manual for models: scb37-180 scb107-180 scb107e … scb37-180.pdf · manual for models: scb37-180...
TRANSCRIPT
MANUAL FOR MODELS:
SCB37-180
SCB107-180 SCB107E-180
18 METERS CASSEGRAIN EARTH STATION ANTENNAS
3
C o n t e n t 1 General………………………………………………………………………………...2 2 Technical Specifications………………………………………………………………3 2.1 Specifications of the model SCB37-180…………………………………………….3 2.2 Specifications of the model SCB107-180…………………………………………...4 2.3 Specifications of the model SCB107E-180………………………………………….5
3 Structural Character and Operational Principle………………………………………..6 3.1 System Structural Character...................................................................…..................6 3.1.1 Antenna Structural Character..………………………………………….……….7 3.1.2 Antenna Pedestal Structure…..…………………………………………………13 3.1.3 Feed Structure…..………………………………………………………………15
3.2 Antenna Operation Principle..................................................................................... 17
4 Maintenance..............................................................................................................….17
4.1 Operation and Maintenance of Antenna.............…............ .....................…............. 17 4.2 Operation and Maintenance of Servo Equipment......................................…............ 20
2
1 General
The 18m antenna, a synthetic Cassegrain dual-reflector antenna models SCB37-180,
SCB107-180 and SCB107E-180, adopts some new technologies, such as high-performance
corrugated horn and broadband microwave network, etc.
The antenna performance meets the requirements of ITU-R/ITU-T、INTELSAT IESS-207 and
Resolution 572 of Anatel standards. It is not only provided with many excellent electric
performances, such as high efficiency, low sidelobe, low cross polarization, low Voltage
standing waves ratio (VSWR), high G/T value, but also with excellent characters including
appropriate structural design, strong wind resistance ability, beautiful appearance and high
tracking accuracy. It is a new generation satellite communication antenna.
This manual is applicable for the follow models of antenna:
SCB37-180: C-Band Cassegrain 18 meters antenna for Circular or Linear Polarization;
SCB107-180: Ku-Band Cassegrain 18 meters antenna for Linear Polarization;
SCB107E-180: Extend Ku-Band Cassegrain 18 meters antenna for Linear Polarization;
3
2 Technical Specifications
2.1 Specifications of the model SCB37-180:
Electrical Performance 3625 to 4200 MHz
Frequency Range Tx 5850 to 6425 MHz
Polarization Linear or Circular Rx 55,7 dBi (@ 4,00 GHz) Gain
(Including Losses) Tx 59,2 dBi (@ 6,00 GHz) Rx 0,3º (@ 4,00 GHz)
Half-power Beamwidth Tx 0,2º (@ 6,00 GHz)
10º El 42 K (@ 4,00 GHz) 20º El 36 K (@ 4,00 GHz) Noise Temperature 30º El 33 K (@ 4,00 GHz)
Typical G/T, 20º elevation at clear Sky with C Band LNA, 30 K
37,3 dB/K (@ 4,00 GHz)
Anatel Resolution 572 FCC regulation 25.209 Radiation Pattern Envelope
ITU-RS580 Rx 1.06 (0,5 dB) Axial Ratio
(Circular Configuration) Tx 1.06 (0,5 dB) Rx 35 dB Cross Polarization Discrimination
(Linear Configuration) Tx 35 dB Rx 1.3 (17.7 dB)
VSWR (Return Loss) Tx 1.3 (17.7 dB)
TX/RX 75 dB Port to Port Isolation
RX/TX 55 dB Rx CPR 229G
Feed Termination (flange) Tx CPR 137 G
Input Maximum Power 2000 W
Mechanical Characteristics Diameter 18 meters
Antenna Geometry Cassegrain Motion Elevation over azimuth
Azimuth ± 90º Elevation 0 a 90º Motion Adjustment
Polarization ± 50º Reflector Material Aluminum Mount Material Steel
Reflector White painting Finishing
Mount Hot dip galvanized Surface Precision 0.5mm (RMS)
Environmental Characteristics Operational Wind 130 km/h
Survival Wind 198 km/h Shock and Vibration Typical in sea, air and terrestrial shipments
Atmosphere Found in seashore and industrial areas
4
2.2 Specifications of the model SCB107-180:
Electrical Performance 10700 to 12750 MHz
Frequency Range Tx 13750 to 14800 MHz
Polarization Linear Rx 65,2 dBi (@ 12,00 GHz) Gain
(Including Losses) Tx 66,5 dBi (@ 14,00 GHz) Rx 0,10º (@ 12,00 GHz)
Half-power Beamwidth Tx 0,09º (@ 14,00 GHz)
10º El 60 K (@ 12,00 GHz) 20º El 50 K (@ 12,00 GHz) Noise Temperature 30º El 46 K (@ 12,00 GHz)
Typical G/T, 20º elevation at clear Sky with C Band LNA, 60 K
44,3 dB/K (@ 12,00 GHz)
Anatel Resolution 572 FCC regulation 25.209 Radiation Pattern Envelope
ITU-RS580 Rx 35 dB
Cross Polarization Discrimination Tx 35 dB Rx 1.3 (17.7 dB)
VSWR (Return Loss) Tx 1.3 (17.7 dB)
TX/RX 75 dB Port to Port Isolation
RX/TX 55 dB Rx WR 75
Feed Termination (flange) Tx WR 75
Input Maximum Power 1000 W
Mechanical Characteristics Diameter 18 meters
Antenna Geometry Cassegrain Motion Elevation over azimuth
Azimuth ± 90º Elevation 0 a 90º Motion Adjustment
Polarization ± 50º Reflector Material Aluminum Mount Material Steel
Reflector White painting Finishing
Mount Hot dip galvanized Surface Precision 0.5mm (RMS)
Environmental Characteristics Operational Wind 130 km/h
Survival Wind 198 km/h Shock and Vibration Typical in sea, air and terrestrial shipments
Atmosphere Found in seashore and industrial areas
5
2.3 Specifications of the model SCB107E-180:
Electrical Performance 10700 to 12200 MHz
Frequency Range Tx 12750 to 14500 MHz
Polarization Linear Rx 64,8 dBi (@ 11,45 GHz) Gain
(Including Losses) Tx 66,2 dBi (@ 13,50 GHz) Rx 0,10º (@ 11,45 GHz)
Half-power Beamwidth Tx 0,09º (@ 13,50 GHz)
10º El 60 K (@ 11,45 GHz) 20º El 50 K (@ 11,45 GHz) Noise Temperature 30º El 46 K (@ 11,45 GHz)
Typical G/T, 20º elevation at clear Sky with C Band LNA, 60 K
43,90 dB/K (@ 11,45 GHz)
Anatel Resolution 572 FCC regulation 25.209 Radiation Pattern Envelope
ITU-RS580 Rx 35 dB
Cross Polarization Discrimination Tx 35 dB Rx 1.3 (17.7 dB)
VSWR (Return Loss) Tx 1.3 (17.7 dB)
TX/RX 75 dB Port to Port Isolation
RX/TX 55 dB Rx WR 75
Feed Termination (flange) Tx WR 75
Input Maximum Power 1000 W
Mechanical Characteristics Diameter 18 meters
Antenna Geometry Cassegrain Motion Elevation over azimuth
Azimuth ± 90º Elevation 0 a 90º Motion Adjustment
Polarization ± 50º Reflector Material Aluminum Mount Material Steel
Reflector White painting Finishing
Mount Hot dip galvanized Surface Precision 0.5mm (RMS)
Environmental Characteristics Operational Wind 130 km/h
Survival Wind 198 km/h Shock and Vibration Typical in sea, air and terrestrial shipments
Atmosphere Found in seashore and industrial areas
6
3 Structural Character and Operational Principle
3.1 System Structural Character The 18m full-motion antenna system is composed of antenna feed subsystem and structure
subsystem. The antenna feed subsystem contains feed and main reflector and subreflector
curves. The structure subsystem contains main reflector and subreflector, polarization rotation
device, pedestal and antenna feeder. The composition principles of antenna system are shown
in Fig.3.1-1. The picture is shown in Fig.3.1-2.
Fig.3.1-1 Composition Principle Block Diagram of Antenna System
7
Fig.3.1-2 Picture of 18m antenna 3.1.1 Antenna Structural Character
3.1.1.1 Antenna Reflector Assembly
The antenna reflector is mainly composed of main reflector, subreflector, backups,
subreflector supporting device, feed sleeve, etc. The three-dimensional forming diagram is
shown in Fig.3.1-3.
8
Fig.3.1-3 Structural Schematic Diagram of 18m Antenna
3.1.1.2 Main Reflector Design
The main reflector is one of the core components of the antenna system. Its theoretical curved
surface is formed by synthetic curve rotating around the axis of the antenna. The antenna
reflector is divided into multiple plates because of cumulative materials, manufacturing
engineering, final assembly adjustment, etc. The reflector is divided into four rings. Inner ring
reflector is divided into 16 same sector panels and the rest are divided into 32 sector panels.
So the main reflector of antenna is composed of 112 panels.
The stretched and shaped 2A12-O aluminum board with thickness of δ=2mm is used as
individual sector plate after quenching, stretching and shaping. Z type aluminum casting
material is used as back rib after quenching, stretching and shaping in order to perform
positioning with rivet the die table for riveting rib and reflector. Each sector plate is supported
at backups via 6 stretching bolts. In order to ensure the process precision, such process
technology as first bonding and second riveting is adopted to improve the strength of
individual plate and reduce the number of rivets and thus decrease the local deformation of
plate caused by riveting points. The high precision mould and tool set up process are used for
all procedures, such as stretching, stretch bending, riveting. The accuracy of the individual
plate is ≤0.25mm (R.M.S). The reassembly precision of whole main reflector is ≤0.45mm
(R.M.S).
9
3.1.1.3 Subreflector and Its Supporting Mechanism Design
The subreflector is made of aluminum casting material and adopts the integral structure. It is
manufactured with the numerically controlled machine tool to ensure its precision, which is
not more than 0.15mm (R.M.S). The subreflector supporting mechanism is composed of four
support rods and one adjustment mechanism. In order to reduce its shadow to the main
reflector and ensure the supporting rigidity, the subreflector support rod adopts the flat oval
steel tube, of which one end is supported at the main backups and the other is connected with
the subreflector through adjusting mechanism. The four adjusting bolts of adjusting
mechanism are used to implement the adjustment of subreflector axial movement, lateral
movement and drift angle. The three-dimensional forming diagram of subreflector and its
supporting mechanism is shown in Fig.3.1-4.
Fig.3.1-4 Three-dimensional Diagram of Subreflector and Supporting Mechanism
10
3.1.1.4 Reflector Backups Design
The backups are the main stressed component and structural support of the whole antenna
reflector. It adopts space reticular truss structure, of which various structural parts have such
advantages as goodish consistency, smooth stress transmission, uniform stress, favorable
manufacture and installation, etc. and are widely applied because of the higher rigidity-weight
ratio.
The backups consist of the HUB, radiating beams and hoop stress bars and diagonal bars. It is
divided 32 pieces of main radiating beams along circumferential direction, a space pull bar is
laid between two radiating beams. The diagonal bars are laid between the outer surface
radiating beams. The previous bars parts constitute the space reticular truss structure, as
shown in Fig.3.1-5.
Fig.3.1-5 Reflector Backups Schematic Diagram
The HUB is the basic stressed component in the antenna structure and also the connection
component between the antenna reflector and antenna pedestal. All loads of antenna reflector
are down-transferred concentratively through the HUB. So the HUB must have higher
rigidity.
11
The appearance design of HUB is tapering barrel type, the bottom diameter is φ5500mm,
the height is 1910mm, the coning angle is 73°. The tapering barrel is made of steel plate (t=8),
the top and bottom (t=10) are seal-welded with flange. 32 heterotypic ribs are in the
corresponding positions of the HUB and radiating beams. All rings of concentric circular rib
plates with the height of 200mm are respectively at the top and the bottom, so the cellular
structure is formed in the whole HUB to make it have maximum rigidity. The polyphenyl heat
insulating material with thickness of 50mm is stuck in the tapering barrel of HUB to
constitute the high frequency room after built-in of fireproofing decorative plates for
installation of general equipment and high frequency receiving components, of which
minimum available volume is φ 5500 × 1910 and which has larger and comfortable
environment space. In order to meet the requirement of transportation, the HUB is designed as
bilateral symmetry connection type, the thickness of connection steel plate is 16mm, the
material type is Q235A, the fastener is M20 high intensity bolt, as shown in Fig.3.1-6.
The radiating beams is one of the main stressed components in the antenna reflector space
reticular truss structure. It is the planar truss constituted by top boom, low boom, normal web
member and diagonal web member through spherojoint welding. Its main role is to form the
supporting back bracket of the main reflector of antenna with hoop stress pull bar and
diagonal draw bar. The top boom and low boom are made of 20# steel material and they are
seamless steel tubes with size of φ 57 × 3. The normal web member and diagonal web
member are made of 20# steel material and they are seamless steel tubes with size of φ50×
3. Their characteristics are simple type, uniform stress, high rigidity and convenient surface
treatment, as shown in Fig.3.1-7.
Fig.3.1-6 Schematic Diagram of HUB
12
Fig.3.1-7 Schematic Diagram of Radiating Beams
The hoop stress pull bar is the steel pole fitting of φ50×3. The 3 hoop stress pull bars and
diagonal draw bars are connected from beginning to end to the outer end of the radiating
beams to play the role of hoop stress stabilization for the reflector framework. The material is
20# steel.
3.1.1.5 Feed Sleeve
The feed sleeve is the supporting component of feed network, which is divided into two
segment such as upper segment and lower segment. Both are formed through rolling and
welding of Q235A steel plate with thickness of 4mm. The lower segment uses circular sleeve
structure and moving sleeve design, microwave network is installed in the moving sleeve,
which performs moving connection with fix sleeve through two thin wall bearing, the fix
sleeve is fixed in the HUB. The upper segment uses tapering sleeve structure, of which the
upper end surface performs positioning connection with corrugated horn and the lower end
surface performs positioning with the rabbet of moving sleeve and the flanges are connected
with bolts. So, the linear polarization direction of feed network can be adjusted only by
rotating moving sleeve for implementing linear polarization surface adjustment which uses
electric mode.
13
3.1.2 Antenna Pedestal Structure The antenna pedestal adopts the elevation over azimuth full-motion mount structure, mainly
composed of azimuth king-post, azimuth box, elevation box, left/right support arms, elevation
lock device, azimuth/elevation driving device, azimuth/elevation bearing, operation platform
and ladder, etc. The structural three-dimensional modeling view is shown in Fig.3.1-8.
Fig.3.1-8 18m Antenna Pedestal 3D Modeling View
3.1.2.1 Azimuth Part The azimuth part mainly consists of azimuth king-post, azimuth box, large azimuth bearing,
azimuth driving device, cable winding device, limit and angle measuring device, etc. The azimuth drive uses dual drive chains and electric anti-backlash drive. The azimuth
king-post and turntable use steel plates that are welded into cavity structure, there is large
space in the inner cavity where the driving system, cable winding device, limit and angle
measuring device and lock device, etc. are placed. The azimuth rotation range is within ±165º.
14
3.1.2.2 Elevation Part The elevation part mainly consists of elevation box, left/right support arms, driving system,
limit device and angle resolver device, buffer, lock, counterweight and operation platform and
ladder, etc. The elevation drive also uses dual drive chains and electric anti-backlash drive. The elevation
box and left/right support arms use steel plate welded structure. The elevation rotation range
is within 0º~90º.
3.1.2.3 Driving Device
The driving device is used for driving the antenna to align satellite. The antenna driving
system is divided into two parts i.e. azimuth driving device and elevation driving device. The
azimuth driving device and elevation driving device have the same composition, both use
dual-motor clearance driving mode, and have dual drive chains, each of which consists of
motor, planetary gear decelerator and final-stage large gear. The method of using dual drive
chains has the following advantages: using electric anti-backlash drive method to eliminate
backlash and improve the system point and track precision, at the same time, reducing the
volume of driving box and increasing the rigidity of driving system. The driving device composition is as shown in Fig.3.1-9.
Fig.3.1-9 Block Diagram of Driving Device 3.1.2.4 Synchronization Device
The synchronization device transforms the rotating angles of axes into the electrical signals
and obtains the position information of antenna. It is mounted on the azimuth and elevation
axes of antenna by using sleeve shaft mode so as to meet the requirements of information
transmission and transformation.
15
3.1.2.5 Limit Device
In order to make the antenna rotate within the safe range, install safe limit protection device
on the azimuth and elevation axle heads of antenna to make the antenna operate safely.
The limit device consists of the limit switch and mass. The limit swicths are respectivily
installed on the two extreme positions of travel range of azimuth and elevation axes, when the
antenna travels the extrem position and the mass touches switch, the power supply is switched
off.
3.1.2.6 Platform and Ladder
For the convenience of maintenance and ensuring safeguard, the guardrail, ladder and
platform are installed on the antenna pedestal.
3.1.3 Feed Structure The feed is the core of the whole antenna and its performances directly affect the RF
performance of the antenna. So the optimized scheme and design should be performed more
carefully. The feed is composed of corrugated horn and microwave network.
3.1.3.1 Corrugated Horn
Rx and Tx singles of the antenna share the same corrugated horn. It’s required to realize
ideal radiation at the Rx and Tx bands, with rotary symmetry and low cross polarization
radiation pattern and low VSWA characteristic.
The corrugated horn consists of input taper section, mode converter section, transition
section and output flare section. The transition section may include frequency transition
section and angle transition section. If the frequency band is narrow, there is no frequency
section. The principle block diagram is shown in Fig.3.1-10. The purpose of the mode
converter section is to well convert the main mode TE11 in the circular waveguide into the
main HE11 in the corrugated waveguide, at the same time, maintain good match and reject the
generation of the harmful high order mode EH12. The transition section is to accomplish the
transition of frequency and the angle between the mode converter section and the output flare
section, at the same time, reject the generation of the harmful high order mode EH12. The
output flare section is to generate the required subreflector brim illumination level. The mode
converter section is the key design. The ring-loaded slots in the mode converter section are
16
adopted to expand the frequency band. The structural figure of the whole horn in C-band and
Ku-band is shown in Fig. 3.1-11 and Fig. 3.1-12, respectively.
Fig. 3.1-10 Corrugated Horn Block Diagram
Fig. 3.1-11 Structural figure of corrugated horn in C-band
Fig. 3.1-12 Structural figure of corrugated horn in Ku-band
17
3.2 Antenna Operation principle
The C-band or Ku-band 16m Cassegrain antenna can be supplied with two ports (RX/TX) or
four ports (2TX/2RX). The operation principles are described as follows.
Antenna receiving principles:the antenna aligns satellite, the satellite signals are transmitted
via main reflector and subreflector to the feed, then output from the corresponding port of
feed and finally sent to the tracking receiver after LNA amplification.
Antenna transmitting principles: the transmitting signals are sent from HPA to the feed via
waveguide and radiated by the feed, then reflected to the free space via main reflector and
subreflector of antenna and propagated to satellite.
The antenna can simultaneously transmit and receive electromagnetic wave signals. The
step tracking mode (optional) is used to make the antenna be able to align the satellite.
4 Maintenance As outdoor equipment, the antenna is exposed to natural environment such as wind, rain and
sun. The life of the equipment is greatly affected by correct operation and maintenance.
High-quality maintenance in time is very important to guarantee the service life of the
equipment.
To ensure the service life of the outdoor equipment, follow the requirements described below
for operation and maintenance.
4.1 Operation and Maintenance of Antenna
a) Pay attention to the local weather forecast. When strong wind higher than 32m/s is
coming, make preparations in advance so as to lock the antenna toward the sky with pin
at any time.
b) Once the subreflector has been installed and adjusted well and put into use, nobody is
allowed to go up onto the subreflector support. If it is necessary to go onto it for
maintenance, it is prohibited to step on the subreflector to prevent the installation
accuracy of the subreflector from being changed.
18
c) The main reflector is made of aluminum plates. The maintenance person isn’t allowed to
wear shoes with hard soles to avoid damaging the main reflector.
d) Check regularly the thin seal film on the horn mouth surface. If there’s any leakage,
replace it in time or the normal operation of the antenna will be affected.
e) The feed network and wave-guide components adopt rigid connections. Impact and crush
are prohibited.
f) Paint regularly. Spray three-proofing paint onto the antenna once every three years.
g) Check if the components of the antenna have been installed correctly and reliably before
startup. Eliminate the fault symptoms in time if there’s any.
h) Check regularly the seal cover of the synchronization device and check if all connection
points of all cables are sealed. Seal the exposed part with sealant to prevent water leakage
which causes short circuit or makes the equipment burned.
i) When the antenna azimuth operation range changes and requires changing the section, it
is recommended the wind speed be Grade 1~2 and not exceed Grade 3~4 at most. The
position where the section is changed should enable the AZ leading screw to pass the
position of the front support rod of the tripod, that is at AZ 100°or 260°. Generally 4~5
persons are needed for section changing and one person takes command. The connector
bolts of 6 M30 AZ drive leading screws are taken down, then the AZ drive and the
antenna AZ are pushed to rotate to reach AZ 260°or 100° and connector bolts of 6 M30
AZ drive leading screws are reinstalled. j) Check and maintain the antenna pedestal regularly (three months is appropriate). Be
careful to cut off the power to ensure human and equipment Safety during routine check
and maintenance of the antenna pedestal. Make the following checks:
• Check regularly the AZ left and right limit the EL up and down limit.Remove the
failure in time if there’s any to prevent such cases as that the limit cannot function
when necessary, thus preventing serious accidents.
• Check regularly if the motor and the synchronization device are in good condition
and sealed to prevent open circuit or short circuit leading to accident.
• Check regularly if the exposed screws are fixed well and screw down the loose ones
in time if there’s any.
• Check regularly if the lacquer coat has been damaged. Paint the damaged coat in time
(with zinc chromate primer and white polyurethane enamel.
19
• Check frequently all structural parts and rotating parts (shaft, bearing, leading
screw, worm gear reducer, planetary reducer and cycloid pinwheel reducer). Resolve
the problem in time if there’s any.
k) Overhaul of Antenna Pedestal ( the equipment should be stopped, once every three years)
• Check if all parts and components are damaged. Replace the damaged one in time if
there’s any.
• Clean, derust and oil all moving parts to guarantee flexible movement.
• Clean and adjust the axis, bearing, leading screw, worm gear reducer, planetary
reducer and cycloid pinwheel reducer. Replace the damaged or nearly damaged
component in time and apply enough lubricant (the lubricant grease is MnS2 EP lithium
grease, the oil is high-grade heavy-duty gear oil) at the same time to ensure flexible
movement. The lubricant grease and oil should be filled as described in (q). The grease
and oil must be filled sufficiently, missing and inadequacy will cause serious results and
the moving parts will be damaged in short time.
• Painting: spray paint in an all-round way once every three years. Clean the original
lacquer coat before painting, then paint it with zinc chromate primer as required
(once to twice) and white polyurethane enamel (twice to three times as required).
l) There’re two levels of moving speed of the antenna: fast and slow. The fast level is used
for antenna section changing, stowing and satellite searching and the slow level for
tracking satellite in normal operation.
m) In case of natural disasters such as windstorm and earthquake, check the equipment
constantly and replace the damaged parts and components in time.
n) When the wind speed has reached the speed to stow the antenna, if extremely strong wind
above Grade 10 is forecast (consider the wind speed at that time according to the
forecast), rotate the antenna 2 hours in advance to the stowing position facing the sky.
o) The leading screw cover is used to protect the leading screw. If damaged, repair or
replace it immediately.
p) Check the shaft, bearing, leading screw, worm gear reducer, planetary reducer and cycloid
pinwheel reducer once every three months and apply lubricant (the grease is MnS2 EP
lithium grease, the oil is high-grade heavy-duty gear oil) at the same time to ensure
flexible movement. The method is:
• Apply lubricant grease to the AZ and EL reducer box. Take down the organic
glass plate from the box, then fill up with mushy lubricant mixed by MnS2 EP lithium
20
grease and high-grade engine oil.
• Smear the AZ and EL leading screw with MnS2 EP lithium grease. The method is:
open the leading screw protection cover and smear the leading screw thread surface
with grease uniformly.
• Fill the oil cups of the AZ and EL rotating axles with MnS2 EP lithium grease (or
mixed with high-grade engine oil to be mushy grease) using pressing oil gun to lubricate
the rotating axles.
• Lubricate the planetary reducer and the cycloid pinwheel reducer. The method is
to fill the grease hole with heavy-duty gear oil.
4.2 Operation and Maintenance of Servo Equipment
a) Don’t turn on and turn off the power switches frequently to prevent the components
inside the cabinet from being damaged.
b) Hot-plug is prohibited to prevent the equipment or peripheral components from being
damaged and prevent malfunction.
c) Be careful to set parameters in system menu. Don’t modify the parameters rashly.
Don’t modify the system parameters, check them regularly. Once they are found to
have been changed, restore them to the original value in time.
d) Hot-plug may damage the equipment.