220 likes | 247 Views
Hall C’s HMS PLC Controls. by Steven Lassiter. What Constituents a PLC System. PLC (processors) Programming. I/O modules. Field Device Signals (sometimes signal conditioners are needed). Communication/Interfacing to other systems. Wiring and associated hardware (Racks, local controls).
E N D
Hall C’s HMS PLC Controls by Steven Lassiter
What Constituents a PLC System • PLC (processors) • Programming. • I/O modules. • Field Device Signals (sometimes signal conditioners are needed). • Communication/Interfacing to other systems. • Wiring and associated hardware (Racks, local controls). • Human to Machine Interfaces, HMI. • Databases and security.
What is a PLC? • Programmable Logic controller : miniature industrial grade computers consisting of hardware and software used to perform control functions. • The first PLC was developed in Bedford Ma. in 1968 and was called a Modular Digital Controller (MODICON) and was used by GM to replace mechanical relays. • The CPU reads input data from field devices via input modules, executes a control program and writes output.
PLC Programming • Programming can be done by a combination of computer languages: ladder logic, function blocks, flow diagrams, Basic and even C to name a few. • Programming is sequential for the most part. • Certain tasks(programs) can be given higher priority (scan rate).
Function Block Program One PID Function block can have over 160 parameters in it.
Program compiler Many Subprograms (Tasks)
Inputs /Outputs • Inputs can be analog (voltage or current) or discrete voltage signals (1 or 0). • PLC uses input/output modules to handle signals from field devices. • Can also use higher level communication devices: RS232, Ethernet, etc. • Many third party devices can talk to the PLC.
PLC Redundant Chassis LayoutSeven Module Chassis Communication Module PLC PSU Redundancy Module Remote Chassis Communicator Blank Slots
Typical I/O Chassis LayoutTen Module Chassis PSU Communication Module to PLC
Field Devices • Temperature Sensors • Magnetic field measurements • Pressure gauges • Vacuum gauges • Cryogenic Liquid Level Meters • RS232/ RS434, etc • Relays • Voltage Taps • Current measurements • Strain gauges • Motor drivers (DC & AC) • LVDT & position indicators • Flow Measurements • Encoders
Communication • Information can be passed to the PLC through: • Backplane • Controlnet • Devicenet • Ethernet • Uses OPC (OLE for Process Control) • OLE = Object Linking & Embedding.
ControlNet is one way that the PLC talks to remote I/O. RG6 cable terminated on each end. Remote I/O can be located up to several Kms away.
Cabling and Racks • PLC Rack • Local Control Rack / Signal Conditioning
Conclusion • Truly Redundant systems: Dual PLCs, I/Os, communication devices. • Hot Swap of I/O devices and PLC (when redundant PLCs are in use). • Ease of programming, auto tag name generator and predefined logic code, drag and drop programming. • Reliability is very good, especially in harsh environments, although intense radiation is always a problem. • Service and monitoring by engineers from home base, reduces downtime (wait-time). Web Based HMIs. • Security of critical sensitive areas. Users may only have restricted, well defined access to magnets. • Trending, maintaining of databases and keyboard entry logging are readily available. • Capability to read/write to EPIC variables exists.