# RFID Technology as a Low-Cost and Passive Way to Digitize Industrial Analog Indicators
## 5 Discussion  
The metallic covers and parasitic elements cause EM isolation for the RFID tags. Near-field metal covers create an inductive and capacitive coupling that changes the antenna's input impedance. Chip and antenna impedance mismatch causes only a tiny portion of the absorbed energy to be transferred to the chip. If the energy transferred to the chip is less than the \(P_{imin}\), it leads to turning off the chip. \(P_{imin}\) or reading sensitivity means the minimum input power of the chip to turn it on. NXP states that this parameter is \(-17.5\) dBm in SL3s1003, which means that the chip is off as long as the power gain chart is below this value [31]. The intersection of this line (\(-17.5\) dBm) with the gain diagram in Figure 10 shows that the red tag from \(\mathcal{O}=-40^{\circ}\) to \(-140^{\circ}\) and the green tag from \(\mathcal{O}=-219^{\circ}\) to \(-320^{\circ}\) are clear readable for the RFID reader. To better understand the performance of the tags and switching points, Figure 11 shows the trigger angles during a 360-degree rotation of the nanometer pointer. The locating of the nanometer pointer in each zone (red or green) leads to only activating the same zone tag, and the RFID reader easily determines the zone through the EPC code of the chips. In this way, thanks to RFID technology and the EM isolation effect as an advantage, we introduced a method to digitize manometer passively and wirelessly.  
Such an integrated passive RFID tag and the metallic cover allow the manometer to be easily read by already installed RFID readers or by installing an antenna on movable objects (e.g., forklifts, bicycles often used in large industrial plants, or even in the industrial cleaning trolleys), thus reducing the necessary number of readers. The study demonstrated the feasibility of a Passive RFID tag and EM isolation to retrofit industrial analogical devices such as manometers, handwheels, etc., in an effective and low-cost way.  
Figure 10: RFID tag total gain and switching angles.  
**Author Contributions:** Conceptualization, G.F.; methodology, G.F. and S.A.; software, M.H.; validation, G.F. and A.M.; formal analysis, M.H.; investigation, M.H. and S.A.; resources, A.M.; data curation, G.F.; writing--original draft preparation, M.H. and S.A.; writing--review and editing, A.M.; visualization, A.M.; supervision, A.M.; project administration, G.F.; funding acquisition, G.F. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research work was undertaken in the context of DGIGMAN4.0 project (\"DIGItal MANufacturing Technologies for Zero-defect Industry 4.0 Production\", [[http://www.digiman4-0.mek.dtu.dk/](http://www.digiman4-0.mek.dtu.dk/)]([http://www.digiman4-0.mek.dtu.dk/](http://www.digiman4-0.mek.dtu.dk/)), accessed on 21 July 2021). DGIGMAN4.0 is a European Training Network supported by Horizon 2020, the EU Framework Program for Research and Innovation (Project ID: 814225).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors express their gratitude to the anonymous reviewers for their valuable comments that helped us to improve the paper significantly.  
**Conflicts of Interest:** The authors declare no conflict of interest.