TM-9-1200-215-34&P Technical Manual for M109 Automatic Fire Control System (AFCS) Download
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TM 9–1200–215–34&P 2–4 b. During operation, the ACU receives projectile type, propellant charge, relative target location, and miscellaneous information from other AFCS and navigation components, via a 1553B bus. Ballistic processing is accomplished by using equations of motion. Sheaf processing algorithms, compatible with those used by the Battery Computer System (BCS), are used to compute aimpoint offsets. Computed solutions are sent to the ACU weapons controller to implement valid 155mm projectile/fuze/charge combinations. The weapons controller will automatically lay the weapon to the determined azimuth and elevation when the GUN SERVO switch on the Display Unit (DU) is activated. In addition to weapon control function, the ACU interfaces with a gun tube mounted temperature sensor. The ACU interprets temperature data and then monitors the status of the gun tube temperature. The block diagram shown in figure 2–1 illustrates the principal ACU signal flows during operation. c. The ACU consists of a single, sealed, enclosed housing and the following components: D Power Supply Assembly D Central Processing Unit (CPU) Circuit Card Assembly (CCA) D Hard Disk Drive D Servo Controller/Interface Circuit Card Assembly (CCA) D Discrete I/O Circuit Card Assembly (CCA) D 1553 Circuit Card Assembly (CCA) D Tactical Communications Interface Module (TCIM) Circuit Card Assembly (CCA) D Backplane D Solenoid Relay (1) Power Supply Assembly. The ACU power supply assembly converts conditioned vehicle power to properly regulated local system voltage levels required on each ACU shop replaceable unit (SRU). The power supply provides +5.0 Vdc, +15.0 Vdc, and –15.0 Vdc. When 28 volt input power is supplied, the LRU “POWER” LED will illuminate. The power supply also assists in isolating and filtering system power to meet Electromagnetic Interference, Electromagnetic Radiation, and Electromagnetic Pulse (EMI/EMR/EMP) requirements (2) Central Processing Unit (CPU) Circuit Card Assembly (CCA). The CPU CCA is based on a Pentium Processor. It performs all computations of projectile ballistics, relating relevant variables including target position, time on target, gun position, metrological conditions, projectile type, charge type, charge temperature, and tube temperature. The CPU CCA coordinates ACU activities on the local system bus, performs ACU power–up initialization and tests, and performs power–down preparations. Facilities are provided to support the AFCS Built–In Test (BIT) requirements. A diagnostic port allows attachment of an external computer to gain control of the CPU CCA and perform diagnostic tests, including initiating resident tests and downloading new software to be executed on the ACU hardware. There are four Single In–line Memory Module (SIMM) sockets available on the CPU CCA. RAM can be configured from 2MB to 128MB. The default configuration is 32MB of RAM in two SIMM sockets. (3) Hard Disk Drive. The ACU hard disk drive contains 500 to 750 MB of removable internal read/write storage memory. The hard disk drive is user removable without special tools. Operating system and tactical software are resident on the hard disk drive. (4) Servo–Controller/Interface Circuit Card Assembly (CCA). The ACU Servo Interface CCA provides a link between the CPU module and the Servo Controller module. It controls all ACU interaction with the gun hydraulic Servo Controller. The Servo Controller functions to supply operating current to Azimuth and Elevation Electrohydraulic Servo Valves. The Servo Controller is a dual channel, solid state, frequency–compensated, electronic controller . Either channel is capable of energizing the coils of an electrohydraulic servo valve. A dither circuit and linear input circuit for control signal and balancing signals are provided for both sections of the controller. A Servo Continuity Loop is used by the ACU to determine that Azimuth and Elevation Tachometers are connected to the system. These tachometers must provide feedback to the Servo Controller module so that it can properly control the motion of the weapon through the Azimuth and Elevation Servo Valves. Without this feedback, unpredictable movement of the weapon may occur. If the Servo Continuity Loop is closed, the Servo Interface module can activate the Solenoid Relay.