Sensors & Instrumentation Systemmx.nthu.edu.tw/~yucsu/3271/09.pdf · Sensors & Instrumentation System ESS3271 Lecture Variable area capacitor Reed switch LVDT Linear potentiometer

Sensors & Instrumentation System

ESS3271 Lecture

Variable area capacitor

Reed switch

LVDT

Linear potentiometer

Experimental Setup

• A linear assembly moves in either direction, left or right, by manually turning the scaled control

• One complete revolution of the scale moves the linear assembly 1 mm

• The devices available are– A linear scale– A variable area capacitor– A reed switch– A linear variable differential transformer– A linear potentiometer …

LVDTLinear variable differential transformer

Soft iron

Reed Switch

Experiments

• 1. Linear variable differential transformer (LVDT)• 2. Variable area capacitance• 3. Reed switch• 4. Linear potentiometer• 5. Four-bit optical encoder

Investigate the variable properties of LVDT

Investigate the differential properties of LVDT

Experimental Results

Linear measurement with LVDT

Phase-Sensitive Detection

• Require a frequency reference• Typically an experiment is excited at a fixed frequency

and the lock-in detects the response from the experiment at the reference frequency


• Amplify the signal and then multiply it by the lock-in reference using a phase-sensitive detector or multiplier

• The output of the PSD is two AC signals


• If the output is passed through a low pass filter, the AC signals are removed

• If wr equals wL, the difference frequency component will be a DC signal and the filtered output will be


Variable capacitor with or without gain

Reed switch


Linear potentiometer


Four-bit optical encoder (D/A conversion)



實驗原理

– LVDT + Reed Switch相關問題

– 請比較 LVDT、Variable area capacitance 和Linear potentiometer的實驗結果，並說明這三種方式各自的優缺點。(準確度、靈敏度、線性度、適用範圍、、、)

–請分析LVDT實驗誤差的來源與大小。

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Sensors & Instrumentation Systemmx.nthu.edu.tw/~yucsu/3271/09.pdf · Sensors & Instrumentation System ESS3271 Lecture Variable area capacitor Reed switch LVDT Linear potentiometer

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