ac study Flashcards
Hydraulic actuators generally operate at lower pressures than pneumatic actuators
False
In thermocouple circuits, cold junction compensation is used to eliminate errors due to the effects of
ambient temperatures
The coefficient of __________ expansion is the amount a unit volume of a material expands or contracts with temperature changes
volumetric
____________ are commonly used in industry to identify equipment that is running hotter than normal
Thermal imagers
RTD’s, thermistors and strain gauges are essentially resistors T/F
True
Feedback Control is commonly implemented using digital computers. T/F
true
Which of following input transducers would function by a change in resistance ?
- Thermistor
- RTD
- Strain Gauge
all of them
In a closed loop automated system the error signal is determined from the sensor feedback signal and the _________ signal.
Set point
What is an actuator?
A device that adjusts the process variable
Modern _________ contain instruments that can use inputs from many types of devices and combine digital and analog output signals to a controller.
control loops
The letter designation for thermocouple wires specifies a _______________.
voltage-temperature relationship
In batch production applications, ____ are the two most common process variables that must be regulated to control the rate of reaction.
temperature and pressure
A transmitter __________.
a)
converts a signal from the sensor into a standardized signal
b)
is used to boost and send signals to a remote location
Both a and b
A new steady-state condition occurs ____ time constant(s) after a controlled variable is exposed to an energy change.
5
I operate by sending sound waves toward the target & measuring the time it takes for the pulses to bounce back.
Ultrasonic Sensor
If a pressure gauge displays a reading of 50 psig, what is the absolute pressure?
about 65 psia
Which of the following devices is used for sensing the position of an object by measuring the time it takes for a transmitted pulse to be echoed back?
Ultrasonic Transducer
Some open-loop automatic control systems are self-regulating. T/F
False
A sensor is usually a transducer. T/F
True
The hydrostatic pressure created by a liquid in an open container __________ when its temperature increases.
stays the same
What is the primary function of an “actuator”?
Alter the process variable
What name is usually given to the system element that is described in the diagram below as a “Summer ”?
Comparator
The psia pressure reading of an inflated tire is the pressure __________.
above a vacuum
Feedback Control is always implemented using digital computers. T/F
False
In a time of flight ultrasonic flow meter, the difference between the transmitted and received frequencies become __________ as the velocity of the fluid increases.
greater
Which of the following types of energy are radiated from a perfect blackbody?
a)
emitted
b)
reflected
c)
transmitted
d)
all of the above
a)
emitted
Assume two ingredients are added together, processed & then stored.
This would be an example of a (n):
a)
Discrete product - producing process
b)
Batch process
c)
Continuous process
d)
Individual product-producing process
b)
Batch process
When testing an RTD, it is not necessary to disconnect it from the circuit
False
The automatic control of process operations are performed by ____.
a)
open-loop systems
b)
closed-loop systems
c)
both a and b
C both a and b
Signal conditioning involves:
c)
converting input & output signals to a usable form
Which of the following terms identify the unit of measurement for flow?
a)
volumetric flow rate
A new steady-state condition occurs ____ time constant(s) after a controlled variable is exposed to an energy change.
b)
5
Illustrated here is a solenoid valve.
They are available to control:
a)
oil flow
b)
air flow
c)
water flow
d)
all of the above
D all of the above
The altitude at or above sea level must be considered when measuring hydrostatic pressure of a liquid in an open container.
True
A component of a device or system
Element
A decrease in signal magnitude.
Attenuation
The ratio of the change in output for a given change in input.
Gain
The upper limit and lower limit in a quantity to be measured.
Range
A device which responds to a measured variable and converts it to a standardized signal.
Transmitter
The difference between the upper and lower values in a measured quantity.
Span
The device which directly responds to the measured variable.
Sensor
Data represented by a set of separate and distinct numbers.
Discrete signal
Data represented by a set of binary numbers.
Digital signal
The smallest interval between sequential values.
Resolution
What is a tuning parameter?
A parameter that determines the accuracy of a controller
A(n) ________ is an electrical meter consisting of several thermocouples connected in series to provide a higher voltage output
thermopile
A boiler operator is typically responsible for control systems that measure temperature, pressure, flow, and other variables.
True
A thermocouple produces a voltage that is proportional to the __________.
difference in temperature between the hot and cold junction
The ____ is sent to the final control element.
control signal
A “Variable Gain Error” in a measuring device is also known as a _____________ error.
Linearity
Hydrostatic pressure is determined by the __________ of the material in the vessel
a)
density
b)
height
c)
both A and B
d)
None of the above
c)
both A and B
__________ readings of a thermocouple are taken to determine temperature measurements
b)
Voltage
What is a deadband?
A range of values in which the process variable can fluctuate without triggering an adjustment
How an indicated value conforms to an accepted standard value
or true value. Normally “reference accuracy” is used which defines
the limit that errors will not exceed when the device is used under
reference operating conditions. Reference accuracy is normally
expressed in a number of forms typically preceded by a+ and a -
sign. e.g. ±0.1 °C, ± 2% of scale length. (Do not confuse with
precision)
ACCURACY
signal representing a variable which may be
continuously observed and continuously represented.
i.e. The signal has an infinite number of points between
any two values.
ANALOGUE SIGNAL
A transducer converts:
One form of energy to another
decrease in signal magnitude. Also, the reciprocal of gain.
ATTENUATION.
When a valve is selected that is sized too large, the controller of the closed-loop system will cause it to operate at or near the ____ position.
closed
When the core of an LVDT is located above the center position, the AC waveform at the secondary is ___________ phase shift with the primary
0°
A domestic “Automatic” washing machine is an example of a closed loop control system
False
Which of the following input field devices would most likely be used with an analogue interface input module?
Photocell
What is a process variable?
A variable that changes during a process
The voltage _______________ at the secondary indicates if the core of an LVDT is located above or below the center position
phase
Simple “ON-OFF type” control is used in which of the following heating systems?
a)
Electric baseboard heaters controlled by a line-voltage thermostat
b)
A domestic central natural gas forced air furnace controlled by a low voltage mercury switch type thermostat
Correct Answer
c)
Both above choices are correct
d)
None of the above are correct
C) both a and b are correct
The emissivity value of a non-blackbody is ______________.
Less than 1
- Determine the angular distance the encoder shaft moves for the four pulses.
( 4 pulses / # of pulses per revolution) x 360 degrees
- Because of the difference in the pulley diameters, the angle traced out by four pulses in the larger pulley will be less than the angle in step 1 above.
Encoder shaft angle in Step 1 x (# encoder teeth / # drum teeth) = angle on shaft drum.
- Find drum circumference = π x 14 cm = 43.96 cm for one revolution.
4.Final answer: (angle on shaft drum in Step 2 / 360 degrees) x 43.96 cm =
This drawing shows the rear drum of a conveyor belt.
This drum is 14 cm. in diameter.
The timing gear on this drum shaft has 28 teeth.
The timing gear on the encoder shaft has 18 teeth.
This encoder is rated to put out 350 pulses per revolution.
How far will the object travel on the belt during 4 pulses of encoder output?
From the list below, select the example of an output transducer
a)
Infrared LED
b)
Strain Gauge
Incorrect Response
c)
Thermistor
d)
RTD
a)
Infrared LED
______________ pressure can have a negative measurement reading
gauge
A __________ is capable of accurately measuring temperatures from a distance.
pyrometer
Which of the following Transducers are considered to be “active” Transducers?
1)
Limit Switch
Incorrect Response
2)
Inductive Proximity Switch
3)
Capacitive Proximity Switch
Correct Answer
4)
Piezo Crystal
5)
All of the above
4)
Piezo Crystal
A load demand change will alter the value of a controlled variable.
False
The _____________ of the secondary voltage of an LVDT indicates how far the core has moved.
amplitude
a calibrated input range of -80 to 100 degrees F,
with an output range of 4 to 20 mA.
Using the calibration table below, what is the applied input temperature for this transmitter? (Assume perfect calibration)
Applied Input Temperature (°F) % of Span Output Signal (mA)
? ?? 50%
_____________________°F
(Place just your number in the space provided, using one decimal place)
Answer:
10.0
Hide question 6 feedback
Feedback
Find the input span total, from the negative low to positive high.
Apply the % given to this total span.
Subtract the negative amount to find temperature
answer
A conductive probe makes __________ measurements.
point
An ____ diaphragm valve allows flow to pass when the activating signal is not applied.
air-to-close
What is the purpose of process control?
To maintain a consistent quality of a product or process
The most common combination of control modes found in the typical process plant is:
Proportional-plus-integral
The four main measurements in process control are :
pressure, flow, temperature, & level.
As the fluid flow through an orifice plate reduces by 3 times, the differential pressure across it ______ times
reduces by 9
What is an active transducer
Active transducers generate energy output by changing the input! No external power source is required.
With a capacitive probe, the level of a solution in a tank determines the capacitance by effecting the __________.
dielectric
A solenoid actuator has a(n) __________ in its symbol.
S
What is a derivative controller?
A controller that adjusts the process based on the time rate of change of the error
What is feedforward control?
A control system that anticipates changes in the process and adjusts accordingly.
An instrument index lists the manufacturer of the devices in a process. T/F
Trrue
Which type of encoder is normally used if angular position is required ?
Absolute
What is a control valve
A valve that controls the flow of fluids or gases in a process
Which type of control is used to adjust the speed of a motor?
Servo control
A controller with what kind of control mode eliminates offset automatically? ________
Integral
The function of the optical encoder’s Schmitt trigger is to convert ______________.
pulses into square waves
The power source of static pressure is __________.
gravity
Variable resisitance sensors that have a positive temperature coefficient include:
R.T.D.’s
The term __________ is used to describe how consistently a sensor responds to the same input value
Reliability
infrared radiation is that part of the electromagnetic spectrum with ______________ wavelengths than visible light
longer
What type of control system is used to control the temperature of a furnace?
Proportional control
The hydrostatic pressure created by a liquid in a closed container __________ when its temperature increases.
increases
The differential pressure method takes measurements in a(n) __________ container.
pressurized
You can use a capacitance sensor to measure
position
What is the difference between a set point and a process variable?
The set point is the target value, while the process variable is the measured value.
Which electrical component does not have analog characteristics?
Temperature Switch
What is a proportional-integral-derivative (PID) controller?
A controller that adjusts the process based on a combination of proportional, integral, and derivative control actions
What type of capacitance sensor can detect the presence of an object without actually touching it?
Proximity detector
Which of the following factors contribute to the dynamic response of a single control loop?
a)
the instrument in a control loop
b)
the inertia of the controlled variable
Incorrect Response
c)
dead time
Correct Answer
d)
all of the above
all of the above
An RTD increases its resistance when it is exposed to _________________.
heat
What type of control system uses a combination of feedback and feedforward control?
Hybrid control
Which electrical component does not have discrete characteristics.
Thermistor
Which transducer is a packaged silicon P/N junction that can detect IR light when reverse biased?
photodiode
____ control valves are not used for high pressure application.
Single-seated
Which component of a control system generates the output signal?
Controller
__________________ is the degree to which an observed value matches the actual value of a measurement over a specified range
Accuracy
What is a proportional-integral-derivative (PID) controller?
A controller that adjusts the process based on a combination of proportional, integral, and derivative control actions
