1. Introduction Ammunition is primarily stored in warehouses before it leaves the factory and is 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, thus 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 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 warehouse conditions of our army, China's climate conditions, and the current level of warehouse management, it is generally stipulated that the maximum temperature should not exceed 30℃ and the maximum humidity should not exceed 70%, commonly known as the "37" line. Traditional ammunition warehouse monitoring systems use dry-bulb and wet-bulb hygrometers, hair hygrometers, humidity-sensitive resistors, or monitoring systems composed of ordinary temperature and humidity sensors. These systems are usually complex in structure, large in size, and have poor accuracy. 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. It is suitable for the design of an intelligent temperature and humidity monitoring system for ammunition depots. 2. Performance and Features of the SHT15: The SHT15 sensor is a monolithic, multi-purpose intelligent sensor. It includes a miniature relative humidity sensor based on a humidity-sensitive capacitor and a miniature temperature sensor based on a bandgap circuit, as well as a 14-bit A/D converter and a 2-wire serial interface. It can output calibrated serial data of relative humidity and temperature, so the system no longer uses the multiplexer, A/D converter, and signal conditioning circuit required in traditional designs. The system structure is relatively compact and simple. The SHT15 can measure relative humidity and temperature at the same location. Its internal structure is shown in Figure 1. The SHT15 has relatively few pins, making it easy to use. Its pin arrangement is shown in Figure 2. Pin functions are shown in Table 1. The relative humidity measurement range of the SHT15 intelligent sensor is 0–100%. The system boasts a resolution of 0.03%, a maximum accuracy of +2%RH, a temperature measurement range of -40℃ to +123.8℃ with a resolution of 0.1℃, a power supply voltage range of +2.5V to 5.5V, and a response time of less than 3 seconds. 3. System Structure and Principle This system design mainly consists of a microcontroller, sensors, and actuators. It utilizes the AT89C51 low-voltage, high-performance CMOS 8-bit microcontroller, containing 4Kbytes of erasable programmable read-only 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 functional characteristics are as follows: • Compatible with MCS-51 instruction set; • 4K FlashROM (erasable and rewritable more than 1000 times); • 32 bidirectional I/O ports; • Programmable UARL channel; • Two 16-bit programmable timers/counters; • Fully static operation 0-24MHz; • One serial interrupt; • 128x8bit internal RAM; • Two external interrupt sources; • A total of 6 interrupt sources; • Can directly drive LEDs; • 3-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 of the ammunition depot is shown in Figure 3. The AT89C51 cyclically selects multiple SHT15s in real time, causing them to detect temperature and relative humidity values, 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 Program Design The system software is written in MCS-51 assembly language, employing 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 begins operation when the microcontroller issues a measurement command. Therefore, the microcontroller cyclically sends temperature and humidity measurement commands to each sensor, achieving 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≤Ⅳ≤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 long-term operation of the sensor and repeated start-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/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 embedded measurement and control. 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.