Control Flashcards
all operations undertaken manually
manual
the majority of operations undertaken manually but some critical parameters controlled automatically
semi-automated
the majority of the plant operations automatically undertaken, with some manual input
fully automated
maintains the process variable as close as possible to the set point
control element
A process plant undergoing ___ processes can be manually operated
slow
level of automated suited for complicated processes
fully automated
for safety reasons a very complicatd process plant involving rapid process changes
level of automatiion suited for a process plant where certain process parameters must be maintained for reasons of safety or product quality
semi-automated
Why plants might not be FULLY automated
- Comparison of the automation capital cost relative to on ite manpower costs
- Available of expertise on site to operate a fully automated process plant
- A dependable power supply
Benefit of process control
- Safer operation
- Consistent specification of produced
- Easier to optimise process
- Data history
- Remote operation from site process plant
- Reduced manpower requirements
in “contact” with the process and gives an output that depends on the variable
sensing elements
takes the signal and converts it to a more suitable form for the processing
signal conditioning
takes the output and converts it is a form suitable for presentation (e.g. analogue to digitial converter)
signal processing
the read out
data presentation element
present a numerical value corresponding to the variable being measured
measurement system
require operator to interpret the measurement and take appropriate action
indicators
able to regulate parameters such as flowrate, vessel fill level electronically
automatic control systems
activities that ensure a process is predictable, stable and consistent operating at the largest level of the performance with only normal variation
control
the variable that you need to control
controlled variable
value that the measurement is desired to be
set point
Adjusted in a prescribed way to affect the controlled variable
Manipulated variable
controls the flows of fluid by adjusting the passage of flow and controls flowrate
control valve
Tag “number” for instruments first letter meaning
defines variable being measured
Tag “number” for instruments second letter meaning
optional modifier to first letter
Tag “number” for instruments third letter meaning
optional indication functionality
Tag “number” for instruments fourth letter meaning
optional definies output functionality
Pressure control techniques
- Direct venting
- Venting of non-condensibles after condenser
- Condenser pressure control by controlling coolant flow
- Condenser pressure by varying heat transfer area via liquid level
