Transcript Electric control

Electric control
Presented by
Andrew
Mitch
Sav
Little Phil
Justin
Safety requirements
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Correct electrical testing
Correct electrical isolation procedures as a
lot of the control gear is 240 V
Care needs to be taken if the system is 24
v as circuits are easy to damage and costly
to repair
Avoid contact with elements with in the
system as they may have harmful contents
being controlled
Principles
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Uses signals sent or switch between electromechanical devices to
control valves dampers pumps just to name a few
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There are many applications where electric control can be used
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Can easily be integrated in to pneumatic or electronic control
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Is made up of three main components
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First the disturbance sensing device
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Second the controller
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Thirdly the final control element
Disturbance sensing device
(sensor)
 Device
that is with in the occupied space
which senses various elements of the
space providing information to a controller
 Is the eyes of the system
 There are many different types of DSDs
dependant on the application desired
Disturbance sensing devices
 Float
switch
 The float mechanism works by either by
making or a contact or by driving a valve
arm to open or close a valve needle and
seat
 The most common form of float
mechanism is in your toilet systern
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Flexible diaphragm
Is a flexible material mounted within a housing
that as the pressure changes the material flex’s
driving an attached arm either backwards or
forwards
Pressure Bell
Sensitive to small changes in pressure
Consists of a bell shaped cap floating on oil that
coves a stem with a hollow in the middle that
allows pressure to build up under the bell
causing it to move
 Often used in pairs in a scale shape
arrangement
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Bimetal element
Two dissimilar metals are bonded together and
because of their two different coefficients of
expansion they bend or straiten on change of
temperature most common use of bimetal strips
is in thermostats
 Rod and tube type element
A high expansion metal tube with a low
expansion metal rod inside and bonded at one
end when the temperature around tube changes
the high expansion metal changes length
Often used in insertion and immersion temp
controls
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bellows
There are three types of bellows
Fluid inside fluid outside and sealed
 Fluid inside bellows
The fluid inside bellows have a linkage fixed on
one end and the other end is connected to a
fluid source as the fluid source changes
pressure the bellows move
 Fluid outside bellows
The fluid outside are mounted within a housing
which gets filled with fluid and as the pressure
changes in the fluid it pushes on the bellows
causing them to move the linkage is connected
to the inside of the bellows
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Sealed bellows
Theses are liquid or gas filled bellows much like
the liquid inside bellows except that the sensing
substance is sealed in and uses a remote bulb
to activate the bellows
 Remote bulb
Is a bulb connected to sealed bellows or a
diaphragm by a capillary tube which when the
bulb chances temp it changes the pressure of
the liquid or vapour within the bulb and capillary
causing drive device to move
 Fast
response bulb
A fast response bulb is a capillary tube
wound in the shape of a bulb due to the
greater surface area of the coils the bulb I
able to respond up to 7 times faster than a
normal remote bulb
 Averaging element
It is a cross between a remote bulb and
fast response bulb it has the capillary the
same as a fast response only the bore is
larger giving it the same volume as a
normal remote bulb
 The
averaging element is distributed
across the cross section of the duct evenly
for a more reliable average of duct
temperature
 Nylon ribbon / human hair
Nylon and human hair absorb moisture
from the air around
Human hair or nylon is stretched between
two points on a pivot which as the hair or
nylon absorbs moisture from the air gets
longer it effects the position of the pivot
arm
 Wooden
element
 One end of a piece of timber is anchored
so it can move and the other is free to
move the free end is connected to a
linkage that as the timber absorbs
moisture the linkage is move as the timber
expands this type of sensor is very slow
acting
 Seldom used these days
 Mercury
switches
 Mercury switches are a glass tube filled
with mercury fitted to a rotary plate driven
by linkages the class tube also has contact
pins fitted and the tube rotates on the plate
the mercury moves making or breaking the
contact pins
Controller
The controller receives information from
the disturbance sensing device then
decides what to do with the information
once it makes a decision it then switches
the final controller to do a give task
 The controller is the brains of the system
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Forms of control
 On off control
 On off control is as the name suggests the
controller simply turns the point on or off
as demand requires
 Multi position on off control
 Is where there is more than one on or off
call per mode of control I.e. one for heat 3
for cool allowing to run more than one
stage of cooling
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Floating control
Similar to on off control except that the controller
has two sets of contacts within it as temperature
changes it can rotate to heat or cool dependant
on what is required at the time this then can
drive final control device open or closed
dependant on what is required
Proportional control
Proportional control is similar to floating control
except for instead of using a mercury switch it
uses a potentiometer to control movement of the
valve dependent on which side the current is
flowing the greatest
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Snap acting switches
Has a snap acting arm that snaps from one
contact to another contact when driven by a
plunger
Mercury plunger relays
Work similar to a solenoid valve it has a glass
tube filled with mercury a insulated contact runs
up the center and one in the base of the glass
tube at the top of the center contact there is a
ceramic cup also filled with mercury around this
contact there is a ferrous tube. this is all
surrounded by a electric coil that when
energized drive the plunger down making
contact between the two contacts causing a
circuit to form
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Electromagnetic switches
Are simple relays where one voltage is used to
operate a coil opening or closing contacts which
may be carrying a greater current or load
Potentiometers
Potentiometers are fine wire wrapped around a
core with a wiper contact that slides along the
wire wrapped around the core dependant on the
position of the wiper the resistance changes
within the core wire thus controlling the amount
of current that flows through
These are used to control modulating valves
Final control
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Final control refers to the final element that is
actually connected to the valve linkage or
damper linkage to actually drive the given item
It is the part of the system that does the work
it’s the hands of the system
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Actuators and linkages
There are two main forms of final control
devices valves and dampers valves to control the
flow of liquid and dampers to control the flow
of air these are driven by actuators connected to
drive motors
An actuator is the piece of equipment that
starts, stops and varies the operation of the final
control element the linkage is the flexible jointed
parts that connect the actuator to the final
control element
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Valves
Valves control the flow of liquid or vapour by
opening or closing a plunger the plunger is
connected to a stem which is driven by an
actuator
Valves come in different types 2 way or 3 way
valves 2 way are a open close type
three way change the flow direction allowing
parts of the system to be bypassed for example
hot or cold water coils in AHUs
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Dampers
Damper are blade shaped louvers that as they
rotate can control the amount of air that flows
across them they proportion the amount of air
that flows across them by opening or closing to
particular degrees of rotation the dampers are
driven by actuators and motors
Communication between
elements
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The three elements communicate with
each other via electrical wiring this
allows the communication to occur
instantly and the distance between
parts can of great distances
Commissioning
requirements
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Check al connections are tight and secure
Check all connections are correct polarity
Check all components correctly installed and
in the right place
Check correct labeling
Check wiring for signs of damage
manually give components signals to ensure
all components working to design
Turn system to auto to ensure all
components work together as per design
Check for leaks on all valves and dampers
Service requirements
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Check al connections are tight and secure
Check all installations are still correctly installed
Check correct labeling
Check wiring for signs of damage
manually give components signals to ensure all
components working to design
Turn system to auto to ensure all components work
together as per design
Check for leaks on all valves and dampers
Lubricate all moving part that require lube
THAT’S ALL
Further information can be
found in the honeywell
manual from the MRB