Marconi Instruments P4428 Technical Manual

8720A-4

Technical

Manual

THERMAL CAMERA

P4428

© Marconi Applied Technologies Limited

This report, which is released on the
understanding that the Company’s
proprietary rights therein are recognised
and that it is solely for the information of
the recipient, must not be copied either as
a whole or in part, or disclosed to any
third party or used as the basis for the
manufacture or sale of apparatus, without
prior written permission from the Company.

CONTENTS

FRONT FOLD
Section 1 General Descriptions Page

Picture of Complete P4428 1
Brief Specification 2 - 4
Operating and Technical Descriptions 5 - 13
Internal Assembly Details 14 - 18
Batteries 19 - 23
Camera Disassembly and Tube replacement 24 - 25
Modification Record 26 - 27

Section 2 Fault Finding and Setup
Primary Fault Check Procedures 28 - 32

Camera Electrical Set -Up 33 - 35

REAR FOLD
Section 3 Diagrams

Block Diagram 1
Circuit Diagrams and Layouts :

1) Scan and Monitor Board (Old & New) 2 - 6

2) Video Processing Board (Old & New) 7 - 10

3) Voltage Regulator Board (Old & New) 11 - 14
Parts Lists

Scan and Monitor Board (Old & New) 15 - 21
Video Processing Board (Old & New) 22 - 28
Voltage Stabiliser Board (Old & New) 29 - 31
Voltage Stabiliser Unit (Old & New) 32
Chassis 33
Yoke Assembly 34
Front Plate Assembly 35
Case 36
Battery Cartridges 37
Battery Substitution Unit 38
Accessories 39

Section 4

Detailed Fault Checklists 40 - 60
Waveforms 61 - 71

- 1 -

P4428 Pyroelectric Vidicon Camera

Complete with Voltage Stabiliser Unit

Specification

- 2 -

SPECIFICATION

1. Camera

The camera has been designed to operate in the hostile conditions
encountered in a fire-fighting environment.

Weight 3.0Kg (camera including muff and harness)
Material Case - Polycarbonate
Harness - Nylon
Muff PVC/Nylon flame retardant - felt liner
Visor Neoprene
Immersion The camera will withstand driving spray and total

immersion in water.

Case Sealing A test valve is provided so that sealing tests may

be executed using a vacuum pump.

A vent is also included which releases at an

internal excess pressure of 7 p.s.i.

Electrical
Power 3.7W Nominal

Voltage range 8.7V D.C. input
Battery life 10 size AA alkaline disposable cells - typically 2

hours.

10 size AA Nickel Cadmium rechargeable cells -

typically 1 hour.

(Note: rechargeable cells may need to be fully

cycled a few times to achieve maximum charge
capacity.)

Video The external video signal is nominally 1 Volt 625

lines 50Hz (CCIR compatible) or 525 lines 60 Hz
75Ω termination set at manufacture.

Specification

- 3 -

Temperature Resolution
200 lines per picture height for a temperature difference of 2EC (Chopped) -

1EC (Panned).
Lens
The lens has a hard anti -reflection coating and may be cleaned as necessary

with an appropriate soft cloth.
Focal length 18mm, f/0.8

Angle of View 57E
Spectral Response 8 to 14µm

P8092 pyroelectric vidicon PEVICON manufactured by Marconi Applied
Technologies Limited.

Electromagnetic Compatibility CE
The camera and VSU of cameras serial number above 6000 comply with the

requirements of EU directive 89/336 EEC.

Specification

- 4 -

2. Voltage Stabiliser

Mechanical

Weight 0.5Kg (less batteries)
Material Polycarbonate

Electrical
Input 9.5 to 15 volts

Output 8.7V @ 400mA D.C.

P4428K Voltage Stabiliser

Operating and Technical Descriptions

- 5 -

P4428 GENERAL DESCRIPTION
The P4428 hand -held thermal imaging camera uses the P8092 pyroelectric

vidicon, and provides a thermal television picture in the 8 to 14 micron
radiation band. It is enclosed in a sealed injection moulded polycarbonate
case and is intended for use in fire-fighting applications. The camera is a self
contained unit with a wide-angle germanium lens, giving a viewing angle of 57
degrees, with an integral viewfinder/monitor. The camera is fully automatic
with operation selection of 'Panned' or 'Chopped' mode of operation. Power is
provided by a reloadable battery cartridge which fits into the voltage stabiliser
unit attached to the camera harness. A video output socket is provided for
remote surveillance.

Where difference exist between the versions of camera those for the surface

mount board set (SMT) are given in square brackets [................].

1. ELECTRICAL SPECIFICATION

1.1. Power Requirements

The equipment requires a 9.3 to 15 volt supply at approximately 0.4
amps. A battery cartridge is provided which uses 10 standard 'AA' size

1.5 volt disposable alkaline cells.∗ The output from this pack is 15 volts
nominal and is regulated to 8.7V and current limited to 700mA by the

voltage stabiliser unit. At least 1.5 hours operation is possible on each
set of batteries. For use with external power supplies an adaptor is
available.
Alternatively 10 rechargeable AA cells (type NCC-50) may be used
with a reduced operating time of approximately 1 hour, depending on
cell capacity.

∗

See also Appendix 1.

1.2. Video Output
Composite video is supplied to an internal viewfinder/monitor. A BNC
video output socket is provided for an external monito r. This requires a
75Ω termination. Circular blanking is added to obscure edge effects of
the over-scanned target.

1.3. Performance
In the panned mode the temperature resolution at the centre of the field

of view is less than 0.5EC differential scene temperature at a spatial
resolution of 100 TV lines and better than 0.2EC at 20 TV lines,
assuming unity emissivity. (See also P8092 data sheet).

Operating and Technical Descriptions

- 6 -

2. MECHANICAL SPECIFICATION

2.1. Dimensions

Camera: 27cm x 17cm dia. (excluding pistol grip and visor)
Voltage Stabiliser Unit: 18cm x 6.5cm x ll.5cm

2.2. Weight
Camera: (including harness, muff, visor and pistol grip) 3.0kg

Voltage Stabiliser Unit: (less batteries) 0.5kg

2.3. The camera case comprises a two part polycarbonate moulding
retained by a breech type locking ring.

The voltage stabiliser unit is a polycarbonate moulding.

3. OPERATING MODES
The signal is proportional to the rate of change of the temperature of

the pyroelectric target and decays within 10 seconds of exposure. To
obtain a continuous signal from a stationary object a shutter is used to
obscure the target at field rate. Alternatively the image - or camera ­may be moved or panned.

3.1. Shutter
A rotating shutter is incorporated into the front of the camera. It is
synchronous in rate and phase with the camera scanning beam. The
images obtained are alternately inverted in polarity. They are
synchronously re-inverted and balanced in the video channel to give
continuous positive images. Shading correction circuits aid balance
between the signals and minimise flicker.

4. LINE FLYBACK GAS PEDESTAL
The ion pedestal within the tube is enhanced by increasing the beam

current during line flyback, i.e. by pulsing Gl positively. By this means a
larger signal is obtained from the tube. An automatic circuit detects and
regulates the ion pedestal.

5. OPERATING PROCEDURE
Plug the battery cartridge into the voltage stabiliser ensure the

connection between the stabiliser and camera is made, then switch on.
A satisfactory operating voltage is confirmed by observing that the
LEDs in the viewing window illuminate. A circular image will now be
obtained after a target discharge period and the camera chopped or
panned operating mode may be selected as required.

Operating and Technical Descriptions

- 7 -

6. COMPLETE SET UP FOR NEW TUBE

6.l. Replacing Tube

See Appendix 2.

6.2. Gl and Pedestal Control Adjustments
These controls are adjusted using the values of I G4 (BEAM) and I G4
(BEAM + PEDESTAL) pre-determined for each tube during factory test
to obtain a specific value of pedestal current. Using the jack lead and a
micro-ammeter, plug the jack into the Ig4 socket (Scan board). Turn
the pedestal amplitude control (Scan board RV110), fully clockwise
[anticlockwise SMT boards] for minimum Ig4; adjust the G1 control
(Scan board RV111), for recommended I G4 (BEAM) value and then
increase the reading to the recommended I G4 (BEAM + PEDESTAL)
value using the pedestal amplitude control.

Typical Values: I G4 (BEAM) = 4µA

I Gg4 (BEAM + PEDESTAL) = 11µA

Alternatively if relevant figures are not available for the tube, firstly
adjust IG4 current for 4µA as instructed in the previous paragraph.
Monitor the head amplifier output voltage on an oscilloscope and adjust
the pedestal control for a forward line scan pedestal of 175mV.

NB The I G4 (BEAM + PEDESTAL) value can be noted for future
reference.

6 3. Picture Acquisition

An image will normally be obtained with the camera controls
undisturbed from the previous tube. Set the camera to 'pan' mode.
Turn the circular blanking control slightly anticlockwise to display the
entire target image. Adjust the line and field shading pre-sets for
minimum shading either by inspecting the picture or preferably by
displaying the relevant field/line video waveforms on an oscilloscope.
Adjust for minimum shading using the parabola and tilt correction
waveforms. Switch to 'chop' and cover the lens. The black level control
may now be adjusted for a signal level of 1.5V on the oscilloscope.
This provides optimum range for the output level clamp. Shading may
sometimes be further improved by re-orientating the tube for minimum
symmetrical shading. If this is necessary the picture acquisition section
will have to be repeated.

Operating and Technical Descriptions

- 8 -

7. OPERATING FACILITIES AND ADJUSTMENTS

7.1. Electrode Supplies

Pre-set controls are located on the scan board.

i) G2 Fixed voltage 175 volts
ii) G3 Pre-set for 80 volts (RV109)

iii) G4 Fixed voltage 135 volts

iv) G1 Variable from 0 to -60 volts (RV111)
v) Target (CPS) Pre-set to 0 volts

7.2. 8.7 Volt Supply
This basic supply is pre-set in the voltage stabiliser unit (VR400 [VR1]).

7.3. Magnetic Focus
The control is located on the scan board (RV116).

NB The magnetic focus control should be used to adjust the tube
electrical focus in preference to varying G3.

7.4. Line Linearity
A saturable reactor is used to control the line linearity and width. It is
located on the scan board (L100). [SMT version requires turns to be
adjusted]

7.5. Scan Adjustments

The following controls are provided:
horizontal shift RV101; vertical amplitude RV112; vertical shift RV113.

7.6. Video Adjustments
Set the alignment controls (RV102, RV103 scan board) for even target

illumination and adjust the shading and black level controls (video
board) as covered in the picture acquisition section 6.3.

7.7. Circular Blanking
To increase the signal out of the tube it is usual to overscan the target.

This also prevents charging of the unscanned portion of the TGS
crystal. The edges of the resultant circular picture have bright
highlights. A circular blanking generator is provided whose output is
used to gate the video waveform. By adjusting the 'size' control the
unwanted video can be masked, (RV206, video board). The shape of
the circle is adjusted by a pre-set control on video board (RV207). The
shift controls may be used to centre the target image.

NB Correct circular blanking is essential for automatic video balance
and iris function.

Operating and Technical Descriptions

- 9 -

7.8. Flicker Suppressor
The flicker suppressor is a digital field store, used to eliminate flicker

between alternate fields in 'chop' mode. Adjustments are provided for
clock frequency (RV209), RAM input-output data phase (RV210) [not
required on SMT version], alternate-line interlace (RV212) and store
vertical position (RV211). No adjustment of these should be necessary
during setting-up. The balance control RV208 may be used to minimise
flicker in the 'chop' mode.

7.9. Output Video Level Clamp
Because the video signal is proportional to rate of change of
temperature and decays within a few seconds, unwanted changes in
black level can occur if the camera is moved after the signal from
objects in the field of view has decayed. In order to maintain a suitable
black level, an automatic circuit detects the coldest signal in the scene
and maintains its level 300mV above blanking level, in order that
details in cold objects can be seen.

8. CIRCUIT DESCRIPTION

8.1. The Synchronising Generator (Video Board)

The sync generator uses a RCA integrated circuit type CD22402,
which is locked to its own 500kHz crystal oscillator. Conversion from
625 lines 50Hz to 525 lines 60Hz is possible by opening the solder link
between pin 18 and 19 of the integrated circuit.

8.2. Video Head Amplifier
The head amplifier is located on the video board and is a high gain, low

noise amplifier with a nominal bandwidth of 5MHz (6dB). The cascade
input stage utilises a J309 FET which has a low input capacitance and
a high Yfs. The LM733 [NE592] amplifier compensates for the falling
input frequency response by incorporating a capacitor which bypasses
its feedback loop. The output is then passed to the main video
amplifier.

8.3. Video (ion Pedestal Stabilisation)
The video signal is clamped by Q210 [TR3] and then taken via P200/18
to the scan board where the unwanted positive pedestal portion of the
waveform is removed. The remaining negative pedestal is compared
with the reference voltage on RV110 (the pedestal drive control) and
the resultant output defines the voltage to which the G1 grid is switched
during the line flyback period. Hence the ion pedestal is maintained
against changes in the tube characteristics.

Operating and Technical Descriptions

- 10 -

8.4. Video Processing
Two stages of amplification are used with a combined gain of

approximately 25. The first stage utilises an LM733 [NE592] video
amplifier which has a gain of 5 and also acts as a phase splitter giving
outputs of both positive and negative phase. The video phases are
further amplified (x 5) and then recombined in a balanced video
selection, each phase being switched synchronously with a signal
derived from the shutter blade. Circular blanking is then added to the
video waveform before being passed to the flicker suppressor. Balance
between the two phases is achieved by comparing the signals in the
video averaging comparator, V204 [IC3], whose output acts on the
negative phase. A clamp pulse is produced from the line blanking
waveform using V106, delayed and timed by V202 [IC4], and used to
sample the video black level. The resulting signal is compared with the
required black level, set by RV204 (and RV200 in 'pan' [automatically
in SMT version]), in the comparator V204 and the feedback loop
completed by causing the comparator output to control the dc level in
the main amplifier V201. Shading correction signals are taken from the
circle generator and added to the black level circuit.
The video signal level varies between the pan and chopped modes of
operation. To correct this the shutter switch also modifies the channel
gain and black level by switching transistor Q204 [TR6] and resistors
R227, R228 and RV200 [R34, R35].

8.5. Circular Blanking Generator (Video Board)

The circle is produced using the principle of intersecting parabolas.
Line and field blanking waveforms are separately double integrated,
the first stage producing ramp waveforms and the second parabolas.
A crossing detector (V209) [IC12] then produces the circle which
operates on both positive (Q205)[TR8] and negative (Q206) [TR9]
video signals.
The shape of the circle is controlled by the field parabola amplitude,
RV207, and the size by applying a dc shift to the line parabola, RV206.
The ramp and parabolic waveforms are used for shading correction
and are added to the video signal via the black level circuit.

8.6. Flicker Suppressor (Video Board)

Flicker is removed by delaying one field of video information and
adding it to the next; thus the flicker, which inverts every field, is
cancelled and the signal, which is of the same polarity on all fields, is
doubled. In order to achieve the delay, the signal is digitised, written
into RAM, and read out on the following field. The data is then
converted to analogue form and added to the then present signal which
comes directly from the video input.
Meanwhile the present signal is digitised and written into the memory
location which has just been read to provide the delayed data. The
address then moves to the next location. A short delay (V211) is
needed in the direct path to balance propagation delays encountered in
reading the store.