RU1579231C - Method for determining nonlinearity of null-point accelerometer with compensating section - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: accelerometer metering axis is set in series in two relatively opposite positions in respect to free fall acceleration. Inverter is supplied with a.c. current and variations in values of d.c. output signal and phase shifts between disturbing a.c. current and inverter and load resistor currents are measured for two a.c. frequencies with integrating section and differentiating section or with differentiating section of reduced time constant disconnected. Nonlinearity coefficients for any frequency in working frequency band of accelerometer are found from known equations. EFFECT: enlarged frequency range for determining nonlinearity of accelerometer characteristic. 2 dwg

Description

 The invention relates to measuring equipment and can be used to control and adjust compensation accelerometers.

 The aim of the invention is to expand the frequency range for determining the nonlinearity of the characteristics of accelerometers.

 In FIG. 1 is a diagram of a compensation accelerometer explaining a method for determining non-linearity; figure 2 an example of the frequency response of the amplifier of the accelerometer with corrective links.

 A device that implements the proposed method contains a sensitive element 1 of the accelerometer with a position sensor 2 and a magnetoelectric transducer 3. The sensitive element 1 is covered by negative feedback through an amplifier 4. A load resistor 5 is connected to the output of the amplifier in the inverter 3 circuit, and a reverse resistor winding is connected through ballast resistor 6 is connected to a variable emf generator 7. In series with the inverse converter, an alternating current ammeter 8 is connected, and an alternating current ammeter 9 is connected to the output circuit of the amplifier. Parallel to the load resistor 5 and the inverse transducer 3 are connected, respectively, phase meters 10 and 11.

 When the compensation accelerometer is operating, the measured acceleration acting along the sensitivity axis deflects the sensor 1 of the accelerometer from the equilibrium position. This deviation is recorded by the position sensor 2, the signal from which through the amplifier 4 and the inverter 3 creates a moment equal to the moment acting on the sensor from the measured acceleration. Thus, the current in the inverter 3, and therefore the voltage across the load resistor 5, are proportional to the measured acceleration.

Compensation accelerometer inherent nonlinearity of the conversion of acceleration into output voltage. One of the causes of nonlinearity is the disturbing moment arising as a result of distortion of the magnetic field in the inverse transducer during the passage of current through its coil. The error in the measurement of acceleration as a result of the disturbing moment of the inverse transducer Δ a _{1 is} described by the expression
Δa ₁ = P ₂₁ a ² -P ₃₁ a ³ , where P ₂₁ , P _{31 are the} coefficients of the quadratic and cubic nonlinearities due to the disturbing moment;
but the measured acceleration.

Another reason causing the non-linearity of the accelerometer characteristic is the non-uniformity of magnetic induction in the gap of the inverter magnetic circuit. The error in the measurement of acceleration caused by the irregularity of the induction Δa ₂ obeys the expression
Δа ₂ = Р _2φ а ² + Р _3φ а ³ , where Р _2φ , Р _3φ are the coefficients of quadratic and cubic nonlinearities due to non-uniformity of magnetic induction.

 The influence of the nonlinearities of the accelerometer is manifested in the appearance of an error in the measurement of variable acceleration or in the measurement of constant acceleration when a variable component is superimposed on it. The frequency distortions inherent in the amplifier with corrective links make this error dependent on the frequency of the variable component of the measured acceleration.

To determine the nonlinearity in the accelerometer passband, the integrating link is turned off, the differentiating link is turned off, or its time constant is reduced. Disabling the corrective links makes the gain of the amplifier in the entire frequency range of the accelerometer constant and equal to K _about (see figure 2).

With the corrective links switched off, constant signals are measured at the accelerometer output for given in two opposite directions relative to the sensitivity axis of the gravity accelerations a _о and (-а _о ). An alternating current is supplied to the winding of the converter 3 from the EMF generator via a ballast resistor 6. The frequency of the generator 7 is set within the frequency band for which the gain of the amplifier is constant, for example, frequency f ₃ (see FIG. 2). The change in the constant signal of the accelerometer, caused by the supply of current to the inverter, is measured at accelerations a _о and (-а _о ). Phasometers 10 and 11 measure the phase shift θ ₁ between the current of the load resistor 5 and the current of the generator 7 and the phase shift θ ₂ between the currents of the inverter 3 and the generator 7. The alternating current components of the inverter and the load resistor are measured respectively with ammeters 8 and 9.

Set on the generator 7 a different frequency value within the bandwidth of the amplifier with a gain of K _about , for example, the frequency f ₄ (see Fig. 2). Similar to the previously performed measurements for the newly set frequency, the change in the constant signals of the accelerometer at accelerations a _о and (-а _о ), phase shifts Q ₁ and Q ₂ and the alternating current components of the inverter and load resistor are determined.

P₃₀₁=

P_20φ=

P_30φ=

где n₀=

n $\genfrac{}{}{0ex}{}{\text{1}}{\text{0}}$

n₁=

n₂=

G₃= ΔV₃(a_o)+ ΔV₃(-a_o);
G₄= ΔV₄(a_o)+ ΔV₄(-a_o);
G_-3=-ΔV₃(a_o)- ΔV₃(-a_o);
G_-4= ΔV₄(a_o)- ΔV₄(-a_o);
Ψ₃= θ₁₃+θ₂₃;
Ψ₄= θ₁₄+θ₂₄;
I_н3, I_н4 амплитуда тока нагрузочного резистора при частоте f₃ и f₄ соответственно;
I_оп3, I_оп4 амплитуда тока обратного преобразователя для частот f₃и f₄ соответственно;
К_I крутизна характеристики акселерометра;
ΔV₃(a_o),
ΔV₃(-a_o),
ΔV₄(a_o),
ΔV₄(-a_o) приращение постоянных сигналов на выходе акселерометра при действии ускорений а_о и (-а_о) и при подаче на обратный преобразователь переменного тока частотой f₃ и f₄ соответственно
θ₁₃, θ₁₄ сдвиг фаз между токами нагрузочного резистора и генератора при частотах f₃ и f₄ соответственно;
θ₂₃, θ₂₄ сдвиг фаз между токами обратного преобразователя и генератора при частотах f₃ и f₄ соответственно;
Коэффициенты нелинейности для акселерометра с подключенными корректирующими звеньями на любой частоте полосы пропускания акселерометра вычисляют по найденным вспомогательным коэффициентам в соответствии с выражениями
P_2fI=P_20I;
P_3f1= P

P_2fφ= P

P_3fφ= P

где Р_2fI, P_3f1 коэффициенты соответственно квадратичной и кубической нелинейностей, обусловленные возмущающим моментом, обратного преобразователя на частоте f;
P_2fφ,P_3fφ- коэффициенты соответственно квадратичной и кубической нелинейностей, обусловленные неравномерностью магнитной индукции, на частоте f;
К_f коэффициент усиления усилителя акселерометра на частоте f.Using the measurement results, auxiliary coefficients of quadratic and cubic nonlinearities are calculated for the accelerometer with the corrected links P _20I , P _30I , P _20φ , P _30φ in accordance with the expressions
P ₂₀₁ =

P ₃₀₁ =

P _20φ =

P _30φ =

where n ₀ =

n $\genfrac{}{}{0ex}{}{\text{1}}{\text{0}}$

n ₁ =

n ₂ =

G ₃ = ΔV ₃ (a _o ) + ΔV ₃ (-a _o );
G ₄ = ΔV ₄ (a _o ) + ΔV ₄ (-a _o );
G _-3 = -ΔV ₃ (a _o ) - ΔV ₃ (-a _o );
G _-4 = ΔV ₄ (a _o ) - ΔV ₄ (-a _o );
Ψ ₃ = θ ₁₃ + θ ₂₃ ;
Ψ ₄ = θ ₁₄ + θ ₂₄ ;
I _n3 , I _n4 the current amplitude of the load resistor at a frequency of f ₃ and f _4, respectively;
I _op3 , I _op4 current amplitude of the inverter for frequencies f ₃ and f _4, respectively;
K _I steepness of the accelerometer characteristics;
ΔV ₃ (a _o ),
ΔV ₃ (-a _o ),
ΔV ₄ (a _o ),
ΔV ₄ (-a _o ) the increment of constant signals at the output of the accelerometer under the action of accelerations a _o and (-a _o ) and when applied to the inverse AC converter with a frequency of f ₃ and f ₄ respectively
θ ₁₃ , θ ₁₄ phase shift between the currents of the load resistor and the generator at frequencies f ₃ and f ₄ respectively;
θ ₂₃ , θ _{24 the} phase shift between the currents of the inverter and generator at frequencies f ₃ and f ₄ respectively;
The nonlinearity coefficients for the accelerometer with the corrective links connected at any frequency of the accelerometer passband are calculated from the found auxiliary coefficients in accordance with the expressions
P _2fI = P _20I ;
P _3f1 = P

P _2fφ = P

P _3fφ = P

where P _2fI , P _{3f1 are the} coefficients of the quadratic and cubic nonlinearities, respectively, due to the disturbing moment of the inverse transducer at frequency f;
P _2fφ , P _3fφ are the coefficients of the quadratic and cubic nonlinearities, respectively, due to the non-uniformity of magnetic induction, at a frequency f;
To _f the gain of the accelerometer amplifier at a frequency f.

 Thus, the nonlinearity of the accelerometer is determined within its working frequency band.

Claims (1)

A METHOD FOR DETERMINING THE NONLINEARITY OF A COMPENSATION ACCELEROMETER WITH CORRECTIVE LINKS, consisting in the fact that the measuring axis of the accelerometer is installed sequentially in two opposite directions relative to the acceleration of gravity, an alternating current is supplied to the inverse converter, and measurements of changes in the direct output frequency of the current at two different values phase shifts between disturbing alternating current and inverter currents and load about the resistor, calculate the coefficients of quadratic and cubic nonlinearities, characterized in that, in order to expand the frequency range for determining nonlinearity, the integrating link is turned off before installation, the differentiating link is turned off or its time constant is reduced, two AC frequencies are set through the inverter in the frequency bandwidth amplifier with disabled corrective links with a constant gain K _about measure the alternating currents of the inverter and load resistor, in relation to the inverter current and load resistor currents and changes in the constant output signal of the accelerometer, auxiliary coefficients of quadratic and cubic nonlinearities caused by the disturbing moment of the inverse transducer and uneven magnetic induction are determined, and the nonlinearity coefficients at any frequency of the accelerometer passband are calculated in accordance with the expressions

P _{2 f I} P _{2 0 I}

where P _2fφ , P _{3fφ are the} coefficients of the quadratic and cubic nonlinearities, respectively, due to the non-uniformity of magnetic induction, at a frequency f;
P _{2 f i} , p _{3 f i the} coefficients of the quadratic and cubic nonlinearities, respectively, due to the disturbing moment of the inverse transducer, at a frequency f;
P _20φ , P _{30φ are the} coefficients of quadratic and cubic nonlinearities, respectively, due to uneven magnetic induction in the passband of the amplifier frequencies with corrective links disabled;
P _{2 0 i} , P _{3 0 i are the} coefficients of the quadratic and cubic nonlinearities, respectively, due to the disturbing moment of the inverter in the passband of the amplifier frequencies with the corrective links disabled;
K _about the gain of the amplifier in the passband of frequencies with disabled corrective links;
K _f the gain of the accelerometer amplifier at a frequency f.

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