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Pt 100
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This study details the design of a digital instrument for precise temperature measurement using a Pt100 sensor. It covers signal conditioning with a quarter deflection bridge and differential amplifier, implementing cascade linearization to correct non-linearities. A LabView-based virtual instrument incorporates a second-order Butterworth low-pass digital filter, derived via bilinear transformation, to effectively remove frequency-controlled noise. The system digitizes analog signals, processes them to achieve accurate temperature readings, and provides robust noise reduction, crucial for reliable industrial and academic applications. Key aspects include optimal sampling rate selection and comprehensive digital signal processing for enhanced measurement fidelity.
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- A digital instrument was designed using LabView for precise temperature measurement from a Pt100 sensor.
- The system incorporates a conditioning circuit (quarter deflection bridge and differential amplifier) to convert the sensor's resistance change into an analog voltage signal.
- A National Instruments data acquisition card (DAQ) with 16-bit precision (0-100°C range, 61.2µV resolution) is used for Analog-to-Digital Conversion (ADC).
- Digital Signal Processing (DSP) is applied to enhance signal manageability and information extraction.
- The Pt100 sensor's temperature-resistance relationship (quadratic) introduces non-linearity, which is corrected using a cascade linearization algorithm. The 'exact' inverse function was chosen over an approximation due to better accuracy at higher temperatures.
- An Anti-Aliasing Filter is crucial before ADC to prevent information loss due to sampling frequencies below the Nyquist-Shannon threshold.
- A second-order Butterworth low-pass digital filter was implemented via bilinear transformation to remove specific frequency-controlled noise.
- The filter coefficients were determined for a cut-off frequency of 15Hz and a sampling rate of 200Hz, chosen to balance accuracy with the slow-changing nature of temperature.
- A virtual instrument (VI) in LabView provides a user-friendly interface for simulating temperature signals, injecting noise, applying DSP, and saving processed data in '.csv' format.
- The efficacy of the filter is demonstrated through spectral analysis (Fourier Transform, DFT, FFT), showing significant attenuation of noise components (e.g., near 50Hz).
- Key advantages of DSP include independence from physical component aging, while a disadvantage is information loss due to signal discretization.
- The overall system successfully linearizes the sensor output and effectively reduces noise, achieving high measurement fidelity.
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