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EET-227 Test #2 Sample Questions True/False Indicate whether the sentence or statement is true or false. ____ 1.

EET-227 Test #2 Sample Questions

True/False

Indicate whether the sentence or statement is true or false.

____ 1. If the gain of a proportional controller is too high, it will cause the controlled variable to oscillate around the set point in the same manner as an on-off system.

____ 2. The magnitude (ignore polarity) of the derivative action is directly proportional to the rate at which the error is changing, whether it is increasing or decreasing.

____ 5. Oscillations are likely to occur in a fast-acting application, such as in a flow control system, if the derivative mode is used.

____ 6. The size of the error signal affects the amplitude of a proportional mode output signal.

____ 7. When the gain of a proportional controller is 4, it will cause the process variable to change more quickly than if the gain is 1.

____ 10. The integral function can be generated if an error signal is reduced to zero.

____ 11. If the duration of an error signal is long enough, the integral output will reduce to zero.

____ 13. The derivative action provides some contribution in eliminating offset.

____ 14. The derivative mode is not recommended in a slow-acting application, such as in a temperature control system.

____ 19. Due to the limited technical credentials of process equipment operators, they should never be consulted before the tuning procedure begins.

____ 22. In a first order-plus deadtime process model, the deadtime refers to the accumulated reaction time delays of the instruments in a control loop.

____ 23. The time constant of the first order process model created by a step change for the direct synthesis tuning method is affected by the size of the process gain.

____ 25. When making a 5% to 10% set point change during the tuning procedure, the product is usually adversely affected.

____ 35. Feedback systems work on the principle that the process must deviate from set point before control action is applied.

____ 36. A feedback control system compensates for an unmeasurable disturbance.

____ 40. The sensing distance of an iron target from an inductive proximity detector is proportional to its thickness.

____ 45. Proximity detectors are capable of producing a linear output signal that is inversely proportional to the distance of the target to the sensor.

____ 46. The demodulator in an inductive proximity detector is nothing more than a filtered half-wave rectifier.

____ 47. A linear inductive proximity detector uses a Schmitt trigger in its internal circuitry.

____ 48. A proximity detector with a 2-inch diameter has a sensing distance that is twice as far as a one-inch sensor.

____ 49. An inductive sensor head flush mounted into a metal plate does not need a shield around its coil because the surrounding material automatically provides the shielding.

____ 50. The recommended diameter of the inductive proximity sensor head is twice the width of the target.

____ 51. The inductive proximity detector senses only a metal target and the capacitor proximity senses only a nonmetallic target.

____ 52. If a film of oil or dirt forms on the head of a sensor, it will not affect the operation of the inductive type, but it may affect the capacitive type.

Multiple Choice

Identify the letter of the choice that best completes the statement or answers the question.

____ 61. The __________ determines the amplitude of a proportional mode output signal.

a.

error signal size

c.

proportional band

b.

gain

d.

all of the above

____ 63. Proportional __________ is defined as the percentage change in the controlled variable that causes the final control element to go through 100% of its range.

a.

gain

b.

band

____ 64. When the gain of a proportional controller is 1, it will cause the controlled variable to change more __________ than if the gain is 4.

a.

slowly

b.

quickly

____ 65. A controller with a proportional band of 100 will move the final control element __________ as much as one with a proportional band of 50.

a.

the same amount

c.

twice

b.

half

____ 72. The derivative mode provides a __________ action when the difference between the set point and measured variable is reducing.

a.

boost

b.

breaking

____ 73. The magnitude of the __________ output is proportional to the time duration that a deviation between set point and the controlled variable exists.

a.

on-off

d.

derivative

b.

proportional

e.

all of the above

c.

integral

____ 76. The derivative output will be the __________ polarity as the proportional output when the error is increasing.

a.

same

b.

opposite

____ 77. By doubling the reset setting on a controller, the time duration of the offset will __________.

a.

double

c.

remain unchanged

b.

reduce by half

____ 78. Which control mode is most influential in reducing overshoot in a system which requires a fast response?

a.

on-off

c.

integral

b.

proportional

d.

derivative

____ 79. The proportional gain will be __________ if a 5 percent input change causes a 30 percent output change.

a.

1.5

c.

3

b.

2

d.

6

____ 80. Proportional __________ is defined as the ratio of change in output to the change in input.

a.

gain

b.

band

____ 81. A(n) __________ of the proportional band causes the magnitude of the controller output to become larger.

a.

increase

b.

decrease

____ 82. If the controlled variable is __________ the proportional band, the proportional action will cause the final control element to be fully off.

a.

below

b.

above

____ 83. As the length of time a steady state error continues, the magnitude of the integral output __________.

a.

increases

c.

does not change

b.

decreases

____ 84. The __________ function of the controller is used to adjust the integral action.

a.

reset

b.

rate

____ 85. The magnitude of the controller output will increase as the reset time programmed into the controller is made __________.

a.

smaller

b.

larger

____ 86. The derivative mode provides a __________ action when the difference between the set point and measured variable is increasing.

a.

boost

b.

braking

____ 87. The derivative output will be the __________ polarity as the proportional output when the error is decreasing.

a.

same

b.

opposite

____ 88. If the error is constant, there is __________ derivative action.

a.

large

c.

no

b.

small

____ 89. Which of the following characteristics describe how the derivative controller affects the response of a controller?

a.

fast initial response

c.

less overshoot

b.

eliminates offset

d.

both a and c

____ 93. The response of the process is identical to the output of a controller in a __________ process model.

a.

pure gain

c.

first order plus deadtime

b.

first order

d.

second order

____ 122. Which of the following functions are performed by limit switches?

a.

detecting the position of an object

b.

detecting the size of an object

c.

counting parts

d.

preventing movement of an object outside a safe zone

e.

all of the above

____ 123. Which of the following circuits are in the demodulator section of a proximity switch?

a.

tank circuit

d.

amplifier

b.

rectifier

e.

both b and c

c.

filter

____ 124. The differential travel property of a proximity sensor is that the target must be __________ to turn on than to turn off.

a.

closer

b.

farther away

____ 125. When the target is within the range of an inductive proximity detector, the sensor's oscillator __________ power.

a.

loses

b.

gains

____ 126. A ferrous target __________ will be detected at the greatest sensing range by an inductive proximity sensor.

a.

with the same cross-sectional area as the sensor head

b.

with twice the cross-sectional area as the sensor head

c.

neither a or b, they are the same

____ 127. A __________ inductive sensor has the longer sensing range.

a.

non-shielded

b.

shielded

____ 128. The sensing distance of a foil target made of a non-ferrous material from an inductive proximity detector is __________ a thicker target made of the same material.

a.

greater than

c.

the same as

b.

less than

____ 129. Inductive sensors with __________ diameters should be used for high speed switching application, such as counting gear teeth.

a.

small

c.

It makes no difference.

b.

larger

____ 133. Which of the following functions are performed by the Schmitt trigger in a proximity detector?

a.

amplification

d.

provides hysteresis

b.

inverts the input signal

e.

both c and d

c.

provides switching action

____ 134. When the target is within the detection range of an inductive proximity detector, its oscillator __________.

a.

stops running

b.

begins to run

____ 135. An inductive proximity detector senses __________.

a.

metallic materials

c.

both a and b

b.

nonmetallic materials

____ 136. A capacitive proximity detector senses __________.

a.

metallic materials

c.

both a and b

b.

nonmetallic materials

____ 137. When the target is within the detection range of a capacitive proximity sensor, its oscillator __________.

a.

stops running

b.

begins to run

____ 138. Referring to the hysteresis property of the proximity detector, the target must be __________ the sensor head to turn it on than to turn it off.

a.

closer to

c.

the same diameter from

b.

farther away from

____ 140. A conductive target changes the value of the capacitor in a capacitor proximity detector by __________.

a.

adding an additional plate

c.

both a and b

b.

changing the dielectric constant

____ 141. Which of the following materials can be detected by a capacitive proximity detector?

a.

liquids

d.

granular materials

b.

nonmetallic solids

e.

all of the above

c.

powders

____ 142. In the above figure, the load is connected across output terminals __________.

a.

T1 and T2

c.

T2 and T3

b.

T1 and T3

____ 143. In the above figure, to operate, the flux lines of the magnetic target must be __________ to the face of the Hall-effect device.

a.

parallel

c.

both a and b

b.

perpendicular

____ 163. If the voltage at the output lead of a three-wire sensor decreases when the sensor is activated, it is a __________ device.

a.

sourcing

b.

sinking

Completion

Complete each sentence or statement.

169. If the gain of a proportional controller is 4, the equivalent proportional band value is ________________ .

170. A reset time of 20 repeats per minute equals an integral time of __________________ minutes per repeat.

171. A time proportioning controller with a DC output voltage of 10 volts will produce an average voltage of ____________________ volts if it is switched on for 70% of the time and off for 30% of the time.

172. The ___________ (smaller, larger) the gain of a controller, the more sensitive it is to input changes.

173. A proportional band of 50 will cause the final control element to change 50 percent if the measured controlled variable changes ____________________ percent.

174. A proportional band setting of 25 percent corresponds to a proportional gain setting of ____________________.

175. An integral time of 0.5 minutes per repeat equals ____________________ repeats per minute.

176. A time proportioning controller with a DC output voltage of 10 volts will produce an average voltage of 5 volts if it is switched on for ____________________ percent of the time and off for ____________________ percent of the time.

182. A shielded sensor uses the ____________________ (radial, axial) approach by detecting objects _________________ ______ (only in front of the head, to the front or side of the head).

183. Referring to the above figure, when a metal target is detected, list the conditions that develop in the circuitry of the inductive proximity detector: The Schmitt trigger produces a ____________________ (low, high) voltage level. The transistor turns ____________________ (off, on). A ____________________ (minimum, maximum) voltage drops across the load.

186. When a conductive target is within the sensing field of a capacitive proximity detector, ___________________ (the object becomes another electrode, the dielectric constant changes) which causes the capacitance to _____ _______________ (increase, decrease).

187. An unshielded sensor uses the ____________________ (radial, axial) approach by detecting objects ___ ________________________ (only in front of the head, to the front or side of the head).

Short Answer

194. List 3 different control modes:

1. ________________

2._________________

3. ________________

195. List 4 elements of a single-variable control loop:

1. ________________

2._________________

3. ________________

4. ________________

196. List 4 factors contribute to the time delay caused by instruments:

1. ________________

2._________________

3. ________________

4. ________________

Problems:

1. A proportional controller has a gain of 25, what is the controller output change, if the input change is 5%?

ANSWER:

2.A capacitive sensor has a rated sensing distance of 30 mm and the target is alcohol. What is the effective sensing distance?

ANSWER:

3. Design a circuit with the following conditions:

1. Use PB1 as Start push button and SW1 is Stop push button.

2. When SW1 is closed, and PB1 is depressed, the Motor M1 is ON and stays ON, even the PB1 is released. The motor M1 is running Forward.

3. When a target is within the sensing distance of Sensor S1 (NORMALLY OPEN, SOURCING), the Motor M1 direction is reversed.

4. Write down all the relay terminals number and wire colours.

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