Wheatstone bridge configuration. is the temperature sensor and determines the temperature range in absolute measurements. When differential measurements are needed is substituted by another temperature sensor. and are set to .
Wheatstone bridge sensitivity when using a NTC thermistor (solid trace) and a PRTD (dashed trace). .
Wheatstone bridge NET level when using a NTC thermistor and a PRTD. The latter is already above the requirement (4) and, therefore, it is discarded. This is valid for all the frequency range. The power dissipated in the temperature sensor is .
Drive bridge circuit scheme for the square wave bridge supply.
Bridge and MUX connections. This configuration allows absolute (using different scales) and differential measurements. From 0 to 5: reference resistors. From 6 to 9: temperature sensors.
IA noise equivalent circuit.
NET for the IA at different temperatures. The observed discontinuities are caused by the different references, , used at each temperature scale. .
Sallen-Key Butterworth LPF to avoid aliasing due to high-frequency noise and interference signals.
Analog and digital processing measurement chain. The digital processing consists, basically, of a decimator and a subsequent difference averaging that results in a digital demodulation.
(Color online) Expected NET at (for a single channel) before (dash trace) and after (solid trace) the digital processing. The modulation and demodulation technique results on a quasiflat spectrum from dc to .
Theoretical FEE global TC, , assuming worst-case conditions.
(Color online) Thermal insulator design concept including sensor placement principle. A total amount of eight sensors and a high-stability resistor are attached to the metal core of the aluminum.
(Color online) Frequency response of the thermal insulator (solid trace), , along (for comparison) with a first-order LPF with the same cutoff frequency, . An estimation of the frequency response of the thermistor wires, , is also plotted (dash trace). The latter limits the temperature fluctuations of the FEE and wires to at .
(Color online) Power spectral density in terms of equivalent temperature for the first run of measurements. Power dissipated in the NTC, , is . For further details see text.
(Color online) Power spectral density in terms of equivalent temperature for absolute (iii) and differential (v) temperature measurements. The theoretical spectral density estimation (iv) has been calculated using Eq. (36) and the FEE (ii) and ambient (i) temperature spectral densities. .
Summary of theoretical noise level at and digital parameters involved in the demodulation process.
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