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Thermal diagnostics front-end electronics for LISA Pathfinder
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Image of FIG. 1.
FIG. 1.

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 .

Image of FIG. 2.
FIG. 2.

Wheatstone bridge sensitivity when using a NTC thermistor (solid trace) and a PRTD (dashed trace). .

Image of FIG. 3.
FIG. 3.

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 .

Image of FIG. 4.
FIG. 4.

Drive bridge circuit scheme for the square wave bridge supply.

Image of FIG. 5.
FIG. 5.

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.

Image of FIG. 6.
FIG. 6.

IA noise equivalent circuit.

Image of FIG. 7.
FIG. 7.

NET for the IA at different temperatures. The observed discontinuities are caused by the different references, , used at each temperature scale. .

Image of FIG. 8.
FIG. 8.

Sallen-Key Butterworth LPF to avoid aliasing due to high-frequency noise and interference signals.

Image of FIG. 9.
FIG. 9.

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.

Image of FIG. 10.
FIG. 10.

(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 .

Image of FIG. 11.
FIG. 11.

Theoretical FEE global TC, , assuming worst-case conditions.

Image of FIG. 12.
FIG. 12.

(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.

Image of FIG. 13.
FIG. 13.

(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 .

Image of FIG. 14.
FIG. 14.

(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.

Image of FIG. 15.
FIG. 15.

(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. .


Generic image for table
Table I.

Summary of theoretical noise level at and digital parameters involved in the demodulation process.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Thermal diagnostics front-end electronics for LISA Pathfinder