Control Instruments Flashcards
Def : feedback control
When an “error” ( difference between desired and actual value) occurs, the control system reacts to reduce the magnitude of the error by changing the manipated variable
Def : feed forward control
Disturbances are measured 1st, calculations if any, then change the manipulated variable
Closed loop difference from open loop
An open loop has no feedback , ie no self correction
Def : measured variable
A quantity , property or condition that is measured also called measurand
Def : setpoint (SP)
An input variable that sets the desired value of the controlled variable
Def : process variable (PV)
Any variable property of a process
Def : error
Algebraic difference between the indication and ideal value of the measured signal
Def : manipulated variable (MV)
The quantity or condition that is varied to correct error ie opening a valve more
Def : controlled variable (CV)
In a contol loop the variable that is sensed so as to originate a feedback signal ie temp of the pipe after the ajax
Def : transmitter
A transducer that senses a measured variable and converts that state to a standardized signal
Def : controller
A device or program that operates automatically to regulate a controlled variable
Def final control element (FCE)
The device that directly controls the manipulated variable. Ie the valve itself
Def : disturbance
An undesirable change in a variable applied to a system which tends to adversely affect the value of the controlled variable
This indicates
Located in the feild
Visible at feild location
Normally operator accessible
This indicates
Located on front of Central consol or main panel
Visible on front of panel / hmi
Normally operator accessible
This indicates
Located in rear of Central consol or main panel
Not visible on front / hmi
Not normally accessible to operator
This indicates
Located on front of secondary or local panels
Visible on front of panel or hmi
Normally operator accessible
This indicates
Located in rear of secondary or local panel
Located in feild cabinet
Not visible on front panel/ hmi
Not normally operator accessible
This indicates
Instrument connection to process and equipment, impulse lines and analyzer sample lines
This indicates
Electrical or electronic signal
This indicates
Pneumatic signal
This indicates
Communication link or bus connecting 2 or more independent microprocessor or computer based systems
This indicates
Filled thermal element capillary tube, filled sensing line between pressure seal and instrument
This indicates
Hydraulic signal
A controller is direct acting if
Its output (CO) increases in response to an increasing measured signal (PV)
This means ? DA or RA ?
Valve fails closed
DA
Controller is reverse or direct
When a controller is in auto mode the operator only controller the
SP - set point
Bumpless transfer is
A smooth transition from auto to manual and back
A direct acting controller calculates error as ___ - ____
PV - SP
A reverse acting controller calculates error as ____ - ____
SP - PV
With an on/off controller
If the error is positive the CO is ___%
If the error is negative the CO is __%
If the error is 0 the CO :
+ = 100%
- = 0 %
0 = CO stays in last position
A transmitter is almost always ____ acting
Direct
____ = e (error) = sp - pv is for
Reverse acting
_____ = e (error) = pv - sp is for
Direct acting
This is? And works?
Forward hysteresis
It changes stat at PV and will not change back till below SP
This is? And works?
Reverse hysteresis. The controller changes state at SP and doesn’t change again till below PV
This is? And works?
Reverse hysteresis. The controller changes state at SP and doesn’t change again till below PV
This is? And works?
Changes state at PV1 and doesn’t change again till below PV2. Both PV are equal from SP
If SP is 40 degrees and PV is 30 degrees calculate pressure
Or (.8 degrees per kpg) +20 kpg
If a tank has a set point of 3 meters ad is using a differential gap of 1.5m what is the UTP and LTP
UTP : 3.75
LTP : 2.25
Explain how this works
When PV is below SP the relay R is closed sending the signal to the FCE. When the PV overcomes the SP it opens the nozzle and therefore the relay cutting off the signal to the FCE
FCE stands for
Final control element
Pid DA : sp __ co __ mv __ RA
DA : up down up
RA : down up down
This is an _____ response
Underdamped
This is an ______ response
Overdamped
This is a _____ response
Critically damped response
This is an _____ response
Marginally stable , aka sustained oscillatons
This is a _____ response
Unstable response
Ramp calc P only
This is
Pulse / response tho pulse
What effect can proportional gain have
Smaller offset , but still takes as long to get to steady state
A FC valve is ___ acting?
Why?
Direct
Increase in signal increases opening
A FO valve is ___ acting?
Why?
RA
Increase in signal decreases opening
PID P is and does?
Proportional
- creates an output signal to the magnitude of the error
PID I is and does?
Integral
- creates a signal proportional to duration and magnitude
- eliminates offset
PID D is does?
Derivative
Output signal proportional to rate of change of error
PID formula?
Co = P + I + D
PID prop calc
P
PID I calc?
I
PID D calc
D
HUH?
