ELEC-304 TQ Review Flashcards
1
Q
The URV of a transmitter is the maximum sensor capability of the device.
a) True
b) False
A
FALSE
2
Q
- What is the accuracy of an analog transmitter, that is turned down 20:1, and has the following accuracy statement?
+/- [0.02(URL/span) - 0.1]% of calibrated span
URL = 750” wc
a) +/- 0.65% of calibrated span
b) +/- 0.3% of calibrated span
c) +/- 0.075% of calibrated span
d) +/- 0.099% of calibrated span
A
b) +/- 0.3% of calibrated span
3
Q
- Why should you not calibrate a transmitter’s 4-20ma output using the test points across the reverse polarity diode?
a) The voltage drop causes a current offset.
b) The current meter is less accurate than measuring voltage.
c) Leakage may exist through the diode which would result in inaccurate calibration.
d) Leakage may occur through the current meter which would result in inaccurate calibration.
A
c) Leakage may exist through the diode which would result in inaccurate calibration.
4
Q
- Why is current used to represent a process variable in a measurement loop?
a) it draws less power from the power supply
b) it has the same value everywhere in the loop
c) it can power the transmitter electronics at the same time
d) it does not require a 250 ohm resistor
A
b) it has the same value everywhere in the loop
5
Q
- Calculate the maximum allowable loop resistance in a two wire transmitter loop with a 20 V power supply and a minimum voltage of 10.5V
a) 160 ohms
b) 475 ohms
c) 675 ohms
d) 1350 ohms
A
C) 475 ohms
6
Q
- What current flows through the rectifying diode in a 2 wire transmitter when an ammeter is connected across the test terminals?
a) The % 4-20ma value
b) 0 ma
c) 4 ma
d) 20 ma
A
b) 0 ma
6
Q
- The best way a ground loop can be eliminated is by:
a) ensuring only one end of the shield is connected to earth ground
b) connecting both ends of the shield to a suitable ground
c) disconnecting both ends of the shield from any ground
d) using UTP wire instead of STP
A
7
Q
- Double grounding a neutral conductor at different physical points could produce:
a) Electromagnetic interference in the conductor
b) A ground loop current path
c) Overheating of the neutral conductor
d) A shock hazard
A
b) A ground loop current path
8
Q
- Instrumentation wiring shields are used to______________________
a) Offset the effect of capacitance interference
b) Eliminate ground loops
c) Establish a common system ground
d) Allow multiple ground points to be established along the wire length
A
a) Offset the effect of capacitance interference
9
Q
- Which common noise source will not be limited using shielding methods?
a) Radiated noise
b) Coupled noise
c) Conducted noise
d) Electromagnetic induction
A
d) Electromagnetic induction
10
Q
- The presence of a ground loop means that extra current may be transferred to the _____________ conductors for that loop.
a) Shield
b) Drain
c) Neutral
d) Signal
A
d) Signal
11
Q
- A common shielding mistake made in industry is:
a) Improper insulating of shields at the ungrounded end of the loop
b) Improper insulating of shields at the grounded end of the loop
c) Not grounding the shields at intervening junction boxes
d) Grounding shields directly to zero potential point of the loop as opposed to a direct earth ground
A
a) Improper insulating of shields at the ungrounded end of the loop
11
Q
- Proper grounding procedures insure that shields and grounds have a continuous, uninterrupted path to_________________ ground.
a) DC ground
b) Chassis ground
c) Earth ground
d) MCC ground
A
c) Earth ground
12
Q
- A twisted wire pair is typically used in many loop applications. The reason twisted wire is used is:
a) reduces electromagnetic induction
b) It eliminates ground loops
c) allows greater baud rate to be realized
d) reduces the capacitance
A
a) reduces electromagnetic induction
13
Q
- What is the % resolution of a 10 bit D/A converter?
a) 0.005%
b) 4.0%
c) 0.098%
d) 0.13%
A
14
Q
- A 12 bit D/A is scaled 0-5 volts. Calculate the output in volts for an input of
708 Hexadecimal (180010).
a) 4.096V
b) 3.49V
c) 5.12V
d) 2.2V
A
d) 2.2V
15
Q
- What type of device is used to convert one form of energy or signal type into another type or form?
a) an H1 to H2 bridge
b) a transducer
c) a IS barrier
d) a microprocessor
A
b) a transducer
16
Q
- A signal converter is commonly used in control feedback systems because:
a) it prevents noise from entering into the control loop
b) it adds intrinsically safe features into the loop
c) it re-ranges the process variables
d) components in a loop do not always recognize the same signal
A
17
Q
- If a HART transmitter is communicating point to point then it is not using
a) Bell 202 protocol
b) FSK signaling
c) Multi drop mode
d) 4-20 mA signal
A
c) Multi drop mode
18
Q
- If a transmitter is producing a NAMUR current output then
a) There is a break in the loop
b) The process variable is out of range
c) The transmitter is connected to the wrong sensor
d) There is a fault in the transmitter itself
A
d) There is a fault in the transmitter itself
19
Q
- One advantage of using a smart transmitter is that
a) Smart transmitters can compensate for ambient temperature variations.
b) Smart transmitters need calibrating more frequently.
c) Conventional transmitters have higher accuracy across the whole range.
d) Smart transmitters can be configured locally while conventional transmitters are configure remotely.
A
a) Smart transmitters can compensate for ambient temperature variations.
20
Q
- Foundation Fieldbus H1 protocol :
a) allows a higher baud rate to communicate bi-directionally with a host and is superimposed on a standard 4-20 mA current signal
b) uses a 2 wire system to provide power to field devices and provide digital communications
c) uses a 4 wire system to provide power to field devices on one pair and provide digital communications on the other pair
d) has the same baud rate as Hart protocol but allows bi-directional communications.
A
b) uses a 2 wire system to provide power to field devices and provide digital communications
20
Q
- What are the characteristics that differentiate a smart from an analog positioner?
a) combines an I/P with the positioner
b) has a feedback linkage to measure stem travel
c) can obtain a valve signature
d) can use 4-20 mA controller output signals
A
c) can obtain a valve signature
21
Q
- What must be done when changing sensor types connected to a smart temperature transmitter?
a) The sensor must be factory matched to the transmitter
b) the sensor type must be entered into the transmitter software
c) nothing- the software will automatically recognize the new sensor
d) the serial number of the new sensor must be entered into the transmitter
A
b) the sensor type must be entered into the transmitter software
22
Q
- When wiring a Digital Output from a SLDC to an inductive load such as a solenoid:
a) The load is energized to be Fail Safe.
b) The load must have an electric current shunt (diode).
c) The load must have a switch to prevent transients (transistor).
d) The leads must be reversed between the output and solenoid.
A
23
Q
- How does a SLDC read a 4-20 mA signal?
a) converts the 4-20 mA to 1-5 volt at the transmitter
b) converts the 4-20 mA signal to 1-5 volts using a 250 ohm resistor at its terminals
c) converts the current using an I/E function block
d) the output of the SLDC is simply connected back to the input terminals, without the aid of a dropping resistor. The conversion is done internally
A
b) converts the 4-20 mA signal to 1-5 volts using a 250 ohm resistor at its terminals
24
Q
- A 10 bit D/A converter is scaled 1-5 V and has an input of 0010 0110 1010. What is output voltage? ( hint: convert binary number to hex then decimal on your calculator) ( use 3 decimal places)
a) 1.41
b) 3.53
c) 2.41
d) 3.41
A
d) 3.41
25
Q
- Error values due to transitions between successive least significant bits
a) quantization error
b) Aliasing error
c) Offset error
d) Sampling error
A
26
Q
- After a zero is performed on a transmitter, the span is adjusted, to match the URV of the sensor, by applying a very accurate sensor span value to the transmitter. This procedure is called a:
a) zero suppression
b) calibration
c) zero elevation
d) re-range
A
b) calibration
27
Q
- What is the process value if the process ranges from 0 to 100 psi and the transmitter sends a 14.5 mA output signal?
a) 59.375 psi
b) 55.4 psi
c) 64.5 psi
d) 65.625 psi
A
d) 65.625 psi
28
Q
- What should be adjusted if process pulsations are causing an erratic transmitter output?
a) zero should be elevated
b) change the loop current from 4-20 mA to 0-20 mA
c) increase damping
d) increase the power supply voltage
A
c) increase damping
29
Q
- The best way to measure the current in an analog loop, set for 4 and then 20 mA, is:
a) measure the total loop resistance
b) measure the loop current with an ammeter
c) measure the power supply resistance
d) measure the power supply voltage
A
b) measure the loop current with an ammeter
30
Q
- The best way to measure the current in an analog loop, set for 4 then 20 mA, without breaking the circuit is:
a) to measure the power supply voltage
b) to measure the transmitter output loop terminal voltage
c) to measure the voltage across a 250 Ω resistor
d) to measure the transmitter supply voltage
A
c) to measure the voltage across a 250 Ω resistor
31
Q
- On an input with an A/D converter, the sampling frequency must be at least 3 times the highest frequency component to accurately reproduce the input signal and prevent which type of error?
a) quantization error
b) Aliasing error
c) Offset error
d) Sampling error
A
b) Aliasing error
32
Q
- If the MSB is the only bit set then the output of a D/A converter that flows through a 250 ohm resistor is ___________ the maximum possible value.
a) Double
b) Half
c) Equal to
d) Quarter
A
b) Half
33
Q
- If digital inputs from more than one source is to be converted to its respective analog signal, and the if the conversion speeds are not excessive then a(n) _______________ could be used.
a) A/D converter
b) Hart Multidrop
c) D/A converter
d) Multiplexor
A
d) Multiplexor
