Rerkratn Apinai, Tongcharoen Jakkapun, Petchmaneelumka Wandee, Riewruja Vanchai
School of Engineering, King Mongkut's Institute of Technology Ladkrabang, Ladkrabang, Bangkok 10520, Thailand.
Sensors (Basel). 2022 May 12;22(10):3674. doi: 10.3390/s22103674.
In this paper, a circuit technique to extend the measuring range of a linear variable differential transformer (LVDT) is proposed. The transfer characteristic of the LVDT contains the odd function form of the cubic polynomial. Therefore, the measuring range of a commercial LVDT is linear in a narrow range compared to its physical dimensions. The wide measuring range of the LVDT requires a large structure of the LVDT, which increases the scale and the cost of the measurement system. The measuring range of the LVDT can be linearly extended to the maximum of the stroke range using the proposed technique. The realization of the proposed technique is based on the use of the hyperbolic sine (sinh) function of the electronic circuit building block, named the class AB bipolar amplifier. The class AB bipolar amplifier can be obtained by the current feedback operational amplifier (CFOA). The circuit of the proposed technique requires two CFOAs and an operational transconductance amplifier (OTA) as the active devices and all devices used in the proposed technique to synthesize the sinh function are commercially available. The proposed technique exhibits an ability to compensate for the nonlinear characteristic of the LVDT without digital components. The proposed technique is attractive in terms of its simple circuit configuration, small size, and low cost. The linear range extension of the LVDT used in this paper is significantly increased with a maximum error of about 18.3 μm of 6.2 mm at the full stroke range or the full-scale percentage error of about 0.295%. The results indicate that the proposed technique provides excellent performance to extend the measuring range of the LVDT without modifying the LVDT structure.
本文提出了一种扩展线性可变差动变压器（LVDT）测量范围的电路技术。LVDT的传递特性包含三次多项式的奇函数形式。因此，与其实物尺寸相比，商用LVDT的测量范围在较窄范围内呈线性。LVDT的宽测量范围需要LVDT具有较大的结构，这会增加测量系统的规模和成本。利用所提出的技术，LVDT的测量范围可以线性扩展到行程范围的最大值。所提出技术的实现基于使用电子电路模块的双曲正弦（sinh）函数，即AB类双极放大器。AB类双极放大器可通过电流反馈运算放大器（CFOA）获得。所提出技术的电路需要两个CFOA和一个运算跨导放大器（OTA）作为有源器件，并且所提出技术中用于合成sinh函数的所有器件都是市售的。所提出的技术具有无需数字元件即可补偿LVDT非线性特性的能力。所提出的技术在电路配置简单、尺寸小和成本低方面具有吸引力。本文中使用的LVDT的线性范围扩展显著增加，在全行程范围6.2mm时最大误差约为18.3μm，或满量程百分比误差约为0.295%。结果表明，所提出的技术在不修改LVDT结构的情况下，为扩展LVDT的测量范围提供了优异的性能。
