Unit 7 “Controlling the Process” Flashcards
The basic purpose of process control
to achieve the same desired results time after time
The 3 things that an effective control system must continually do
sensing__________________________________________________________
- _____comparing________________________________________________________
- ______correcting___
set point
desired value of the controlled variable
deviation
difference between the measured variable and the set
point
measured variable
characteristic you observe to determine the actual
status of a controlled variable
disturbance
anything that upsets the process
manipulated variable
what you adjust to keep the controlled variable at its
set point
controlled variable
characteristic to be controlled in the process
transmitter
converts and relays information between sensor and controller
capacitance
the ability to store energy
resistance
opposition to the transfer of energy
final control element
takes action to adjust the manipulated variable
recorder
keeps a continuous record of the value of the controlled variable
sensor
collects information about measured variable_
indicator
device that graphically shows at a glance the value of the controlled variable
feedback control
process control
interlock
are often feedback control loops that safeguard equipment and workers
LIST 2 TIMES WHEN MANUAL CONTROL MAY BE USED IN AN AUTOMATED
PLANT
- __ at start up, until process variable becomes stable enough for automatic controls __
- __ for back up,_in case automatic instruments fail ________
LIST 2 MISTAKES COMMONLY MADE BY A TECHNICIAN WHEN ADJUSTING
A PROCESS:
- ___making more of an adjustment than is required____________________________
- ___making a second adjustment before seeing the results of the first_
proportional control
control element can be in any position within its
__operating range. Example: maintaining liquid level in a tank_
two-positional control -
control element can be in only one of two positions, such as
on/off or open/closed. Examples: heating and air condition units, water heaters, ovens,
refrigerator compressors
automatic control
instruments perform process control tasks. Instrument opens supply valve.
manual control -
human performs some or all of the process control tasks. Operator opens supply valve.
