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Linear Range Enhancement Circuit for LVDT based on Bipolar OTA with Relative Error Control
(2022-01-01)
Wisetphanichkij, Sompong
This paper proposes a Linear Range Enhancement Circuit for Linear Variable Differential Transformer (L VDT) which was by inverse hyperbolic tangent function implemented by bipolar type OTA. The proposed circuit requires only 2 OpAmps, a bipolar-type OTA and a small number of passive elements. Furthermore, the mathematical models were used in the analysis to determine the configuration methods of the circuit to improve the linearity range enhancement techniques under controlled maximum relative error (%). Two configuration methods of relative error are 0% at center with flat top and ripple top with specific maximum relative error. The Pspice simulation results show the efficiency of the proposed technique for widening the linear operating displacement of the transducer up to 30mm for LVDT (ks = 50 v/m, and kn = 0.2) for 1 % of maximum relative error.
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A temperature-compensation technique for improving resolver accuracy
(2021-09-01)
Petchmaneelumka, Wandee
;
Riewruja, Vanchai
;
Songsuwankit, Kanoknuch
;
Rerkratn, Apinai
Variation in the ambient temperature deteriorates the accuracy of a resolver. In this paper, a temperature-compensation technique is introduced to improve resolver accuracy. The ambient temperature causes deviations in the resolver signal; therefore, the disturbed signal is investigated through the change in current in the primary winding of the resolver. For the proposed technique, the primary winding of the resolver is driven by a class-AB output stage of an operational amplifier (opamp), where the primary winding current forms part of the supply current of the opamp. The opamp supply-current sensing technique is used to extract the primary winding current. The error of the resolver signal due to temperature variations is directly evaluated from the supply current of the opamp. Therefore, the proposed technique does not require a temperature-sensitive device. Using the proposed technique, the error of the resolver signal when the ambient temperature increases to 70 °C can be minimized from 1.463% without temperature compensation to 0.017% with temperature compensation. The performance of the proposed technique is discussed in detail and is confirmed by experimental implementation using commercial devices. The results show that the proposed circuit can compensate for wide variations in ambient temperature.
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Linear-range extension for linear variable differential transformer using binomial series
(2020-01-01)
Petchmaneelumka, Wandee
;
Songsuwankit, Kanoknuch
;
Tongcharoen, Jakkapun
;
Riewruja, Vanchai
The linear-range extension technique for a linear variable differential transformer (LVDT) is described in this paper. Generally, the LVDT has a narrow linear operating range caused by its nonlinear transfer characteristic. To extend the linear operating range, the nonlinear behavior of the LVDT must be adjusted. In this paper, the circuit building block providing the LVDT inverse transfer characteristic using binomial series approximation is proposed for linearizing the nonlinear behavior of the LVDT. The third-order inverse transfer characteristic of the LVDT is synthesized from analog multipliers and a difference amplifier comprising an operational amplifier (opamp). All active devices used in this study are commercially available. Therefore, the attraction of the proposed technique is in the simple configuration and low cost, making it suitable for an embedded measurement system. The performance of the proposed technique is discussed in detail. Simulation and experimental results confirming the performance are also included. As a result, the linear range of the commercial LVDT used in this study can be extended more than 500%. The full scale error of the measured value is about 0.23% over the entire operating range.
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High-accuracy resolver-to-linear signal converter
(2018-09-02)
Petchmaneelumka, W.
;
Mano, P.
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Songsuwankit, K.
;
Riewruja, V.
A high-accuracy resolver-to-linear signal converter for the measurement of angular displacement is proposed in this paper. The proposed converter comprises two sections: a demodulator and linear shaper. In the first section, the demodulator makes use of the sample-and-hold circuit (SHC) to sample the peak amplitude of the resolver signal. The control signal of the SHC is provided from the resolver signals instead of the excitation signal used in traditional approaches. The proposed demodulator requires no analogue multiplier and low-pass filter. Therefore, the fast response time of the proposed demodulator is achieved. In the second section, the linear shaper consists of the inverse-sine function scheme together with a switched-gain amplifier to produce the linear signal proportional to the shaft angle. The hyperbolic tangent characteristic of the operational transconductance amplifier is utilised to realise the inverse-sine function scheme. The proposed technique requires one phase of the resolver signal to obtain the linear signal. Therefore, the position error caused by amplitude imbalance between the two resolver signals is avoided. The performances of the proposed converter are discussed in detail and demonstrated by an experimental implementation using commercial devices. The experimental results show that the maximum relative error and response time for the excitation frequency of 3 kHz are measured as 0.06% and 0.11 ms, respectively.
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Linear variable differential transformer temperature compensation technique
(2018-01-01)
Petchmaneelumka, Wandee
;
Mano, Pitsini
;
Riewruja, Vanchai
A feedback technique to compensate for the temperature effect on the output signal of the linear variable differential transformer (LVDT) without losing the sensitivity is presented in this paper. The proposed technique is based on the use of a voltage-controlled amplifier to scale the amplitude of the excitation signal for temperature compensation. The proposed feedback technique provides the proportional-plus-integral control action to minimize the error caused by the temperature variation. The proportional-plus-integral action is realized using the integral scheme in the proposed technique. The peak amplitude of the LVDT output signal is sampled by the sample-and-hold circuit (SHC) to obtain the feedback and displacement signals, where the control signal of the SHC is provided by the LVDT output signal. The proposed LVDT temperature compensation technique is emphasized in terms of simple configuration and low cost. Note that the proposed technique is suitable for signal conditioners embedded in smart sensors and smart materials. The performance of the proposed technique is confirmed by experimental implementation using commercially available devices. The maximum error of the core displacement signal can be reduced from 6.52% for the uncompensated scheme to 0.098% for the compensated scheme at the ambient temperature of 70 °C.

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