Download DPCL Solid State Device Discrete Control Lecture

DPCL
Solid State Device
Discrete Control Lecture
Discrete Input – Output, I/O
All devices/control in this course have been
“analog” measurements; level, flow, temperature
etc.
Discrete control implies two stable “states”,
open-closed, on-off, etc.
Inputs-Outputs
Inputs are push buttons, various switches that
sense physical conditions, such as pressure,
level, temperature, proximity or limit etc.
Outputs are used to control “on-off” devices
such as solenoid valves, motors, relays,
contactors etc.
Terms used to represent discrete behaviour
Binary
0
1
Voltage
0 to 1.5 V3.5 to 5 V(or opposite)
Logic
False
True
Switch
OFF
ON
Level
Low
High
Inputs – Switch Configurations
SPST Single Pole Single Throw:
SPDT Single Pole Double Throw:
DPST Double Pole Single Throw:
DPDT Double Pole Double Throw:
Switches
Process Switches are frequently used as safety
interlocking devices.
Interlock – shutdown system
Pressure, level, temperature, flow vibration etc.
The safe way to wire these devices is to assume that
the normal process condition will result in a closed
switch that is there will be current flow to the device
during “normal” operation. This way wiring
failures will “fail safe”, resulting in the alarmed or
interlocked condition.
Discrete I/O Interfacing
The control equipment, either a programmable
logic controller, PLC or a control system such as
DeltaV Distributed Control System, DCS, requires
its internal circuitry to be interfaced with these
industrial electrical or electromechanical devices.
5V dc TTL (Transistor Transistor Logic) signals
for this interface. Isolate computer wiring with
“field” wiring, via optical or transformer coupling.
Discrete I/O Interfacing
The “field” or machine wiring may be either AC or
DC powered.
Examples of AC and DC interface Input Output
Circuits shown in notes.
Optical I/O Isolation
LAB 4
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For this lab, you will need to design, with DeltaV
function blocks, a sequencing control function.
Experiment 4