Control Précis 1 Flashcards
What is NON-Coherent light
Light caused by photons emitted in random directions
Different frequencies
Out of phase
Different coloured light
What is Coherent light /
Monochromatic light
Light where the photons are directed and emits on the same frequency
Mono - Single frequency
Same colour
Same phase
What Light will the Ruby Crystal alone produce if white light alone was used
NON Coherent light
Describe how a
RUBY CRYSTAL LASER
Works?
White light stimulates ions to E3/4
Heat is given of & drops to E2
Red light is emitted from E2 down to E1
Coherent light increases at the rate ions fall E2-E1
Population inversion accurs
But diminishes due to ions falling faster than white light can pump them up to E3/4
White light has to stimulate the process over again resulting in low energy pulses
Explain what is
Q- Spoiling
Technique to produce high energy pulses
Rotating prism is used instead of a mirror
Only when the prism is in alignment can LASER start
White light is switched on 350uS before alignment, to establish POPULATION INVERSION
LASER light will be reflected in the MW for 100nS
Power originated from a high energy flash tube as the white light source
Name some
LASER SAFETY
Precausions
Never look into the LASER
Beware of reflected surfaces
Use special Glasses
Get your eyes regularly tested
Frequency oscillation formula
Fosc = C/2🔺R
🔺R - delta range
±5= -2.5 . +2.5. Range is 5
Range formula
Te = transmit / receive
R = CTe/2
On a TLS, how is the
Range formula
Calculated
It measures the distance by sending a Pulse (Td) out
and reading the Time delay (Te)
between the received pulse (Td) back
Range Resolution / discrimination
Formula
Tr = Period of / cycle set by the system
🔺R = CTr/2
On a TLS, how is the
Range Resolution/Distortion
Calculated
The accuracy/ resolution/ distortion is determined by the FREQUENCY of the oscillator measuring the Time delay (Te) between pulses
Higher freq = higher accuracy in (1 meter intervals)
±2m accurate
Lower freq = lower accuracy in (10 meter intervals)
±20m accurate
Target resolution / discrimination
Formula
Td = width of LASER pulse
R = CTd/2
On a TLS, how is the
Target Resolution/ Distortion
Calculated
IOT avoid Target discrimination, which is 2 returning pulses so close to each other they overlap and look like 1.
_n_ Instead of. _n_n_
Smaller Pulse width (Td) = less chance for return pulses to overlap
Te > Td
Higher pulse width (Td) = more change for return pulses to overlap
Te < Td
Tank LASER sight Min Range?
400 m
Tank LASER sight max range
10km
Why do we have a MIN range
Due to possible echoes that can reflect back and set off the counters
Giving false readings
What depends the MAX range for a Tank LASER
MAX range depends on the power of the received signal back
As range increases, the power reflected diminish until it cant be detected anymore. Which will be Max range
Pr = 2Pp.At.Al/Pi2.R4.02b
Why does spontaneous emissions produce NON-Coherent light
Because NON - Coherent light is caused by photons emitting light in random directions
On TLS
Why does the system require 2 counters?
Two required
One acts as a starting point where as the other one is reset when when a signal/ pulse is received back
Once the second ones counter is reset it counts to the end of its clock and switches everything off
The difference in counter readings will determine the distance
What is the function of the DUO-DIODE PUMP on the TLS?
Minimises noise and keeps the system amplified
What does the first/last switch do?
First - gives you a distance on the first pulse reading it receives back
Last - gives you a distance on the last pulse reading it receives back
With the aid of a graph explain the FIRST PULSE RANGING on TLS?
Draw a graph showing the 2 counters on a TLS with one lagging behind the other after receiving a Pulse echo, resetting and counting to 999 to shut everything down
Role of the 999 detector?
- Switches off the Rgate, stopping it from receiving any more pulses
- Switches off both counters when they reach 999, the difference being your distance
On TLS what are the first 3 thing that starts up?
P 1-18
(P 1-18)
- PFN
- System Dump 30sec
- Prism motor drive
What is Visual Acuity?
The ability for the eye to distinguish between two points
What is Raster scanning ?
The process to scan picture lines, line by line
What is INTERLACING?
Where a picture is scanned in two parts
- Scan odd lines first
- Scan even lines after
When both field pictures are scanned, its called one frame.
What is the difference between odd and even fields?
Interlacing takes place when
Odd fields gets processed first
Even fields gets Processed second
To make a full frame
CCIR Video signal
Lines?
Frames?
Interlace?
Sync
Lines - 625 lines
Frames - 25
Interlace - 1:1
Sync - Sync Negative
Name 2 Tv synchronisation types
LINE Sync
FIELD Sync
Describe what Line Sync is?
- All the horizontal picture lines, separated from each other by a Neg Pulse
Draw a typical Line Sync pulse
And name the stages?
P1-22
(P1-22)
Front porch 1.55us - allows receive circuitry to settle
Sync pulse 4.7us - sync pulse
Back porch 5.8us - Fly past
What is FIELD Sync?
Happens twice per frame
Once after the all the odd LINES were processed
Again after all the even LINES were processed
What does FIELD sync consist of?
Start…
5 Pre-equalising pulses
5 Field broad sync pulses
5 Post-equalising pulses
25 line Field blanking period
Repeat…
Draw a FIELD sync circuit?
Describe it…
(P 1-27)
(P 1-27)
LPF (low pass filter)
Denies LINE Sync pulses using the LPF, and allows through FIELD sync pulses
Remember( Low blocks Line)
Draw a LINE sync circuit?
Describe it…
(P 1-28)
(P 1-28)
HPF (high pass filter)
Denies FIELD sync pulses, but allows through LINE sync pulses
Remember(Low blocks Line)
Draw the Visual display unit
Describe the drawing in a few sentences?
(P 1-26)
(P 1-26)
- Composite video signal comes in and get separated by a SYNC separator (LPF/HPF)
- LINE sync pulses are smaller and more frequent than FIELD sync pulses!
- LINE/FIELD both go into their own Scan Oscillators which Saw Tooth their pulses/waves
- LINE pulse goes through a extra Pulse sharpener
- The Composite Video signal is amplified before going into the Picture tube
What is PIN CUSHIONING?
How can it be overcome…
Type of distortion in TV system which can be overcome using PERMANENT MAGNETS
What is EHT Generation?
Draw a diagram (P1-32)
(P1-32)
- The screen needs high Voltages to operate
- Using already available LINE sync signals we can increase the Voltages desired by using a Diode multiplier
- During a Pos(+) cycle D1 conducts and charges C2
- During a Neg(-) cycle / FlyBack C1 charges from C2
- Next Pos(+) cycle D3 conducts and charges C3
- Next Neg(-) cycle / FlyBack C4 charges from C3
- Hence the charge is pumped resulting in a 3X voltage increase
How does a CRT scanning work?
(P1-29) Figure.7
(P1-29) Figure.7
- Scene of view is focused onto a screen
- an Electron beam scans the screen
- The scanning is subject to different patterns of light causing more/less current flow
- The change in current flow will be detected by the resistor
- Which forms the Picture information in the form of a video signal
a) What does equalisation pulses do?
b) What do post sync pulses do?
a) Ensure the video signal equalises and does not interfere with interlacing
b) Adds a blanking period allowing adequate time for completion of field flyback.
Minimum and maximum range of a TLS ?
Max 10,000m
Min 400m
Explain the function of the Sync Seperator
P1-26
(P1-26)
Sync separator separates the LINE/FIELD sync from the composite video signal
Describe what the composite video signal is made up of.
And the process used to separate the signals once detected?
Negative going LINE/FIELD sync pulses.
Process is to use a LPF and HPF to separate the LINE and Field sync
Night surveillance may be obtained how?
Active Illumination (AI) - active
Low light Television (LLTV) - cws sight / passive
Thermal Imaging (TI) - passive
State a method for Active Illumination?
Illumination of infrared light source
Active system, prone to detection
Low Light Television (LLTV)
Disadvantages?
CWS sight(passive) - which amplifies low light
- Insufficient on very dark night
- Too sensitive for daylight use
- Limited range
Thermal Imaging
Disadvantages?
Advantages?
Passive system that picks up infrared radiation from all bodies higher than ZERO degrees.
Disadvantages:
- Thick fog or clouds can absorb our thermal image depending on how hot our target is
Advantages:
- Operates on Darkest night
- Good in Daylight
- Good range
- good in light haze/mist/smoke
How does the weather effect the thermal imaging
Rain ,light haze mist and smoke has little effect on our thermal image
Thick fog or clouds can absorb our thermal image depending on how hot it is
What is EMISSIVITY?
The Radiative Efficiency of a surface compared to a black body.
Name the Thermal imaging term for the radiative efficiency of a surface compared to other surfaces?
Emissivity
Name the requirements for a TOGS Lens?
- Refractive Index (High)
- Temperature Sensitivity (Low)
- Hard surface (prevent abrasion)
- Mechanical strength (prevents cracking)
- Highly Transparent (related to wanted freq range)
How is REFLECTIVITY a bad thing for a Lens?
When photons strike a medium (lens), the energy might get reflected known as the
REFRACTIVE INDEX
Higher index = less photons absorbed
to go into the lens and give a picture
Can overcome this by a Technique called BLOOMING
What is BLOOMING and why is it used on a lens?
Blooming is a technique used to minimise the reflectivity of a lens.
On our Germanium lens a thin coating of Selenium is added
Germanium/selenium is in anti phase with the selenium/air interface canceling each other out
Improving the transmissivity (Photons passing through the lens)
What is Optical A-Thermalisation and how can it be overcome?
The De-focussing of a lens due to temperature changes and the expanding & contraction of the lens
Compensate for changes in Temp by:
- Manual adjustments
- Auto servo adjustments
How do we detect Thermal radiation?
By using a DETECTOR
Cadmium mercury telluride (Cd Hg Te)
Why and how is the DETECTOR cooled?
By cooling the detector we dramatically reduce the noise which can mask our signal to acquire a thermal image
Using a:
JOULE-THOMPSON MINI COOLER
Draw a diagram for the JOULE-THOMPSON MINI COOLER
And explain how it works?
P 2-11 (Figure. 8)
P 2-11 (Figure. 8)
- Detector (Cd Hg Te) is mounted in a vacuum tube
- High pressure (HP) Pure air is forced down a CRYOSTAT
- At the end of the cryostat is a tiny ORIFICE releases the air and allows it to expand
- Creating very low temperatures and cools the Detector
Draw and explain via a Diagram
REMOTE DISPLAY
P 2-16 (Figure. 14)
P 2-16 (Figure. 14)
Name 2 types of THERMAL IMAGER COMMON MODULE (TICM)
CLASS 1
CLASS2
TICM
What is a CLASS 1 and CLASS 2 intended for?
CLASS 1:
- DIRECT viewing
- Batt powered using high powered gas for cooling
CLASS 2:
- INDIRECT viewing
- High pressure gas cooled
- Display remote from TPU
Draw a typical MRTD curve
P2-20
P2-20
MRTD-Minimal RESOLVABLE temperature differeance
Normally 0.1 degree C
Draw and explain a typical MDTD curve?
P2-21
P2-21
MDTD-Minimal DETECTABLE temperature difference
What is being tested by the MRTD test?
Tests for the MIN RESOLVABLE TEMP DIFFERENCE between two adjacent elements
What is being tested by the MDTD test?
Tests for the MIN DETECTABLE TEMP DIFFERENCE between a target and its surroundings
