Controls Part B Flashcards
What are the three primary reasons for sensing and measuring variables?
To indicate, record and control
What does it mean if a primary sensing element is remote located?
Remote can main panel or board mounted. The sensing device can be located in a process line and the indicator or recorder portion can be located in a control room.
If a primary sensing element is classified as integral, where would the sensing device and indicator be located?
On the process line
What are the four main types of variables to be measured?
Temperature, pressure, liquid level and flow rate.
Is a Bellows actuator filled with a liquid with a high boiling point or a low boiling point?
Low boiling point
What is the purpose of a thermowell?
To protect thermometers and other sensing bulbs from high external pressures, and possible damage.
What is an averaging elements purpose?
To get the reading of the average temperature across the face of a large air heating coil. Differences and temperature at various points are averaged out as a single pressure in the tubing.
The operation of what element depends on the principle that dissimilar metals expand at different rates when heated?
Bimetal element
A helix type bimetal strip would be used in what situation?
To obtain considerable rotation of a pointer on a scale, and spread the scale for maximum accuracy and sensing temperature
What type of element consists of a tube with a high rate of expansion over a rod with a lower rate of expansion?
Rod and tube element
The thermal electric pyrometer method of sensing ____________ is created by using dissimilar metals that when heated will generate a DC current in millivolts.
Temperature
What does a monometer measure?
The difference between two pressures or the differential pressure measurement
Are manometers able to measure vacuum?
Yes
If a longer scale of measurement is required for a more accurate reading what type of monometer is recommended?
Incline tube monometer
What does a compound gauge measure?
A compound gauge can indicate both PSIG (pressure) and inches mercury (vacuum) on the same dial face.
What is used to protect a Bourdon tube from damage due to exposure to steam?
A siphon pigtail or a U trap is used between the gauge and the steam. water should be added to the pigtail to build a water seal
Can a diaphragm element indicate vacuum?
Yes
What is the simplest form of liquid level measurement?
Directly, usually with the aid of a sight glass or other visual level indicator
When using a diaphragm actuated differential pressure transmitter (DP cell) what pressure is on the high-pressure side and the low pressure side of the diaphragm?
The tanks head pressure would be on the high-pressure side of the diaphragm and the low pressure side is vented to atmosphere.
What is required to measure the rate of flow using the differential pressure method in a pipeline?
Some form of restriction placed in the pipeline to create a pressure drop.
When an orifice plate is used to restrict flow in a pipeline , the lowest pressure occurs at the point where the fluid has the smallest cross-sectional area. What is the point called?
Vena contracta
After a fluid passes through an orifice plate and the vena contracta, the pressure begins to increase but never fully recovers due to what?
Permanent loss of energy occurs due to friction and turbulence
An orifice plate with a straight or bevelled edge is installed with the flat face oriented upstream, or downstream?
Upstream
On an orifice plate, which way is the stamped face normally installed?
Normally upstream
What size of pipe are flange taps generally used on?
2 inch and larger
On a full flow or pipe tap where are the connections for the transmitter located?
They’re located on the actual process line, not on the orifice flanges. The upstream high-pressure tap is 2 1/2 pipe diameters from the face of the orifice plate and the downstream, Low pressure pipe tap is located eight pipe diameters from the face of the orifice plate.
Where are the connections for the transmitter for a Vena contracta or radius tap method??
The connections for the transmitter are located on the actual process line, not on the orifice flanges. the high-pressure upstream pipe tap is one pipe diameter upstream of the face of the orifice plate, and the low pressure downstream pipe tap is a half pipe diameter from the face of the orifice plate.
Vena contracta or radius taps are limited to what pipe sizes?
6” and larger
Laminar flow is essential upstream of an orifice plate. The general rules are:
_____ pipe diameters if the disturbance is due to flanges, collars, wide, open gate valves, reducers, elbows, or other changes in direction provided the flow is all in the same plane (horizontal).
_____ pipe diameters are required if a fitting changes the flow in two planes (vertical to horizontal).
_____ diameters required if the disturbance is caused by PRV’s, control valves or similar regulators.
10
50
75
How many pipe diameters are sufficient before a disturbance on the downstream side after an office plate?
5
Straightening veins are how many pipe diameters from the high-pressure tap connection?
Six pipe diameters minimum
How many pipe diameters from the straightening vein to the nearest upstream disturbance?
Four pipe diameters minimum
What element senses impact and static pressure at the same instant?
Pitot tube
Do flow nozzles and Venturi tubes produce less permanent pressure drop or more permanent pressure drop than an orifice plate?
Less
What are the disadvantages of a flow nozzle or Venturi tube versus an orifice plate?
Bulkiness and higher cost
A differential pressure cell can be connected from the high-pressure side upstream tap of an orifice plate and the low pressure side to the downstream tap but what does it measure?
Differential pressure not flow.
Using a DP cell across the high and low pressure sides of an orifice plate requires what to obtain a flow reading?
A mathematical function instrument called a mechanical Square root extractor.
What are three and five block valve manifold used for?
For isolating, purging, venting, and bringing a piece of control equipment online using close tolerance needle valves.
What type of metre consist of a tapered tube in which a float or rotor can move up and down freely the fluid being measured flows through the tube from the bottom to the top, and this causes the float to take position in the tube.
Rotameter or variable area metre
Which type of metre uses the velocity of a moving liquid or gas to react against the propeller type blade, causing the blades to turn, and the rotation of each blade is measured by the electricity it creates?
Turbine flow metre
What type of flow metre offers no flow restriction, but is the most expensive used for flow measurement?
Magnetic flow meter
Primary elements use what range of instrument air and electric signal?
3 to 15 psi or 4 to 20 mV
What range of air pressure does a final control element use?
15 to 25 psi
Heading downstream off of an air compressor tank, would the air filter be first or the pressure reducing valve?
Air filter
What is the industry standard dewpoint?
-40C
For moisture removal purposes, would you size a compressor with a higher operating pressure rating or an adequate operating pressure rating then is required for air supply purposes alone?
Higher
Under what condition would a mechanical air dryer be required?
When compressed air piping is run along outside walls or outdoors.
What does a hygrometer measure?
Moisture content in the instrument air
What type of dryer consists of two identical chambers, valves, a timer and their use is alternated?
Desiccant or chemical dryer
Heatless regeneration of the desiccant means what?
No heat is required to drive moisture from the desiccant being dried
What are the two types of desiccants?
Silica gel beads and activated alumina
An after cooler is a heat exchanger type of equipment, used to cool the air temperature to its dewpoint, for what reason?
To reduce moisture in the air
Where is an intercooler located?
Between the cylinders in an air compressor
The _______ __________is to prevent dust, or other airborne contaminants from entering the intake valves of the compressor.
Intake filter
To maintain the life of the compressor and the warranty the compressor oil used must be recommended by whom?
The manufacturer
Limiting _____________ in compressed air piping as of the upmost importance.
Condensation
Along with the air filter, what other piece of equipment is located in the piping between the compressor and the pressure reducing valve?
The moisture condenser
To decrease moisture in the system, would you be required to increase the air temperature or decrease air temperature?
Decrease
Who are the ISA and what do they write an issue standards for?
International Society of automation writes and issues standards for all pneumatic instrumentation systems.
When troubleshooting the sensing and measuring variables, what element would you be primarily concerned with?
The primary element
When a pressure gauge is located on the process piping is it classified as remote mounted or integral mounted?
 integral mounted
The thermometer is designed to measure:
1. absolute temperature
2. molecular movement
- Molecular movement.
The sensing element normally used in a pressure gauge is what?
Bourdon tube
On what law do floats operate?
Buoyancy laws
Which type of flow measuring device is the only accurate measure of volume?
A. Electromagnetic
B. Positive displacement
C. Orifice plate
B. Positive displacement.
Which type of metre is mainly used used as an indicating device?
A. Turbine flow meter.
B. Rota meter.
C. Magnetic flow meter.
B. Rota meter.
How is moisture introduced into the pneumatic control system?
Through the intake filter
The air compressor is controlled by a:
A. Pressure switch.
B. Float switch.
C. Power switch.
A. Pressure switch.
Is the aftercooler located before or after the receiver?
Before the receiver
What type of air drying technique uses a cooling tower?
A. Chemical dryer
B. Moisture condenser.
B. Moisture condenser.
What is the primary cause of noise transmitted from the compressor?
Vibration
What is the type of piping or tubing found on large pneumatic instrumentation systems?
Galvanized pipe
Before filling and testing a system that contains float type metres what should you do?
A. Check the level.
B. Remove shipping materials.
C. Install plugs.
C. Install plugs.
