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Hall C’s HMS PLC Controls
by Steven Lassiter
What Constituents a PLC System
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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 Layout
Seven Module Chassis
Communication
Module
Remote Chassis
Blank Slots
Communicator
PLC
PSU
Redundancy
Module
Typical I/O Chassis Layout
Ten 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
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Voltage Taps
Current measurements
Strain gauges
Motor drivers (DC &
AC)
• LVDT & position
indicators
• Flow Measurements
• Encoders
Communication
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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
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PLC Rack
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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