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).

Ladder Logic Program

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

PSURemote ChassisCommunicator

PLC

Redundancy Module

CommunicationModule

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

Human to Machine Interface (HMI) RSVIEW & RS-Studio

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.

Hall D’s Solenoid

Hall D

Hall D

Hall D