nt analysis) in a controlled environment, to answer to three questions. Specifically, after sterilization of SHT21S sensors with sodium hypochlorite and subsequent reconditioning:(1)Q1: What is the agreement with respect to the reference system?(2)Q2: Can agreement be improved through a simple calibration involving bias compensation?(3)Q3: Which is the smallest difference between measurements of two sensors that should be considered as a real difference?Table 1.Sensor specifications��accuracy.These questions are relevant, since sensors must be sanitized between measurements on different subjects and sensors are, at present, too expensive to be disposable (about 60�).For the experiments a set of four SHT21S sensors which underwent from 10 to 15 sterilization cycles with sodium hypochlorite (S1�CS4) was considered.An industrial oven (Binder FD240, Tuttlingen, Germany) with an insulated chamber was used, to ensure a homogeneous distribution of the temperature around the sensors. Temperature within the chamber can be set with a resolution of 1 ��C. The actual temperature in the chamber is visible through a digital display with the resolution of 1 ��C. The oven thermometer has the specifications reported in Table 1.As further element of comparison for the temperature and as single comparison for humidity, an Amprobe TR300 System (Everett, WA, USA, which embeds temperature and humidity sensors as well as a datalogger) was used (Table 1). The TR300 was set to record a temperature and humidity sample every 2 s.The testing procedure was as follows. After oven warm-up at 30 ��C, the door was briefly opened to position all measurement systems at the center of the chamber, with the sensitive elements next to each other (Figure 1).Figure 1.SHT21S sensors (A) connected to the Seeeduino Datalogger (B) and placed close to the sensing tip of the Amprobe TR300 (C) in the oven.At the time of the TR300 first flash, indicating the start of the programmed recording, the Seeeduino Datalogger was activated and the oven doors were closed. The following temperature ramp was applied in steps of 5 min: 30��, 33��, 36��, 39��, 45��. The actual temperature readings and absolute time were noted from the FD240 display. Humidity could not be controlled, since the FD240 does not have this feature. After completion of the rump, the FD240 doors were opened and the systems stopped. Recordings were then downloaded from TR300 and the Seeeduino Logger to a personal computer.Temperature and humidity recordings from all systems were overlapped for visual inspection (Figure 2a). Spectral analysis was then performed and the cut-off frequency for a Butterworth filter (4th order) was obtained. A low-pass Butterworth filter with cut-off frequency of 0.005 Hz was applied to all signals (Figure 2b).Figure 2.Example of (a) temperature
The astronaut navigation system is one of the most important systems for manned missions on the lunar surface, as it keeps astronauts safe while exploring previously unknown e