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Linear Variable Differential Transformer Signal Conditioning Circuit Based on Phase-Locked Loop
(2024-01-01)
Songsuwankit, Kanoknuch
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Petchmaneelumka, Wandee
;
Riewruja, Vanchai
;
Rerkratn, Apinai
The purpose of this paper is to propose a novel technique for extracting the position signal from an inductive displacement transducer named a linear variable differential transformer (LVDT). In general, the movement of the LVDT core causes its primary inductance change in linear form. The primary winding of the LVDT is used as a time-dependent element for the triangular and square wave generator, which can be called self-oscillation, to generate frequency. The advantage of the proposed technique is that it can measure the displacement using the LVDT without an external oscillator. The change in primary inductance causes the frequency deviation generated by the oscillator. The deviated frequency is captured and converted into a voltage signal using the principle of the phase-locked loop. All the components used in this study are commercially available. The merits of this proposed technique are simple configuration, small size, and low cost. Moreover, the operating range of the LVDT can be extended without the limitation of the nonlinear transfer characteristic. The performance of the proposed technique is discussed in detail and confirmed by experimental implementation. Experimental results show that the maximum error from the proposed technique is about 0.42% and the operating range of the LVDT can be extended to more than 200%. It can be seen that the proposed technique is suitable for embedded measurement in small or micro robots.
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Near Full Stroke Length Linear Range Enhancement Circuit for Linear Variable Differential Transformer (LVDT)
(2023-01-01)
Wisetphanichkij, Sompong
This paper proposes a linear range enhancement circuit for Linear Variable Differential Transformer (LVDT). The nonlinear is compensated with a signal obtained from an inverse hyperbolic tangent function circuit and with the appropriate gain settings within the circuit. The efficiency of the proposed circuit depends on the accuracy of the signal obtained by the inverse hyperbolic tangent function circuit. The simulation results with Pspice® program demonstrate the efficiency of the proposed circuit for enhancing the linear operating distance of the transducer. Under a relative error a(%) of 2.2%, the linear operating range is improved from ± 9mm to ± 35mm for LVDT Kn=250(kn=0.1) at ± 37mm full stroke length, which is much wider compared to the signal obtained from the transducer before the improvement.
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Low-Cost Linearity Range Enhancement for Linear Variable Differential Transformer
(2022-02-15)
Prommee, Pipat
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Angkeaw, Krit
;
Karawanich, Khunanon
This research proposes a low-cost and low-complexity technique to enhance the linearity range of linear variable differential transformer (LVDT) using logarithmic approximation and summing/subtracting operation. The proposed technique utilizes the feedforward approach and thus encounters no divide-by-zero behavior from inverse functions. The nonlinearity of LVDT can be counteracted by simply manipulating the parameters of the canceller circuit. Besides, the proposed technique can be applied to various LVDT nonlinearity types. The proposed linear enhancing circuit consists of operational amplifiers and a small number of passive elements. The nonlinearity cancellation could be further enhanced using a temperature-compensation circuit. Simulations were carried out using two different LVDT nonlinearity types: LVDT#1 and #2. The simulation results showed that the linearity enhancing circuit effectively enhances the LVDT linearity range, with the linearity errors of 0.51% and 1.83%, respectively. To validate, experiments were undertaken with the identical LVDT nonlinearity types using a circuit prototype, and the measured linearity errors are around 2.5% and 5.5%, respectively. The simulation and experimental results are agreeable with the theory, indicating that the proposed technique enhances the linearity range.
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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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Temperature Compensation for Transformer-type Transducer
(2021-01-01)
Songsuwankit, Kanoknuch
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Riewruja, Vanchai
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Watanachaturaporn, Pakorn
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Rerkratn, Apinai
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Petchmaneelumka, Wandee
A novel technique to compensate the temperature effect of a transformer-type transducer is proposed in this paper. The effect of the ambient temperature on the transformer-type transducer is investigated from a primary-winding current. The advantage of the proposed technique is that the temperature effect is compensated without requiring a temperature sensor, making it suitable for applications in robotic and automation systems operated in harsh environments. The primary-winding current of the transducer is generated using a second-generation current conveyor (CCII). The excitation signal of the transformer-type transducer is driven by the CCII and the current flowing through the primary winding is transferred to an output signal of the CCII. The deviation of the primary-winding current due to the temperature effect is evaluated from the output signal of the CCII. The temperature effect on the transducer is manipulated by a closed-loop principle using a subtract-and-sum action instead of a traditional proportional-plusintegral action to eliminate the deviation of the primary-winding current. Therefore, the temperature effect on the transducer is compensated. A linear variable differential transformer (LVDT) is used to demonstrate the proposed technique, whose performance is discussed in detail and confirmed experimentally. All devices used in this experiment are commercially available. Experimental results show that the measured error of the output signal from the LVDT at 70 C can be reduced from 6.2% without temperature compensation to 0.06% by using the proposed technique, which has the advantages of a low cost, simple configuration, and high performance.
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Position signal detector for linear variable differential transformer
(2020-12-01)
Rerkratn, Apinai
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Luangpol, Amata
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Petchmaneelumka, Wandee
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Riewruja, Vanchai
This paper presents the position signal detector for linear variable differential transformer (LVDT) based on RMS-to-DC converter. The proposed detector consists of the differential amplifier, the comparator, the phase detector, the controllable unity-gain inverting/non-inverting amplifier and the RMS-to-DC converter. The proposed technique provides a simple scheme and uses the low cost commercial available devices such as opamp, transistor and digital logic gate. The experimental testing with the commercial LVDT model OP12.5G from Solartron Metrology showing the proposed position signal detector can produce the output voltage corresponding to the measured displacement with satisfactory values and good linearity.
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Simple LVDT demodulator
(2020-10-13)
Rerkratn, Apinai
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Luangpol, Amata
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Riewruja, Vanchai
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Petchmaneelumka, Wandee
A simple technique to realize demodulator for linear variable differential transformer (LVDT) is presented in this paper. The proposed LVDT demodulator is based on sample and hold technique. The proposed scheme consists of peak detector, phase detector, monostable circuit, sample and hold circuit, and controllable unity-gain inverting/noninverting amplifier. The presented technique employs the simple and low-cost devices such as op-amp, and digital logic gate. Experimentation with the commercial LVDT model OP12.5G from Solartron metrology shows that the proposed LVDT demodulator provides the output voltage corresponding to the movement of LVDT core with satisfactory values and good linearity. The maximum error of the proposed demodulator is about 1.5%. In addition, the output magnitude of proposed LVDT demodulator can be adjusted by variable resistor (VR1) without the external circuit requirement.
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Linear-range extension for linear variable differential transformer using triangular signal
(2018-12-10)
Petchmaneelumka, W.
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Koodtalang, W.
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Songsuwankit, K.
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Riewruja, V.
This paper presents a linear range extension technique for the linear variable differential transformer (LVDT). The technique is based on a signal conditioning circuit using the analog lookup table, which provides very high resolution of resulting signal. The analog table which is obtained by the triangular signal generator, which has the frequency equal to the excitation frequency. Meanwhile, the referenced signal is obtained by the comparison between the excitation signal and the output signal of LVDT. It is used to synchronize with the triangular signal. The proposed technique is simply circuit configuration and it can be implemented using available commercial devices. The experiment shows that the performances of the proposed circuit can be extended from the normal operating range of LVDT to the maximum stroke range. In addition, the response time of the proposed techniques can be approximated as half period of the excitation signal.
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Compensation of Temperature Effect for LVDT Transducer
(2018-11-01)
Petchmaneelumka, W.
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Rerkratn, A.
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Luangpol, A.
;
Riewruja, V.
In this paper, a circuit technique to compensate the temperature effect in the output signal of the linear variable differential transformer (LVDT) is presented. The realization technique is based on the proposed feedback configuration to minimize the active component used in the circuit. The subtraction and sum schemes are provided instead of the error detector used in the traditional feedback loop. The feedback signal is obtained from two secondary winding signals of LVDT. The proposed feedback technique requires only the proportional control action to minimize the error caused by the variation of the ambient temperature. The sensitivity of LVDT is unaffected from the proposed compensation technique. The performances of the proposed technique are discussed in detail and confirmed by experimental implementation using the commercial devices. The maximum percentage error can be reduced from 6.52% of the LVDT output signal without temperature compensation to 0.05% of the proposed technique for the ambient temperature varied from 25°C to 70°C. The purpose of the proposed technique is emphasized in terms of high performance, simple configuration and low cost.
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Linear range extension for LVDT using analog lookup table
(2018-08-13)
Petchmaneelumka, W.
;
Koodtalang, W.
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Songsuwankit, K.
;
Riewruja, V.
A technique to extend the operating range of the linear variable differential transformer (LVDT) is presented in this article. The realization method is based on the analog lookup table achieved by the ramp signal generator where the frequency of ramp signal is equal to the excitation frequency. Therefore, the resolution of the resulting signal is very high. The output signals of the LVDT are provided to generate the reference signal to synchronize with the ramp signal. The proposed technique can extend the operating range of the LVDT from a normal operating range provided by the specification of the LVDT to maximum stroke range of the LVDT. The circuit of the proposed technique is simple and can be implemented using the commercial devices. The experimental results confirmed that the circuit performance are good agreement with the expected results. The response time of the proposed technique is about two periods of the excitation frequency.

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