RU2018900C1 - Method of testing and diagnostics of pneumohydraulic systems - Google Patents

Abstract

FIELD: pneumohydraulic system diagnostics. SUBSTANCE: method comprises steps of measuring state parameters of an object in all testing points, main and additional, over 2-4 testing cycles; forming threshold values of correlated characteristics of units of the object according to values of parameters, measured at first 2-4 cycles; at further period of testing process measuring parameters only in two-three testing points of the object, checking state of the object by comparison of values of measured parameters with their threshold values; determining the object as suitable one, when the measured values are in limits of the threshold values, at opposite case performing diagnostics process for localizing a damage, that is performing searching of a damaged unit by successive registration of parameters, allowing to calculate a correlated characteristics of a separate unit; comparing the correlated characteristics of each unit, had been calculated according to measured parameters, with their threshold values, had been formed at first cycles. EFFECT: enhanced reliability, lowered time period of damage localization for well known methods of testing and diagnostics. 1 cl, 1 tbl, 2 dwg

Description

 The invention relates to technical cybernetics, is intended for automated monitoring and diagnostics of the state of pneumohydraulic systems of power plants.

 A known method of monitoring and diagnosing the state of an object, which consists in measuring the parameters at all control points and comparing them with threshold values [1].

 The disadvantage of this method is the need to process a significant amount of information on measurements at all control points of the object and the associated long localization of failure.

 There is also a known method for monitoring and diagnosing a pneumohydraulic object, which means that the parameters are measured cyclically at the control points of the object, they are compared with the calculated threshold values, and when they go beyond the threshold values, the parameters are measured, generalized characteristics of the pneumohydraulic units are calculated from them at additional control points, completing the object, and compare them with threshold values of the generalized characteristics, localizing the failure [2]. This method is adopted as a prototype.

 According to the known method, from all the sensors installed on the object, the readings of a limited number of sensors (at control points) are first recorded to decide on the state of the object ("norm" or "abnormality"). A limit on the number of control sensors is introduced at the stage of designing an object using mathematical modeling of all possible malfunctions of the object and choosing the most informative parameters. The decision on the results of the control is made by comparing the measured values of the parameters with their threshold values. In the event that any of the measured parameters exceeds the threshold values, a decision is made about the "abnormality" of the object, the parameters are measured at additional control points, the generalized characteristics of the object nodes are calculated from them, and the failed node whose characteristic is beyond its threshold values is determined.

 Under the generalized characteristic of the node is understood such a characteristic that allows you to most fully determine its condition. For example, for a centrifugal pump, such a characteristic is a pressure characteristic, for local hydraulic resistance it is a resistance coefficient or effective area of the flow area.

 The threshold values of the generalized characteristics of the known method are calculated taking into account possible technological deviations and measurement errors. This leads to an unjustified expansion of the calculated threshold values of the characteristics, which leads to an unjustified expansion of the calculated threshold values of the characteristics, which leads to a decrease in the sensitivity and reliability of the method and increases the localization time of the malfunction.

 The aim of the invention is to increase the reliability and sensitivity of recognition and reduce the time of localization of failure.

 This is achieved by pre-measuring the parameters at the main and additional control points of the object, determining the (real) threshold values of the generalized characteristics of the pneumohydraulic units, which are used for signaling a failure.

 The positive effect when using the proposed method lies in the fact that the real threshold values of the generalized characteristics formed by the new method have a much smaller spread than the threshold values obtained by the known method by calculation, since the deviations of the parameters due to the limit technological tolerances on manufacturing and marginal error of measurement are excluded. This allows you to increase the reliability and sensitivity of recognition and reduce the time of localization of the failure.

In FIG. 1 shows a fragment of a complex hydraulic system, where SC is a centrifugal pump, 1,2,3, ..., i are nodes of the hydraulic circuit, measured parameters: P ₁ , ..., P _i are pressure, Q _i is flow rate, n - pump speed, T - fluid temperature; figure 2 shows a block diagram of a prototype device for implementing the proposed method, where 1 is a control object, 2 is an analog-code converter, 3 is a first threshold value generator, 4 is a threshold value corrector, 5 is a first comparison unit, 6 - a second threshold value generator, 7 — a decisive unit, 8 — a second comparison unit, 9 — a registration unit, 10 — a control unit.

(1) где ρ (Т ) - плотность перекачиваемой жидкости, для гидравлического сопротивления коэффициент гидравлического сопротивления
Y

=

(2)
Пороговые значения Y_iмакс и Y_iмин по известному способу определялись по зависимостям
Y_{i макс}=Y_iном+

+ΔY_{i пульс}
(3)
Y_{i мин} =Y_iном-

-ΔY_{i пульс},
(4) где Δ Y_{i изг} - отклонение обобщенной характеристики, обусловленное технологическими допусками на изготовление;
Δ Y_{i изм} - отклонение обобщенной характеристики, обусловленное погрешностью измерения;
Δ Y_{i ном} - номинальное значение обобщенной характеристики;
Δ Y_{i пульс} - отклонение обобщенной характеристики, обусловленное пульсациями.The generalized characteristics of the nodes making up the object, allowing to determine its state, are for the SC pressure characteristic
Y _us =

(1) where ρ (Т) is the density of the pumped liquid; for hydraulic resistance, the coefficient of hydraulic resistance
Y

=

(2)
The threshold values of Y _imax and Y _imin by a known method were determined by the dependencies
Y _{i max} = Y _in +

+ ΔY _{i pulse}
(3)
Y _{i min} = Y _inom -

-ΔY _{i pulse}
(4) where Δ Y _{i izg} - deviation of the generalized characteristics, due to technological manufacturing tolerances;
Δ Y _{i ISM} - deviation of the generalized characteristics due to measurement error;
Δ Y _{i nom} - nominal value of the generalized characteristics;
Δ Y _{i pulse} is the deviation of the generalized characteristic due to pulsations.

According to the proposed method, the threshold values of the generalized characteristics of the nodes are formed according to the dependencies
Y _{i max} = Y _{i fact} + Δ Y _{i pulse} ; (5)
Y _{i min} = Y _{i fact} - Δ Y _{i pulse} , (6) where Y _{i fact} - the real value of the node characteristics.

(7)
Реальные характеристики узла определяются в первых тактах контроля по зависимостям
для насоса
Y_факт=

(8)
для гидравлического сопротивления

(9) где К - число первых циклов измерения параметров во всех точках, т.е. величину К выбирают в зависимости от динамических характеристик объекта (обычно К=5...10 циклов).Thus, due to the implementation of the proposed method, the tolerance on threshold values is reduced by
±

(7)
The real characteristics of the node are determined in the first measures of control by dependencies
for pump
Y _fact =

(8)
for hydraulic resistance

(9) where K is the number of first cycles of parameter measurement at all points, i.e. K value is selected depending on the dynamic characteristics of the object (usually K = 5 ... 10 cycles).

 The essence of the proposed method consists in the following sequence of operations.

During the first K cycles, the parameters are measured at all the main and additional control points of the object. Compare the measured values of the parameters of the control points with threshold values. When the measured parameters are within the threshold values, the "norm" of the object is recorded. The values of the measured parameters form the real values of the characteristics of each node and pump according to formulas (8) and (9). Form real threshold values of the generalized characteristics according to formulas (5) and (6). Remember the real threshold values of the generalized characteristics of all nodes. In the future, only a limited number of parameters are measured at control points and the state of the object is monitored by comparing the measured parameters with threshold values (registration at the other points is not performed). When the threshold values of one of the parameters are exceeded, measurements are taken at additional points. According to dependences (1) and (2), the values of the characteristics of the nodes of the object are calculated. Consistently compare the calculated values of the characteristics of all nodes calculated by formulas (1) and (2) with the real ones until they find a node with Y _i > Y _{i max} or Yi <Y _{i min} .

 Consider an example implementation of the method as applied to a hydraulic system with a screw centrifugal pump, a fragment of which is shown in figure 1.

At the stage of system design, the pressures P ₃ and P _{i + 1} , which are the most informative for a given list of possible malfunctioning states, were chosen as the measured parameters. As the permissible limits of these parameters P ₃ and P _{i + 1} when testing the object were set respectively 100 ^. 10 ⁵ ± 3 xx 10 ⁵ Pa and 40 ^. 10 ⁵ ± 10 ⁵ Pa.

In the first control cycle the following parameters were measured: P ₁ = 5x x10 ⁵ Pa, Q _i = 4,10 ^-2 m ³ / s, T = ²⁰ ° C, P ₂ = 3,9 ˙10 ⁵ Pa, P ₃ = 98 ˙ 10 ⁵ Pa, P ₄ = 83 ˙ 10 ⁵ Pa, P _i-1 = = 53 ˙ 10 ⁵ Pa, P _i = 43.4 ˙ 10 ⁵ Pa, P _{i + 1} = 38.6 x x ^{10 5} Pa

A comparison of the measured parameters P ₃ and P _{i + 1} with threshold values allowed us to register the normal state of the object, since
97 ˙ 10 ⁵ <98 ˙ 10 ⁵ <103 ˙ 10 ⁵
37 ˙ 10 ⁵ <38.6 ˙ 10 ⁵ <43 ˙ 10 ⁵ .

 According to the measured parameters of the object, the values of the actual generalized characteristics of the nodes, which are given in the table (row 1), were calculated by formulas (8) and (9).

Taking into account the parameters fluctuations measured in the first steps of the control, the changes in the hydraulic characteristics of the nodes (Y _pulse ) were calculated and the threshold values of the real (real) characteristics of the nodes (lines 3 and 4 of the table) were formed from dependences (5) and (6). These threshold values of the generalized characteristics of the nodes were stored for use in the event of a malfunction.

In the future, the operation of the object was carried out with the measurement of only the parameters P ₃ and P _{i + 1} , the values of which were compared with acceptable limits. The remaining parameters (Q, T, n, P ₁ , P ₂ ... P _i ) were not recorded.

At a time T _k , an exit beyond the lower limit was recorded, first of parameter P ₃ , and then of parameter P _{i + 1} . This served as the basis for fixing the abnormal state of the object and connecting all other parameters of the object. At the time T _{k1, the} average values of the measured parameters were: P ₁ = 5 ˙ 10 ⁵ Pa, Q _i = 4 ˙ 10 ^-2 m ³ / s; Т = 20 ^о С, Р ₂ = 3 ˙ 10 ⁵ Pa, Р ₃ = 93 ˙ 10 ⁵ Pa, Р ₄ = 78x x10 ⁵ Pa, Р _i-1 = 48 ˙ 10 ⁵ Pa, Р _i = 38,4 ˙ 10 ⁵ Pa, P _{i + 1} = 33.6 ˙ 10 ⁵ Pa.

Based on the measured values, the values Y _{avar of the} actual characteristics of the nodes at the time T _k1 were again calculated (row 5 of the table).

 A consistent comparison of the actual generalized characteristics of the nodes with their threshold values showed that the cause of the object's malfunction was a decrease in the pressure of the SC due to its cavitation due to a decrease in pressure at the inlet of the SC with an increase in the hydraulic resistance (clogging) of assembly 1 (filter).

Application of the proposed method allowed to reduce the tolerance by the pressure head of the SC by more than 20 times, eliminating the measurement error and technological spread (Y _max - Y _min according to the proposed method is 0.1 kJ / kg, while according to the known method it is 2.08 kJ / kg).

 Reducing the tolerance allows you to increase the reliability and sensitivity of recognition and for developing faults to reduce the recognition time.

 Implementation of the proposed method by the device is as follows.

From the first generator 3 of the threshold values at the command of the control unit 10, the sensor code of the first measured parameter P _{3 is} output to the analog-code converter _2. The value of the measured parameter is entered in the first comparison unit 5, where the values of the upper and lower threshold values of the parameter P are entered from the generator 3 ₃ . In block 5 of the comparison, the comparison operation P _3min , P _3ism , P _3max . Similarly, the measurement and verification of the parameter P _{i + 1} .

When the measured parameters P ₃ and P _{i + 1 are found} in the number at the command of the control unit 10 from the second driver 6 of the threshold values, the sensor address codes are issued to the converter 2 of the analog code, the readings of which are necessary to calculate the characteristics of the first node of the object (P ₁ , Q _i , P ₂ ). The values of these parameters are recorded sequentially in the decision block 7, where the value of the generalized characteristics of the node 1 is calculated according to the dependence (2). Similarly, the characteristic of the SC is calculated (according to the parameters P ₂ , P ₃ , T and equation 1) and all the nodes of the object.

The described process is repeated K times for all nodes of the pneumohydraulic object, and using the expressions (5), (6), (8), (9), the threshold values of the characteristics of the nodes are calculated. From the decision block 7, the generated threshold values of the generalized characteristics of all nodes Y _{i max} and Y _{i min} are entered in the memory of the second threshold driver 6.

Further, at the command of the control unit 5, the device switches to measuring parameters only at control points, i.e. in P ₃ and P _{i + 1} . If in the future any measured parameter after the comparison is not normal, then an error signal appears at the output of the first comparison unit 5. According to this signal, the control unit 10 issues a command to the second threshold value generator 6, which alternately enters the addresses of the sensors P ₁ , P ₂ and Q _{i of the} first node into the analog-code converter 2. These parameters are measured, and then their values are sent to the decisive block 7. Calculation is performed according to dependence (2) (or according to dependence (1) in the case of SC). The calculated value Y _{i is} entered in the second comparison unit 8, where the upper and lower threshold values Y _{i max} and Y _{i min} , which were earlier generated in the first K cycles, are received simultaneously by the commands of the control unit 10 from the second threshold driver 6. Are compared, and if the setting is correct, then from the second former six thresholds in the analog-to-code converter recorded addresses these sensors measuring P _2, P ₃ and T (for SC). The described process is repeated for the SC and for all nodes of the chain.

If the parameter Y _i is not normal, then in the second comparison unit 8, an interrupt signal is generated for the process of calculating the values of the node characteristics, by the command of the control unit 10, the number of the faulty node and the type of malfunction are recorded in the display unit 9. This completes the operation of the device.

Claims (1)

 METHOD FOR MONITORING AND DIAGNOSTIC OF A PNEUMAHYDRAULIC OBJECT, which consists in cyclically measuring the parameters at the control points of the object, comparing them with the calculated threshold values and measuring them beyond the threshold values, measuring the parameters at additional control points, calculating generalized characteristics of the pneumohydraulic units for all measured parameters, constituting the object, and compare them with the threshold values of the generalized characteristics of the pneumohydraulic units, localizing the failure, distinguishing In order to increase the reliability and sensitivity of the method and reduce the time of failure localization, the parameters are preliminarily measured at the main and additional control points, the real threshold values of the generalized characteristics of the pneumohydraulic units making up the object, which are used to localize the failure, are determined from the measured parameter values.

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