Data acquisition: Temperature and humidity measurements
This protocol is extracted from research article:
Practical water production from desert air
Sci Adv, Jun 8, 2018; DOI: 10.1126/sciadv.aat3198

In all the experiments, temperature and humidity readings were acquired using a National Instruments data acquisition system (cDAQ-9174) with a NI 9205 32-Channel analog input and NI 9214 16-Ch Isothermal TC modules, respectively. All data were recorded using LabView 2016. Temperature and humidity measurements were taken at various locations inside the case (at the top and bottom of the condenser, inside and at the surface of the sorbent powder, and at the exterior side wall of the case) and outside of the case (ambient temperature and humidity).

The RH was measured with integrated fast-response (response time, <4 s) circuit sensors (Honeywell HIH-4021) with thermoset polymer capacitive sensing elements. The humidity sensors were calibrated within a range of RH (5% < RH < 90% in 5% RH increments and at T = 25°C) using a HygroCal100 humidity generator (Michell Inc.). The HygroCal100 is equipped with seven built-in HygroSmart HS3 capacitive humidity sensors (±0.8% accuracy) enabling humidity uniformity (less than ±0.5%) across the humidity chamber. An external standard reference precision dew-point meter (Optidew Vision precision, Michell Inc.) with ±0.2°C uncertainty in dew temperature was used to zero the bias error of the HygroCal100. Fifty voltage readings with a sampling frequency of 30 s were recorded at each humidity level, while the hysteresis effects were quantified through a loop of increasing (5 to 90%) and decreasing (95 to 5%) humidity. A linear regression curve (coefficient of determination of >0.99 with 95% confidence bounds) was applied to convert sensor voltage output (0.5 to 3.0 V) to RH (0 to 100%). The total uncertainty of the RH readings was determined to be less than 1%. The detailed uncertainty analysis and the corresponding regression curve are given in section S8.

T-type thermocouples (Neoflon PFA, American Wire Gauge 40, OMEGA Engineering) were calibrated within the range of 15° to 105°C in 5°C increments using a Hart Scientific 9103 dry-well calibrator with an accuracy of ±0.25°C. Forty readings with a sampling rate of 5 s were taken at each reference temperature, and hysteresis effects were determined through an increasing-decreasing temperature loop. A linear regression curve was used for data reduction (coefficient of determination of >0.99 with 95% confidence bounds), giving a bias error of ±0.04°C. The total uncertainty in the temperature readings was found to be less than ±0.25°C. The detailed uncertainty analysis with the regression curve is given in section S8.

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