4th 6th Month Flashcards
An isolated system is not concerned with problems dealing with:
interconnected system operation
Describes a control arrangement where one unit of a multi-unit plant may be assigned to control frequency
Flat frequency control
A control scheme in which each system, interconnected by tie lines is controlling frequency simultaneously is called:
tie-line bias control
A control area
is one or more systems operating with metering and control facilities on all of its ties to other systems outside of the control area.
The combined governor action and inertia of all generating units connected to a system is used to establish:
the frequency bias setting for that control area.
Incremental loading refers mainly to
the economical generation of electrical energy
A procedure whereby two systems, not directly tied together, exchange electrical energy with each other through a third system to which they are mutually connected is called
wheeling energy
An intersystem tie-line meter shows high frequency and power flow out. this would be an indication of:
a loss of customer load or over-generation internally
One essential requirement to be met before two systems consider interconnecting with each other is
that each have the capability of operating independently
Unit control of load and frequency is preferred over plant control because
it provides for quicker response during emergencies
it limits the effects of components failure
units may be loaded more efficiently
Automatic control systems
are frequently used to control a specified sequence of operation
Manual control systems
are frequently used for on=off type of functions
in any system consisting of a combination of manual and automatic controls
means are generally provided for interlocking the various controls
the automatic functions may be bypassed when the switch is turned to manual
protective real operation will take precedence over other types of operations
Supervisory control systems differ mainly from other classes of control systems
in the manner in which commands are transmitted and received
Double transmission is an expression relating to supervisory controls and refers mainly to
security
In a typical supervisory control ooperation
a disagreement lap will light if the wrong button is bushed
The capacity of most supervisory control equipment is determined by
the number of points provided
The reproduction at a convenient location of measurements made at a remote point is called
telemetering
In comparing the merits of analog telemetering with those of digital telemetering it would be correct to say
undetectable errors can be introduced at all points in the former but only at the sending end of the latter
A general digital information handling system would most likely include the ability to
convert solid-state signals to relay actions
convert analog signals to digital information
selectively read information which has been stored in memory
Most PLCs have five common building blocks that originated from what type of relay logic in control circuits
ladder logic
To indentify the location of terminal points, modules, and modular assemblies, a method of addressing or boating these devices is needed in a digital identification system what type of numbers locate devices
binary number
Decimal value 10= what binary number
1010
One of the largest manufacturers of PLC in the US
Allen-Bradley
One of the biggest advantages of a PLC is that a technician can change the ladder logic without reconnecting the
input and output
The processor’s memory section has two areas, they are
program files
data files
Analog input modules are used in PLC systems to perform the conversion from analog signals to digital valures
true
PLC modules that interface with special sensors and devices are available for particular functions
true
Spring-loaded regulators are popular because they are simple, light in weight, and require little maintenance? t/f
True
Why use a nozzle and flapper on a controller
A small force is required to position that flapper and produce a full range of pressure valves for control
name two types of air relays
continuous bleed
hon bleed
To achieve an increase in movement and actuate the flapper in a proportional controller, which method should be considered?
the action of the measuring means
A better solution for mechanical reset for a device is to have it reset manually rather than automatically. t/f
false
list the four modes of controlling
on-off ( two-position)
proportional band
proportional plug rest
proportional plug reset plus rate
how does proportional action work
it positions the valve in proportion to change the controlled variable
Pneumatic controllers for commercial applications usually are of what capability
proportional plus rest plus rate capability
what is used to overcome response lag due to long connecting lines between the controller and valve?
a booster relay installed at the valve location overcomes most of the response lag created by the long connecting lines and insufficient output volume
A basic pneumatic position-er uses what two things
fixed orifice and nozzle
diaphragm pressure
Analog refers to what type of signal
continuous and has an infinite number of points between its beginning and ending valves.
Voltage transmitters are 4-wire transmitters t/f
true
on a proportional controller the desired set point and proportional band are usually adjusted with a potentiometer t/f
true
adding time is the time it takes the controller to adjust itself back to its set point t/f
false
A proportional plus integral controller can be used for the control of flow, gas and liquid pressure or temperature and level applications t/f
true
PID control systems can be used in all systems but perform especially well in systems that have long delays t/f
true
what are PLC’s
programmable logic controllers electronic control devices that perform many logic functions
communications between controllers and computers allow:
data to be gathered
the control of adjustments
the operation of master-slave devices
human machine interface is equipment that allows the operator to interface with the system t/f
true
Data transmission rate is usually expressed in
bauds
Name the three types of bourdon tubes
simple c-tubes
spiral
helical
name the two broad types of diaphragm pressure elements
metallic
nonmetallic
what is used to strengthen a metallic diaphragm unit made from two capsules
a c-spring
on pressure control devices, commonly, the high pressure side is called _____ and the low pressure side _____
upstream
downstream
what is a back pressure regulatot
regulating the rate at which find flows downstream controls upstream pressure. the control of upstream pressure is commonly called back pressure control
slack diaphragm elements are used in draft gauges t/f
true
a manometer is a pressure gauge that responds to large pressure changes t/f
false
a bell-type gauge is
sensitive
accurate
stable
Name 3 types of mechanical pressure elements
four-wire voltage transmitter
two-wire current transmitter
smart transmitter
why is a sight or gauge glass mounted on the side of a liquid tank
it gives visual indication of the level and can be view continuously
How is liquid level measured by the hydrostatic method
for each foot of vertical height a column of water produces a pressure of approx. .433psi. use the formula p=.433gh
g= specific gravity
h= height above the metering ground
A popular method of liquid level measurement uses a differential pressure transmitter to generate a 4-20mA signal? t/f
true
To relieve the load on a pumping system, multiple variable speed motors connected parallel may be used. t/f
true
What is flow measurement
The process of determining the quantity of fluid that passes a particular point in a given interval of time.
Another name for differential pressure is head. t/f
true
The most widely used orifice is
concentric
the equation for velocity of flow
v= square root 2gh
a variable-area flowmeter uses mechanisms that act against the force of fluid flow to drive a pen. t/f
true
list three type of electonic flow meters
magnetic flow meter
mass flow meter
vortex flow meter
a dall tubes design differs significantly from the venturi in two respects name them
an abrubt shoulder at the inlet cone comes after a short uniform section
the low pressure tap at the throat leads to an annular grove that encircles the throat.
A popular mechanical means of measuring differential pressure is based on a mercury-filled u tube manometer t/f
true
The key to a turbine meters operation is a permanent magnet placed in a
coil
a magnetic flow meter restricts liquid to flow t/f
false
a turbine flow meter is simple, easy to install and use, and accurate to within
99%
