Abstract: To address the impact of temperature and humidity on ammunition storage and the shortcomings of traditional ammunition depot temperature and humidity monitoring systems, an intelligent monitoring system was designed using the SHT15 intelligent sensor. The system's structural principle and software design were analyzed. Chinese Library Classification: TP274.5 Document Code: A Article Number: 1006-6977(2006)01-0064-03 1 Introduction Ammunition is primarily stored in warehouses before being used in combat or training. During long-term storage, although ammunition is in a macroscopically static state, its quality continuously changes. This is because ammunition is mainly composed of metal and propellant. During long-term storage, due to the influence of temperature and humidity, the metal will corrode, thereby reducing the strength of metal components and deteriorating surface mechanical properties, seriously affecting the use of ammunition and even causing major accidents. Temperature and humidity also change the physical and chemical properties of the ammunition propellant, causing it to lose its intended combat and technical requirements. Therefore, temperature and humidity are the main contradictions causing changes in ammunition quality. Based on the conditions of our military's warehouses, my country's climate, and current warehouse management levels, the maximum temperature is generally stipulated to not exceed 30℃, and the maximum humidity not exceed 70%, commonly referred to as the "37" limit. Traditional ammunition warehouse monitoring systems use dry-bulb and wet-bulb hygrometers, hair hygrometers, humidity-sensitive resistors, or systems composed of ordinary temperature and humidity sensors. These systems are typically complex, bulky, and inaccurate. This paper uses the SHT15 ultra-miniature, self-calibrating, multi-functional intelligent sensor from Sensirion, Switzerland, to measure parameters such as relative humidity, temperature, and dew point, making it suitable for the design of an intelligent temperature and humidity monitoring system for ammunition warehouses. 2. Performance and Characteristics of the SHT15 The SHT15 sensor is a single-chip, multi-purpose intelligent sensor. It includes not only a miniature relative humidity sensor based on a humidity-sensitive capacitor and a miniature temperature sensor based on a bandgap circuit, but also a 14-bit A/D converter and a 2-wire serial interface. The SHT15 can output calibrated serial data for relative humidity and temperature, eliminating the need for traditional multiplexers, A/D converters, and signal conditioning circuits. This results in a more compact and simpler system structure. The SHT15 can measure relative humidity and temperature at the same location. Its internal structure is shown in Figure 1. The SHT15 has few pins, making it easy to use. Its pin arrangement is shown in Figure 2. Pin functions are shown in Table 1. The SHT15 smart sensor has a relative humidity measurement range of 0–100%, a resolution of 0.03%, and a maximum accuracy of +2%RH. Its temperature measurement range is -40℃ to +123.8℃, with a resolution of 0.1℃. The power supply voltage range is +2.5V to +5.5V, and the response time is less than 3 seconds. System Structure and Principle: This system mainly consists of a microcontroller, a sensor, and an actuator. It uses the AT89C51 low-voltage, high-performance CMOS 8-bit microcontroller. The AT89C51 microcomputer contains 4K bytes of erasable and reprogrammable read-only program memory (PEROM) and 128 bytes of random access memory (RAM), manufactured using ATmel's high-density, non-volatile memory technology. It is compatible with the standard MCS-51 instruction set and also includes a general-purpose 8-bit central processing unit and Flash memory. The powerful AT89C51 microcomputer provides a cost-effective solution. Its main features are as follows: MCS-51 instruction set compatibility; 4K erasable and reprogrammable (>1000 times) Flash ROM; 32 bidirectional I/O ports; programmable UARL channel; two 16-bit programmable timer/counters; fully static operation 0-24MHz; one serial interrupt; 128x8-bit internal RAM; two external interrupt sources; a total of six interrupt sources; direct LED driving capability; three-level encryption; low-power idle and power-down modes; software-configurable sleep and wake-up functions. The AT89C51 and SHT15 communicate via a serial bus. The actuator mainly consists of a motor-controlled cooling unit, heating unit, dehumidifier, and humidifier. The temperature/humidity monitoring system for the ammunition depot is shown in Figure 3. The AT89C51 microcontroller cyclically selects multiple SHT15 microcontrollers in real time to detect temperature and relative humidity values. It then reads and displays the current data values. When the relative humidity exceeds 70%, the microcontroller controls the dehumidifier to start working. If the relative humidity is below 40%, the humidifier starts working. When the temperature exceeds 30℃, the cooling unit starts working; when the temperature is below -12℃, the heating unit starts working. A temperature and humidity report is printed every three cycles. 4. System Programming The system software is written in MCS-51 assembly language and adopts a modular programming approach. It mainly includes modules for initialization, data acquisition, data processing, display, alarm, and printing. The system flowchart is shown in Figure 4. Since the SHT15 contains memory, the initialization program mainly initializes some data in the microcontroller and SHT15's memory, and also initializes the microcontroller's initial state. This system is a multi-channel measurement system. After power-on, the SHT15 enters sleep mode after 10ms. It is only "wake up" and starts working when the microcontroller issues a measurement command. Therefore, the microcontroller cyclically issues temperature and humidity measurement commands to each sensor to achieve multi-channel temperature and humidity measurement. The SHT15 command set is listed in Table 2. Because the data output by the SHT15 has a non-linear relationship with the measured value, non-linear compensation must be performed on the readings to obtain accurate data. For nonlinear compensation of humidity, the following formula is usually used for compensation of 8-bit data: RH=（1.43N-5.127）256（0≤N≤107） (1) RH=（1.11N-28.93）/256（108≤N≤255） (2) For temperature sensors, the following formula is usually used for nonlinear compensation: T=d+d2M (3) N and M in the formula are the output values ​​of the relative humidity sensor and the temperature sensor, respectively, and d1 and d2 are constants, which are determined according to the power supply voltage and the number of bits of temperature data. Each measured data should be compared with the specified value. If it is within the allowable range, the program will proceed to the next step. If it does not meet the requirements, an alarm should be set and the data value at this moment should be displayed. After each cycle, there should be a delay of 1 hour (which can be flexibly selected). This is mainly because there are many wooden structures in the ammunition depot. There is a process for evaporation and absorption of moisture. Measurement is carried out after a certain delay. This can avoid the long-term operation of the sensor and the repeated start and stop of the actuator, save resources, and extend the service life of the system. After every three cycles of measurement (which can be selected as needed), the microcontroller controls the printer to print out the temperature/humidity data from the three measurements for reporting and archiving. 5. Conclusion The ammunition depot temperature and humidity monitoring system designed by the author is based on the SHT15 intelligent sensor. The SHT15 is a new type of sensor based on the intelligent sensor design concept, realizing digital output of temperature and humidity data. It features no need for debugging, calibration, or external circuitry, greatly facilitating its application in the embedded measurement and control field. It represents the future direction of sensor development. The system has a relatively simple structure, small size, and high accuracy, overcoming the shortcomings of traditional ammunition depot temperature/humidity measurement systems.