Golovina Anastasiya

General rising of problem

      The account systems of  heat become necessary, to both the users of heat and his suppliers. By the primary quality criterion of the serve systems of  heat temperature absence discomfort in an apartment and permanent presence of hot water with a certain temperature in a necessary volume. It is arrived at due to introduction of autonomous boiler rooms which function on principle of complete automation technological process. Important advantage of the decentralizing serve systems of  heat  is possibility  the local adjusting in the systems of the housing heating and hot water–supply. However much exploitation of source of warmth and all of complex of ancillaries of the housing system of serve of  heat inhabitants not always enables to a full degree to utillize this advantage. The last researches rotined [1]that  a necessity of control of defervescence is on every floor, not to attract repair–operating organization for maintenance of sources of serve of  heat , introduce  floors ultrasonic worm flowmeter, for operative surveillance after defervescences in building.

Rising of research tasks

      Presently there are different devices and checking of expense of water and heat systems. They have a row of failings outweigh  in particular high error of measuring. This problem in autonomous boiler rooms it is possible to untie by the use of ultrasonic, that work on principle of change of time–of–flight ultrasonic signal from a source to the receiver of signals, which depends on a flowrate liquid. There is a task of choice of amount and correct location of worm flowmeter on every floor, with subsequent integration of device which is developed, to the general structure of automation.

Decision of the put task and results of researches

      Most proper simple flowmeter, which for today is a device which measures the expense of heat and temperature on an entrance and output object of heat transfer. (figure 1).

Fugure 1 – Heating system of building

      Amount of warmth, brought to the body or taken from him, it is possible to define his masses after the known values, specific heat capacity and after the change of temperature.

      In the flowmeter value of difference of enthalpy in direct and reverse  streams integrated at times. Equalization looks like for his work:

Q = qC(t1 – t2),                                                          (1)

where Q –is an amount of warmth which is selected or taken in; С – coolant heat capacity, kJ / kgK; t1 – coolant temperature in the supply pipeline, deg. K; t2 – coolant temperature in the return pipeline, deg. K.

      The error of expense measuring of heat depends both on the error of temperature measuring and from the error of measuring charges of serve of  heat , which depend on exactness of primary measurings transformers (sensors of temperature and flowmeter serve of  heat ). Also with exactness of determination of parameters of serve of  heat  metrology descriptions of entrance scaling strengtheners, exemplary resistors, parameters of ACP are CPLD the most direct rank. The particle of error is brought in by calculable part. Limitation on exactness of mathematical operations in an eventual device and not quite correct algorithms can fully ruin ideal entrance part of worm flowmeter  even.

      There is a problem of choice of method. In every case an or user, or competent installations, must estimate all of dignities and failings each of methods and to do an optimum choice taking into account possibilities of user. Two last types of devices (vortical and mechanical) are foremost oriented to such user which wishes to purchase worm flowmeter   on a minimum cost and for which high metrology descriptions in the wide range of measurings of not principles. If speech goes about a device with high metrology descriptions in more wide range of measuring, apply worm flowmeter, built on the base of electromagnetic transformers of expense. Will estimate the error of the various  measurings.

Error estimation of measuring result of energy resources

      Metrology descriptions of worm flowmeter   are determined calculation methods on descriptions of those measurings knots, devices and systems which meters are built on the base of. Complication in the estimate of errors is explained external of such devices environments, necessity of account of variable composition and physical properties of worm flowmeter  (presence of admixtures), and and others like that. Will consider the estimation of error of result of measuring of energy supply, which is based on a method which is executed  in [5].

      At the account of warmth a result of measurings of енергоресурсів used (released) for some time domain is the accumulated sum of n of intermediate results of measurings, determined as:

S = Σ(x_iΔt_i),                                                                (2)

where x_i –is an instantaneous value of і result of measurings of instantaneous expense (amounts of енергоресурсів are in time unit), Δt_i – is duration of  і time domain.

     A task is put thus: to estimate the error of result of S of account of energy resources on condition that the error of mean of measurings is rationed as limits of relative, that is assumed relative δ_Дor the resulted γ_Д error.

      For simplification of calculations without the decline of community will assume that Δt_i =Δt = const. Then

S = Δt Σx_i.                                                                (3)

      Will conduct the estimation of error of result of S of account of energy in supposition, that every result of measurings of x_i contains some error, actual value of εto which can be presented the sum of systematic ε_sys casual ε_cas of constituents.

      Possibly also, that the casual constituent error of ε_cas has an even function of closeness (worse case) and expected value, even a zero. From the last supposition at n, to aspiring to endlessness, it follows that a casual constituent will not do errors influence on the result of S of account of energy.

      Will assume farther, that the results of measurings x_i are evenly up–diffused from initial x_н to eventual x_к of values in the range of measurings.

      Passing from a sum to the integral and taking into account the systematic constituent of error, obsessed:

                                        (4)

or

S = Δt·n·S₁,                                                               (5)

where

                                             (6)

      Taking into account that the systematic constituent of error on the range of measurings can be presented a sum three constituents: additive ε_а, multiplicative η_м and nonlinearε_н(х), that

                                                (7)

that

                                   (8)

      As a result of integration obsessed:

                          (9)

      The first addition of expression presents the basic value of result of measurings:

                                                        (10)

and that three are additions is an actual value of absolute error:

                                  (11)

      Taking into account that адитивна and multiplicative component errors determine the parameters of line which approximates dependence of error after the range of transformations

                                              (12)

      Consequently, the actual value of absolute error of result of measurings is evened:

                                                (13)

that makes in relative units:

                                                          (14)

      After the substitution of ε_s and S_1н in the last expression obsessed:

                              (15)

      Thus, relative error of result of measurings of S₁, and, consequently, and to the result of S of account of енергоресурсів, determined expression:

                                              (16)

      Will conduct the subsequent reasonings for two cases: setting of norms of error  as limits of resulted, that is assumed γ_д and relative δ_д error.

      1. At setting of norms of error   as limits of γ_дof the resulted error which is assumed, the module of actual value of absolute error  is limited the limit of Δ_д = = γ_д (x_к – х_н) of absolute error which is assumed:

                                              (17)

      Possibly, that

                                                     (18)

where k - is a coefficient which determines the weight of systematic constituent in the error , the values of him lie in a range from a zero to unit.

      Then in a limit

                                                (19)

      Will assume farther, that

                                        (20)

where k_а и k_м — accordingly coefficients which determine the weight of additive and multiplicative constituents of error in the systematic error of measuring.

      In the total

                  (21)

that after substitutions and transformations gives final expression in a kind :

                                   (22)

      2. At setting of norms of error  as limits of δ_д of relative error which is assumed, the module of actual value of absolute error  is limited the limit of Δ_дof absolute error which is assumed.

      Reasoning like, it is possible to rotin that limit of relative error of result of account of energy of, which is assumed, makes:

                                              (23)

      Got expressions allow to estimate the relative error of result of S of account of energy resources at the set limits of relative, that is assumed relative δ_д or the resulted γ_д error instantaneous expense of energy.

      According to this method were calculated, the results are listed in table 1:

Table 1 - Comparative description after the class of exactness of different methods

Method	The limits of permissible error	Measurement range
Electromagnetic flowmeters	±1–2%	1:500 1:1000
Ultrasonic Flowmeters	±2%	1:500 1:1000
Vortex	–5,5%	1:200

      Moreover, for electromagnetic flowmeters are specified fairly significant deficiencies: decrease of accuracy in sticking of precipitation on the surface, the destabilization of the meter (zero offset, the appearance of systematic errors, etc.) because of stray currents on pipelines, inability to work on an autonomous power source " . For the ultrasonic flow mentioned only one drawback: the need for long straight sections before and after instrumentation to align the homogeneity of coolant flow. But in practice, these "long" holdings are only 50-100 cm! It is hard to believe that in 99,9% of the heat objects not found extra 1,5 m to install the heat from the tangent. At the same time in the same report noted: "Abroad, in the most developed European countries, which are widely used ultrasonic devices. This is a high quality coolant, the internal surface of pipes used in heat distribution and rejection of TSC. It is unlikely that Ukraine can be attributed to "the most developed European countries with distilled and polished coolant pipes, however, is currently on a number of Ukrainian energy companies are installing predominantly ultrasonic Heat" best foreign heat meters, which cost exceeds the value of domestic samples 2-3 times are the limits of relative error ±2 % in the range of measurements coolant flow 1:100. At the same time, "the vast majority of domestic manufacturers have limits of relative error ±2 % flow measurements in the range 1:200, more than two dozen heat registers, registered in the Register of measuring instruments, are the limits of error in flow measurement range of 1:500 or even 1:1000! ".

      To solve the problem analyzed functional features of autonomous boiler-rise building and designed the structure of the instrument taking into account the required number of Heat on each floor. Multilevel structure as planned further integration developed the device in the overall structure of automation. When placing the piezoelectric tube outside of the acoustic energy reflected from the surface pipe-liquid and is distributed in the form of acoustic vibrations in the pipe wall. In this form, both longitudinal and transverse waves. The latter can reach the receiver piezoelectric acoustic oscillations before passing through the liquid. To eliminate this proposed placing piezoelements from different sides flange, fitted with non-metallic gasket. Amplitude А_Р, and phase φ_Р reverberation waves differ from the amplitude A and phase φ fundamental wave. Receiving pezoelement perceives the resulting oscillations, with amplitude А_П and phase φ_П. The result is a phase shift Δφ_Р = φ_П – φ, particularly troublesome for the existing flow. To this shift was small, it should be А_Р < 0,01А. In addition a reverberation impulse can disfigure front basic an impulse and prematurely to include a frequency chart. For this exception it is suggested to move workings impulses in relation to represented by an electronic delay line.

      In all of flowmeter as sensors for measuring of temperature are utillized standard thermometers of resistance.

      Together with the transferred advantages, there is  a row of problems which require additional research, namely:

• maintaining the technical and operational performance over time;
• high accuracy measurement over a wide dynamic range;
• absence of moving and acting in the flow measuring element;
  no loss of pressure;
• independence of the testimony of the changes in the electrical environment;
• low power;
• the possibility of non-contact measurement of liquids;
• opportunity to measure the flow of liquids in a wide range of nominal bore diameter pipelines (15 ... 1600 mm);
• possibility of a simple simulation calibration without dismantling the primary converter with pipeline.

      Also, there are several issues that require serious consideration, namely:

      - for acoustic flow :

• operation of ultrasonic transducers in the presence of asymmetrical profiles change of speed, as well as work at small Reynolds numbers Re;

• need to consider depending on the speed of sound on the physico-chemical properties of various measurement environments;

• presence of parasitic acoustic signals;

• asymmetry of electron-acoustic channels.

      The presence of these factors brings application over in ultrasonic flowmeter of the special methods and facilities of indemnification to the necessity, to the use of differential charts of measuring for the selection of "weak" useful signal.

      -for resistance thermometers:

• uneven temperature distribution over the cross termoresiever;

• heating of termoresiever measuring current;

• thermal inertia of termoresiever.

      To improve the signal / noise propagation time of ultrasonic signal is often measured in two directions, both pezokristall operate alternately receivers, the transmitters. This can be implemented using the switch device shown in fig. 2, which works with a relatively low frequency (400 Hz). Sinusoidal ultrasonic waves (with a frequency around 3 MHz) are transmitted in a pulse mode with the same slow clock frequency (400 Hz). Adopted RF signals transmitted from behind for a time T. The value of this delay depends on the rate of flow. Time T is measured using the TOF detector, and a synchronous detector is used to determine the time difference T spent on signal propagation along and against the current flow. This ultrasonic sensor has a sufficiently high accuracy, its zero drift is 5·10^–3 m/s² during 4-hour interval.

Figure 2 – Scheme of an ultrasonic flowmeter, in which each crystal plays a role, and the transmitter and receiver

Figure 3 - The principle of ultrasonic sensors. Flash-animation, 75 frames,
looped repetition,7kb

Conclusions

      1. The analysis of descriptions of errors of the probed methods  of water flowmeter conducted in–process with metrology descriptions and limits of possible error, Ukraine taken from national standards allowed to define that an ultrasonic method is more precisely from all of other and DSTU answers.

      2. The structure of device of control of expense of amount of heat is developed with the set degree of exactness, which will watch the expense of water and defervescence on every floor. A device will be realized by setting on the floors of height house of ultrasonic of water flowmeter.

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