## 2 Hardware Design and Implementation  
Figure 1 shows the hardware design for the wireless temperature monitoring system. The hardware consists of four layers. From bottom to top, these layers are temperature sensing layer, data acquisition layer, on-site monitoring layer, and the remote access layer. The temperature sensing layer is responsible to measure the raw temperature data from the LPG storage tanks. In this layer, both wireless temperature sensors and fiber optic temperature sensors are utilized. The wireless temperature sensors are easy to deploy while the fiber optic sensor is free of electric shock and can be deployed in certain critical areas. The data acquisition layer is to collect the data from the temperature sensing layer. This layer has routers to receive data from the wireless temperature sensors and demodulators to obtain data from the fiber optic sensors. The demodulator is an OSA with MATLAB programs inside. The programs can calculate the L parameter of the FP cavity and further to get the temperature data by using cavity length _vs._ temperature function we will discuss in Section 2.2. The routers deployed in the fields cover a wide range of area, enabling a large number of wireless temperature sensors to monitor the LPG storage tanks. The on-site monitoring layer, therefore, collects data from routers and demodulators. The on-site monitoring system gets the data from the routers via a wireless receiver and from the demodulator through a LAN cable. With the collected data, the on-site monitoring server displays all the temperature information via monitoring software, which will be further discussed in next section. In addition to data display, the on-site monitoring layer also forwards all the monitored temperature data to the remote server allowing remote access from the clients, which is the top layer of this system. The remote access layer has one server and several clients. The server receives the temperature data obtained from several different on-site monitoring servers, store, and analyze the temperature information in the database. The server  
Figure 1: Hardware design for the monitoring system. As shown in Figure 3, a digital temperature sensor (model DS18B20) and a system-on-chip solution (SoC chip CC2530) were utilized to form the wireless sensing network. The DS18020 digital temperature sensor has a unique one-wire interface which requires only one port pin for communication. It has a temperature measurement range from \(-55\) to \(+125\)\(\;\)C and an accuracy of \(\pm 0.5\;\)C, which make it an excellent choice for the temperature monitoring. The CC2530 chip is an IEEE 802.15.4 compliant true system-on chip, supporting the proprietary 802.15.4 market as well as the ZigBee standards. The CC2530 offers a 101 dB link budget, which has an excellent receiver sensitivity and robustness to interference, four power modes, multiple FLASH sizes, and extensive peripheral set including two USARTs, 12 Bit ADC, and 21 general-purpose GPIO, as well as an industry-standard enhanced 8051 MCU core. The excellent functionalities provided by the DS18B20 and the CC2530 make it possible to achieve a unified design. Schematic design of the Printed Circuit Board for the wireless temperature sensing node, router and receiver are outlined in Figure 6. In the design of the wireless temperature sensing node, an onboard PCB antenna was utilized in order to make the sensing node to be compact in size. In the design of the router and receiver, an external antenna was utilized to achieve high signal to noise ratio. Figure 5: Receiver. Figure 6: _Cont._  
The performances of hardware were tested and Table 1 shows the tested results. The temperature measurement range is 0 \(\,\)C\(\rightarrow\)+125 \(\,\)C which meet the basic temperature monitoring requirements for the LPG storage tanks. The measurement resolution is 0.1 \(\,\)C and the measurement precision is \(\pm\)0.5 \(\,\)C. The data acquisition interval ranges from one second to 24 h and the default set up is 10 min.