with Nonstationary Turbulent Flows [in Russian], Dep. VINITI No. 5286-V-87, 22 July (1987).

2. J.S. Bendat and A. G. Piersol, Engineering Applications of Correction and Spectral Analysis, Wiley (1980).

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