In view of the complexity environment and the urgent need of eld fault diagnosis for Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring(HIRFL-CSR), the detection alarm circuit for equipment fault is designed by using TI's MSP430 mixed signal processor, and using negative feedback to the stability of the circuit, and combining with RS-485 eld bus technology. The hardware system is introduced mainly in this paper, including the constitution and the working principle of the system, the function of the controller, the design of hardware and software. The circuit have the characteristics of fast response, high accuracy, good stability, high reliability, strong adaptability and ascendant quality-to-cost, etc. It can be widely used in the elds of switch quantity diagnosis and alarm system. It has been successfully used in the leakage detection alarm system of HIRFL-CSR.