# Design and Performance of a XBee 900 MHz Acquisition System Aimed at Industrial Applications
## 5 Validation of the Monitoring System in an Industrial Scenario  
This section focuses on validating the use of the monitoring system in an industrial scenario. For that purpose, an aeronautical reconfigurable tooling prototype, based on a bar-knot structure, which was developed in the context of the SMAR3 NAK research project, funded by the Basque Government (see Figure 13), was chosen. Tests were carried out at the premises of the CTA Foundation, located at the Mifiano Technological Park, in Alava, Spain. This tooling prototype is aimed at adopting different shapes so that different aeronautical parts can be assembled with the same tooling.  
The general objective is evaluating the performance of the proposed wireless monitoring system to monitor strategic sensors located in big machinery in industrial premises, while using wired links for monitoring other sensors. In this case, the operation of positioning an aeronautical reconfigurable tooling prototype was selected. This operation involves monitoring several sensors, located at strategic positions of the tooling prototype, to detect external disturbances that could affect the manufacturing process. Sensors were connected by means of Smart Measuring Nodes. The data acquired by wireless means were compared with the data obtained from the same sensors by using wired links. Experimental tests were carried out at three different distances, namely, 0.30, 6.10 and 12.30 m. All tests lasted around 3 min, since this time is considered adequate for monitoring the bar-knot structure under ramp- and step-provoked disturbances.  
For validation purposes, three different types of sensors attached to the structure were considered. Namely, a strain gauge, a LVDT sensor and a load cell were used to monitor the mechanical strain in a critical bar and the displacement and force values in the knot where the external disturbance is applied. Figure 14 shows the voltage output signals for each sensor. The measurement values obtained with the Smart Measuring Node are shown in blue, while the values obtained by wired links are shown in red. Values were acquired at a distance of 12.30 m from the structure.  
Figure 13: Aeronautical reconfigurable tooling prototype based on bar-knot structure in which the monitoring system was tested.  
Figure 14: Comparison values acquired with sensors located at the bar-knot structure when an external disturbance is applied. Frequency: 10 Hz; Measuring/acquisition separation: 12.30 m. Test duration 3 min. Strain-gauge (top); LVDT (medium) and Load-cell (bottom). Wireless values shown in blue and wired values in red.  
It should be noted that the Smart Measuring Node, powered by an Arduino MKR, only provides a resolution of 12 bits, whereas the NI myRIO provides a resolution of 16 bits. In industrial scenarios, a resolution of 12 bits is frequently considered adequate for a great range of applications.  
Figure 15 compares the values obtained in a different test performed at a frequency of 40 Hz. In this test, only the LVDT sensor was used. Wireless captured values are shown in blue and wired values in red. In this case, the multiple sampling feature was configured. The monitoring system was configured to sample four times every 100 ms, producing an effective sampling time of 25 ms.