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 principles and software design were analyzed. 1. Introduction Ammunition is primarily stored in warehouses before it is used in combat or training. During long-term storage, although the 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 the 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 warehouse management level, it is generally stipulated that the maximum temperature should not exceed 30℃ and the maximum humidity should not exceed 70%, commonly referred to as the "37" line. Traditional ammunition depot monitoring systems employ dry 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 utilizes the SHT15 ultra-miniature, self-calibrating, multi-functional intelligent sensor from Sensirion, Switzerland, to measure parameters such as relative humidity, temperature, and dew point. This sensor is suitable for designing an intelligent temperature and humidity monitoring system for ammunition depots. 2. Performance and Features of the SHT15 The SHT15 sensor is a single-chip, 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. It also features a 14-bit A/D converter and a 2-wire serial interface. It can output calibrated serial data for relative humidity and temperature. Therefore, the system eliminates the need for traditional multiplexers, A/D converters, and signal conditioning circuits, resulting 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. [align=center][img=400,235]http://www.e-works.net.cn/images/128123785994687500.GIF[/img] Figure 1 Internal structure diagram of SHT15[/align] The SHT15 has relatively few pins, making it easy to use. Its pin arrangement is shown in Figure 2. The pin functions are shown in Table 1. The relative humidity measurement range of the SHT15 smart sensor is 0～100%. The resolution reaches 0.03%, with a maximum accuracy of +2%RH. The temperature measurement range is -40℃～+123.8℃, with a resolution of 0.1℃. The power supply voltage range is +2.5V～5.5V, and the response time is less than 3s. [align=center]Table 1 Pin Functions of SHT15[img=400,176]http://www.e-works.net.cn/images/128123786220625000.gif[/img][/align][align=center][img=255,182]http://www.e-works.net.cn/images/128123786338281250.GIF[/img] Figure 2 Pin Arrangement of SJT15[/align] 3. System Structure and Principle This system design mainly consists of a microcontroller, sensors, and actuators. It employs 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 timer/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 actuators mainly consist of motor-controlled cooling, heating, dehumidifying, and humidifying units. The temperature/humidity monitoring system for the ammunition depot is shown in Figure 3. [align=center][img=400,158]http://www.e-works.net.cn/images/128123786716093750.GIF[/img] Figure 3 Temperature/Humidity Monitoring System of Ammunition Depot[/align][align=left] The AT89C51 cyclically selects multiple SHT15s in real time to detect temperature and relative humidity values, then reads and displays the 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 machine starts working; when the temperature is below -12℃, the heating machine starts working. Every 3 cycles, a temperature and humidity report is printed once. [b] 4. System Program Design[/b] The system software is written in MCS-51 assembly language and adopts a modular programming method, mainly including initialization module, data acquisition, data processing, display, alarm, printing and other modules. The system flowchart is shown in Figure 4. [align=center][img=343,527]http://www.e-works.net.cn/images/128123786898125000.GIF[/img] Figure 4 System Flowchart[/align] 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 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. [align=center]Table 2 Command set of SHT15[img=400,288]http://www.e-works.net.cn/images/128123787074218750.gif[/img][/align][align=left] Since the data output by SHT15 has a non-linear relationship with the measured value, in order to obtain accurate data, non-linear compensation must be performed on the reading value. For humidity non-linear compensation, the following formula is usually used for 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 sensor, the following formula is usually used for non-linear compensation: T=d+d2M（3） N and M in the formula are the output values ​​of relative humidity sensor and temperature sensor, respectively, and d1 and d2 are constants, which are determined according to power supply voltage and temperature data bit depth. Each measured data point is compared with a specified value. If it is within the allowable range, the program proceeds to the next step. If it does not meet the requirements, an alarm should be triggered and the current data value should be displayed. After each cycle, a one-hour delay (which can be flexibly selected) is required. This is mainly because there are many wooden structures in the ammunition depot, and the evaporation and absorption of moisture takes time. A certain delay before measurement avoids prolonged sensor operation and repeated start-stop of the actuator, saving resources and extending the system's lifespan. After every three cycles of measurement (which can be selected appropriately as needed), the microcontroller controls the printer to print out the temperature/humidity data from the three measurements for reporting and archiving. [b]5. Conclusion[/b] 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 sensors. It features no debugging, no calibration, and no external circuitry, greatly facilitating its application in the embedded measurement and control field. It represents the future direction of sensor development. The system structure is relatively simple. It is small in size and highly accurate, overcoming the shortcomings of traditional temperature/humidity measurement systems for ammunition depots.