Top 50 Process Loop Components (PLC) Objective Questions and Answers 1. A basic process control loop will consist of ________ a) Signal converter, resistor, knob, and control valve b) Transducer, valve packing, hex-head wrench, and tubing c) Transmitter, controller, I/P converter, and control valve d) Resistor, capacitor, terminal block, and battery Answer: Transmitter, controller, I/P converter, and control valve 2. In a home heating system, room temperature is ________ A) Setpoint B) Manipulated variable C) Process variable D) Load Variable Answer: Process variable 3. Which is/are the component/s are needed for a 4 mA to 20 mA signal?  A) A power supply B) Wire C) A transmitter D) All of the above Answer: All of the above* 4. Identify the proper sequence of valve actions for a three-valve manifold and bleed when taking a differential pressure transmitter out of service:  A) Close one block valve, open equalizing valve, close other block valve, open bleed B) Open bleed, close one bl

  PID Controller 1. In a proportional temperature controller, if the quantity under the heater increases the offset will: a) Increase b) Reduce c) Remain uneffected d) None of the above Answer: Increase 2. The term reset control refers to: a) Proportional b) Integral c) Derivative d) None of the above Answer: Integral 3. In a PID controller, the overshoots has increased. The derivative time constant has to be __ so as to reduce the overshoots: a) Increased b) Reduced c) Reduced to zero d) None of the above Answer: Increased 4. Proportional band of the controller is expressed as: a) Gain b) Ratio c) Percentage d) Range of control variables Answer: Percentage 5. When derivative action is included in a proportional controller, the proportional band: a) Increases b) Reduces c) Remains unchanged d) None of the above Answer: Remains unchanged 6. Proportional band of a controller is defined as the range of: a) Measured variable to the set variable b) Air output as the measured variable varies

  Actuators 1. A pressure control process using proportional plus integral control has a time constant of 10 seconds. The best choice of actuator would be  a) An electric motor b) A pneumatic diaphragm c) A piston and cylinder d) A solenoid electrical Answer: A pneumatic diaphragm 2. An electronic controller creates a 4 to 20mA dc signal that must actuate a steam valve for temperature control. The best and most economical choice would be to  a) Use an all-electric actuator system b) Convert to a pneumatic signal at the controller and use a pneumatic actuator. c) Use pneumatic actuator with an electric to pneumatic valve positioner d) None of the above Answer: Use pneumatic actuator with an electric to pneumatic valve positioner 3. The basic function of the spring in a control valve is to a) Characterize flow b) Oppose the diaphragm so as to position the valve according to signal pressure c) Close the valve if air failure occurs d) Open the valve if air failure occurs Answer: Oppose the

  Different Types of Valves 1. In which of these treatment systems diaphragm valves are preferred? a) Moving Bed Bioreactor(MBBR) b) Desalination c) Ultrafiltration d) Demineralisation systems Answer: Demineralisation systems 2. Which of these are usually not preferred for frequent operation? a) Ball valve b) Plug valve c) Gate valve d) Butterfly valve Answer: Gate valve 3. Which of the following valves are used in high duty cycle applications? a) Check valve b) Clapper valve c) Ceramic disc valve d) Choke valve Answer: Ceramic disc valve 4. Which valve can be used in the service to handle fluids and gases and at the same time can be used for throttling as well? a) Butterfly valve b) Gate valve c) Plug valve d) Diaphragm valve Answer: Plug valve 5. In globe valves, the flow rate control is determined by _______ a) Size of the opening b) Lift of the valve plug c) Pressure difference d) Gravity Answer: Lift of the valve plug 6. Poppet valves are used in piston engines a) True b) False An

  Process Control Valves 1. What is the velocity of water from a cylindrical valve if the cylindrical valve has a diameter of 10 cm and rate of flow of water in Litres per second is 157L/s? a) 40m/s b) 30m/s c) 20m/s d) 30m/s Answer: 20m/s 2. What is the rate of flow of water in Litres per second from a cylindrical valve if the cylindrical valve has a diameter of 10 cm and velocity of water is 12m/s? a) 100L/s b) 127L/s c) 157L/s d) 94.2L/s Answer: 94.2L/s 3. How many ports does a 3 way valve have? a) 1 b) 2 c) 3 d) 4 Answer: 3 4. How many exit ports does a 2 way valve have? a) 1 b) 2 c) 3 d) 4 Answer: 1 5. What is the final amount of water flowing through a valve in one hour when originally the rate of flow from the valve was 10m 3 /hr which was reduced by 80%? a) 3m 3 /hr b) 4m 3 /hr c) 5m 3 /hr d) 2m 3 /hr Answer: 2m 3 /hr 6. What is the percentage change in amount of water flowing through a valve in one hour when originally the rate of flow from the valve

  Control Valve 1. The definition of split range control valves implies that they are a) calibrated with complementary ranges. b) easily re-ranged for different characteristics. c) equipped with quick-acting positioners. d) only used in sets of three. Answer: calibrated with complementary ranges. 2. The proper “fail safe” status of a valve should always be dictated by a) economic savings b) the nature of the process c) the controller’s tuning d) the controller’s action (direct or reverse) Answer: the nature of the process 3. Calculate the necessary Cv rating for a liquid service valve, given a pressure drop of 24 PSID, a specific gravity of 1.3, and a maximum flow rate of 140 GPM. Assume there will be no flashing or choked flow through the valve. a) 0.1319 b) 32.58 c) 7.583 d) 2585 Answer: 32.58 4. When a valve is installed in a process with where the differential pressure (drop) across the valve decreases with increasing flow, the best trim characteristic to choose for the valve would

  Programmable Logic Controller 1. The acronym PLC stands for a) Pressure Load Control b) Programmable Logic Controller c) Pneumatic Logic Capstan d) PID Loop Controller Answer: Programmable Logic Controller 2. In PLC programming, a retentive function is one that a) Defaults to the “on” state b) Is not reset after a power cycle c) Defaults to the “off” state d) Cannot be edited or deleted Answer: Is not reset after a power cycle 3. A good application for a timed interrupt in a PLC program would be a) A communications function block b) A PID function block c) A math function block d) A motor start/stop rung Answer: A PID function block 4. In a PLC, the scan time refers to the amount of time in which   a) the technician enters the program b) timers and counters are indexed by c) one “rung” of ladder logic takes to complete d) the entire program takes to execute Answer: the entire program takes to execute 5. The difference between online and offline PLC programming is a) whether the PLC i

  live & dead zero 1. What is ‘live zero’? a) Output zero for zero input b) Output non zero for zero input c) Output null for all input d) Output unpredictable Answer: Output non zero for zero input Dead zone is the a) Same as time constant b) Same as transportation lag c) Maximum change in the variable that does not change the reading of the instrument d)  None of these Answer: Maximum change in the variable that does not change the reading of the instrument

Pressure Measurement   1. Another word for “pressure” is a) pH b) Head c) Density d) Force Answer : Head 2. If a force of 3400 pounds is applied to a circular piston 2 inches in diameter, calculate the fluid pressure working against the piston. a) 344.5 PSI b) 270.6 PSI c) 850 PSI d) 1082.3 PSI Answer : 1082.3 PSI 3. Which of the following is not a type of pressure sensing element? a) Bellows b) Bourdon tube c) Manometer d) Orifice plate Answer : Orifice plate 4. If the pressure applied to the “low” side of a ∆P transmitter increases while the pressure applied to the “high” side remains steady, the transmitter output should a) Fail low b) Remain the same c) Increase d) Decrease Answer : Decrease 5. Convert a pressure measurement of 20 PSIA into units of inches water column (gauge) a) 1321” H2O b) 510.1” H2O c) 701.2” H2O d) 146.7” H2O Answer : 146.7” H2O 6. Identify the proper sequence of valve actions for a three-valve manifold and bleed when taking a differen

  Two Wire Transmitters 1. The remote mounting feature of two-wire transmitter near the sensor reduces the effects of _________ a) Noise b) Signal Degradation c) Both a & b d) None of the above Answer: Both a & b 2. Why is an ac power not required in the remote areas or locations for operation purpose of two-wire transmitter? a) transmission power is lowered upto 4-20mA current output signal b) transmission power is lowered upto 1-4 mA current output signal c) transmission power is lowered upto 1-10 mA current output signal d) two-wire transmitters do not operate in remote areas Answer: transmission power is lowered upto 4-20mA current output signal 3. How does the appearance of any noise rather than the electrical noise that intrude in the current output signal of two-wire transmitter get eliminated ? a) by common-mode rejection of transmitting device b) by common-mode rejection of interfacing device c) by common-mode rejection of receiving device d) none of the above Answer:

  Pneumatic Signal , Pneumatic Systems, Pneumatic Control Mechanisms Questions and Answers Pneumatic Signal  1. The standard range for pneumatically transmitted signals is a) 3-15 psig b) 5-20 psig c) 1-10 psig d) 4-20 psig Answer: 3-15 psig  2.  pneumatic signal are the signals produced by changing the air pressure in the signal pipe in proportion to the measured change in a process variable.  a) True b) False Answer: True Pneumatic Systems 1. Hydraulic and pneumatic circuits a) Perform the same way for all functions b) Perform differently for all functions c) Perform the same with some exceptions d) Does not perform all the functions Answer: Perform the same with some exceptions 2. Fluid power circuits use schematic drawings to a) Simplify component function details b) Make it so only trained persons can understand the functions c) Make the drawing look impressive d) Make untrained person to understand Answer: Simplify component function details 3. The most common hydraulic fluid is

  Transmitters Multiple Choice Questions Transmitters 1. AVC stands for ________ a) Abrupt Voltage Control b) Audio Voltage Control c) Automatic Volume Control d) Automatic Voltage Control Answer: Automatic Volume Control 2. In TV transmission, sound signal is ________ modulated. a) Phase b) Pulse c) Frequency d) Amplitude Answer: Frequency 3. Ring Modulator is ________ a) used for DSB-SC generation b) used for SSB-SC generation c) used for VSB generation d) used for AM generation Answer: used for DSB-SC generation 4. What is Carrier swing? a) Frequency deviation b) Width of sideband c) Instantaneous frequency d) Total variation in frequency Answer: Total variation in frequency 5. What is the role of the transmitter in the communication system? a) to decode a signal to be transmitted b) to convert one form of energy into other c) to detect and amplify information signal from the carrier d) to produce radio waves to transmit data Answer: to produce radio waves to transmit data 6. What i

  Process Control System 1. What is a process control system? a) system to keep the parameters at zero value b) system to maintain the parameters constant c) system to keep the parameters at highest value d) system to check the voltage Answer: System to maintain the parameters constant 2. A transducer converts ________ a) mechanical quantity to electrical form b) electrical quantity to physical form c) physical quantity to electrical form d) chemical quantity to physical form Answer: physical quantity to electrical form 3. What is the main objective of process control? a) to control physical parameters b) to control mechanical parameters c) to control optical parameters d) to control electrical parameters Answer: To control physical parameters 4. Physical parameters change due to ______ a) voltage b) current c) internal and external disturbances d) power Answer: internal and external disturbances 5. A process control system consists of _____ a) 10 elements b) 6 elements c) 2 elements d

  Elements of process control loop 1. Identify which of the following is an example of a “primary sensing element”: A) I/P transducer B) Instrument signal cable C) Control valve D) Diaphragm E) Digital controller Answer : Diaphragm 2. In order for a control loop to work well under a wide range of conditions, it must possess: A) Calibration drift B) Hysteresis C) A very expensive transmitter D) Proper documentation E) Negative feedback Answer : Negative feedback 3. Which of the following is not a “final control element”? A) A pressure transmitter B) An electric motor C) A heating element D) A control valve E) A servo Answer : A pressure transmitter 4. The purpose of a “shield” wire on an instrument signal cable is to: A) Hold a steadier setpoint value B) Ensure technician safety C) Minimize the possibility of sparking D) Protect the cable from corrosion E) Minimize electrical noise Answer : Minimize electrical noise 5. The most common analog signal standard for industrial process instru