Sentinel / Sentry Handbook
PPM INTELLIGENT FIBRE-OPTIC-LINK
SENTRY / SENTINEL IISC
TRx-HB-6
PPM LTD 2015
Contents
1
INTRODUCTION TO THE INTELLIGENT FOL RANGE .................................................. 1-1
THE TRANSMITTER MODULE .............................................................................................................. 1-1
THE RECEIVER MODULE .................................................................................................................... 1-1
FIBRE OPTIC CABLE ........................................................................................................................... 1-2
PRINCIPLE OF OPERATION .................................................................................................................. 1-3
2
INSTALLATION ........................................................................................................................ 2-1
SAFETY PRECAUTIONS ....................................................................................................................... 2-1
INITIAL INSPECTION ........................................................................................................................... 2-1
RECEIVER MODULE INSTALLATION .................................................................................................... 2-1
3
SETTING UP THE SENTINEL / SENTRY IISC FOLS ......................................................... 3-1
TRANSMITTER CONNECTIONS ............................................................................................................ 3-1
LEMO 3K FIBRE OPTIC CONNECTOR .................................................................................................. 3-3
RECEIVER CONNECTIONS ................................................................................................................... 3-4
4
CONTROLLING THE SENTINEL / SENTRY IISC FOL ..................................................... 4-1
USING THE SYSTEM CONTROLLER TO OPERATE THE SENTINEL / SENTRY ........................................... 4-1
SWITCHING ON THE SENTRY / SENTINEL IISC FOL ............................................................................. 4-2
SELECTING A MODULE ........................................................................................................................ 4-2
INPUT CHANNEL SELECT .................................................................................................................... 4-3
SETTING THE LINK GAIN .................................................................................................................... 4-4
CHANGING THE INPUT IMPEDANCE..................................................................................................... 4-4
TRANSMITTER TEST SIGNAL .............................................................................................................. 4-5
MAX INPUT DISPLAYED UNIT SELECT................................................................................................ 4-5
OPERATING THE SENTINEL IISC RECEIVER CALIBRATION FUNCTION ................................................. 4-6
5
REMOTE COMMANDS ............................................................................................................ 5-7
6
MAINTENANCE AND FAULT-FINDING GUIDE ................................................................ 6-1
7
SYSTEM SPECIFICATIONS .................................................................................................... 7-1
8
PRODUCT WARRANTY .......................................................................................................... 8-1
9
FIBRE OPTIC CONNECTOR CLEANING PROCEDURE .................................................. 9-1
10
SPARES INFORMATION ........................................................................................................ 2
PPM LTD 2015
Calibration Information
In order to guarantee optimum gain accuracy and passband flatness performance, your
Sentry / Sentinel IIsc system has been calibrated as a matched Transmitter/Receiver pair.
It is possible to use any Transmitter with any Receiver, but an additional allowance of ±0.5dB
gain uncertainty and ±0.5dB passband flatness should be made. The gain error caused by
using a non-matched Transmitter/Receiver pair is fixed, and can be compensated for by
normal measurement calibration routines.
The following Transmitter and Receivers have been calibrated as matched pairs:
Transmitter Serial Number
Receiver Serial Number
1
SN
SN
2
SN
SN
3
SN
SN
4
SN
SN
5
SN
SN
6
SN
SN
7
SN
SN
8
SN
SN
It is recommended that your Fibre Optic Link Modules be re-calibrated every 12 months to
ensure conformance to the published specification.
PPM LTD 2015
Safety Information
Please read the whole of this section before using
your new Sentry / Sentinel System.
Laser Safety
The light source within the Transmitter Module is a semiconductor laser diode of 1300nm
wavelength. The light is emitted from the optical connector on the Transmitter Module front
panel.
The laser radiation emitted from this product in normal use falls within the IEC825-1 CLASS 1
limit, and constitutes no hazard when used as recommended. Attention is drawn to the
following statements.
CAUTION
Use of controls or adjustments, or following procedures other than those specified
herein may result in hazardous radiation exposure.
CAUTION
The use of optical instruments with this product will increase the risk of eye hazard.
Electrical Safety
The PPM Test & Instrumentation System Subrack / Case that is used in conjunction with the
Sentry and Sentinel IIsc FOL is a Safety Class 1 instrument (it has a metal case that is
directly connected to earth via the power supply cable).

Hazardous voltages exist within the equipment.

Do not remove equipment covers when operating.

Make sure that only fuses of the required rated current, and of the specified type (antisurge, quick blow, etc.) are used for replacement.
Adjustment, maintenance and repair of the equipment should only be carried out by
suitably qualified personnel.
PPM LTD 2015
Important Handling Instructions
Connecting Lemo 3K Fibre Optic Connectors
Remove the protective dust cap from the cable mounted connector by holding the dust cap in
one hand, and pulling the connector out by its outer release sleeve with the other hand.
Remove the protective dust cap from the equipment by supporting the equipment with one
hand, and pulling the dust cap out with the other hand.
The 3K connectors are keyed and can only be inserted in one orientation. Correct alignment
is indicated by the alignment key-way and red alignment markings. The key/alignment mark
should be uppermost when the connector is being inserted.
The protective dust caps on the equipment and cable connectors should only be removed
immediately before the connectors are mated.
When the cable mounted 3K connector is inserted, it should be firmly pushed into the panel
mounted connector until the lugs are felt to latch into place.
Under no circumstances should the connector be forced into position.
Care should be taken not to drop the optical connector or to subject it to any other excessive
physical shock, particularly when it is not protected with the dust cap.
Disconnecting Fibre Optic Connectors
The connector is disengaged by a single straight axial pull on the outer release sleeve. This
first disengages the latches and then withdraws the plug from the socket.
Immediately after removing the connectors, all protective dust caps should be fitted.
Care of fibre optic connectors
When the fibre optic cables are not connected, it is essential that the cable and equipment
connectors are protected by the dust caps provided with the system. Failure to do so may
result in damage to the fibre ends, which are critical to the system performance.
System performance may be compromised by dirt on the connector end or its alignment
surfaces. Refer to section 9 for instructions on cleaning the optical connectors.
Connector performance will be compromised if the end face is scratched.
Heavy Items
Some parts of this product can weigh in excess of 2kg. For heavy or awkward items, ensure
that the correct precautions and safety equipment are implemented to avoid injury and/or
damage to equipment. If in doubt, consult your Health & Safety representative.
PPM LTD 2015
1 Introduction to the Intelligent FOL Range
The PPM Test & Instrumentation Intelligent FOL range is designed to meet the needs of
researchers and engineers whose work involves transmitting high bandwidth analogue
signals in electrically noisy environments, such as those encountered in EMP and EMC
testing.
The range comprises two FOL systems with similar functionality but different RF performance.
These are the Sentinel IIsc and Sentry IIsc. The Sentinel IIsc has an analogue bandwidth of
2kHz to >1GHz, while the Sentry has an analogue bandwidth of 40Hz to 600MHz.
Each system consists of a battery powered transmitter unit, which converts the input electrical
signal to an optical signal. This optical signal is transmitted down a fibre optic cable to a
receiver unit that recovers the electrical signal and also provides control of the transmitter
functions. Control signals are sent from the receiver to the transmitter via a second fibre. The
signal and control fibres are contained within a single ruggedised Fibre Optic Cable. A
calibrate circuit within the receiver module compensates for variations in optical loss of the
optical connectors in order to maintain system gain within the specified limits.
The Sentinel / Sentry IIsc Intelligent FOLs are the logical upgrade path from the Sentinel and
Sentry II, and enables the product to be compatible with the PPM Modular Test &
Instrumentation System. This includes the point2point range of modules.
The Sentinel and Sentry IIsc FOLs must be used in conjunction with the System Controller,
SCT-1.
The Transmitter Module
A typical transmitter configuration consists of two modules. These are : Transmitter Module containing the transmit RF pre-amplifier, attenuation blocks, laser
driver, laser diode module, power supply filtering/regulation and control circuitry.
 Battery Pack, used to provide electrical power to the transmit electronics.
The Transmitter Modules are designed for the maximum electrical screening possible given
the size and user flexibility constraints. Battery Packs are quickly and easily changed. This
enables the system to be operated continuously, with minimum delays whilst batteries are
charged.
The Receiver Module
The Receiver Module receives the optical signals from the Transmitter Module and converts
them back into an electrical signal. This is amplified and output on an SMA connector on the
Receiver Unit front panel.
The Receiver Module must be plugged into a PPM Case or Subrack containing a System
Controller before it can be operated. All receiver functions can be directly or remotely
operated using the System Controller. The Controller unit provides comprehensive control
features, which are easy to learn and use. A large, clear graphical LCD on the Controller and
indicator LEDs on the Receiver front panel provide the user with complete system status
information. During start up the system automatically detects which Receiver Units are
present.
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Fibre Optic Cable
A number of different types of fibre optic cable can be provided with the system. These are: Cross Site Fibre Optic Cables
A ruggedised Fibre Optic Cable that has a Lemo 3K optical connector mounted on both ends
of a multi-core, ruggedised cable. The connector is securely bonded to the cable.
Extension Leads
These may be used to extend the cross-site cable. For example, it may be required to have a
bulkhead connector at the wall of a test chamber or control room. These extension leads may
only be used as extension leads, and cannot be used in place of the cross site cable.
The Fibre Optic Cables and Extension are available in a range of lengths to suit individual
requirements.
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Principle of Operation
FOL System Diagram
The figure below shows a block diagram of the Sentinel / Sentry IIsc Fibre Optic Link system.
Transmitter
3dB
6dB
BP
LASER
POWER
CONTROL
9dB 12dB
SCM
CONTROL
CALIBRATE
SIGNAL
OPTICAL
FIBRE
LINK
CONTROL
DECODING
PSU
CONTROL
Receiver
¼dB ½dB
1dB
2dB
4dB
CONTROL &
MONITORING
PROCESSOR
SYSTEM CONTROLLER
The Sentinel / Sentry IIsc Fibre Optic Link uses Intensity Modulation (IM) for the transmission
of analogue data from the Transmitter to the Receiver. This scheme offers unparalleled levels
of bandwidth and dynamic range when compared to alternative modulation methods.
With Intensity Modulation, the intensity of the light source varies in direct proportion to the
magnitude of the modulating signal. The scheme has the following characteristics:
 The modulation bandwidth is the same as the bandwidth capability of the light source. In
alternative schemes such as Analogue to Digital conversion or Frequency Modulation, the
modulating bandwidth has to be significantly less than the bandwidth capabilities of the
light source. IM, therefore, offers the widest bandwidth.
 Light loss along the optical path (e.g. due to optical connector insertion loss) translates to
an attenuation of the transmitted signal. Therefore, if optical attenuation is not minimised
or compensated, then the gain of the link will be reduced.
 Dirt contamination or damage to the optical contacts may results in optical reflections back
into the transmitter laser diode that could degrade the noise performance of the system.
The laser diode is designed to minimise the effects of such reflections, but care should be
taken to protect and clean the optical contacts.
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Transmitter Module
Input Switch
The four way input switch allows the user to select one of four inputs at a time. Unused inputs
are grounded, and the circuit is designed to maximise the isolation between inputs.
High Impedance Buffer
The Sentinel IIsc FOL has been optimised for use as a wide bandwidth 50 system.
However it is necessary to present a high impedance to certain types of sensor. To facilitate
this, the user can switch a high impedance buffer into the signal path of the Transmitter
Module. This circuit is positioned before the 50 attenuators and pre-amplifier, and its use is
only valid when the system gain is set to 21dB (i.e. when all attenuators and the preamplifier are switched out of the signal path).
The impedance presented at the input is nominally 500k. The system bandwidth with the
High Impedance Buffer selected is reduced to 100MHz.
Pre-amplifier
A 12dB gain, low noise pre-amplifier may be switched into the signal path in order to improve
the noise figure of the overall system, and therefore monitor ultra low level signals. This preamplifier, in conjunction with the attenuators is controlled by the System Controller, and
allows the user to increase the gain from +21dB to +33dB in 3dB steps.
Attenuators
When the user selects the overall system gain (between -24dB to +33dB), the attenuators are
automatically selected or deselected to switch in and out of the signal path to achieve the
required gain. In this way, the system gain can be changed from +21dB (nominal system gain
with all attenuators switched out) to -24dB (maximum attenuation, with all attenuators
switched in).
Transmitter Test Signal
This circuit generates a high frequency squarewave (approx. 20MHz), which allows the user
to confirm the operation of the signal path without an input signal present. This is operated by
selecting "Test Signal" on the System Controller. The squarewave level is set so that the user
can monitor the level of the fundamental signal when observing the Receiver Unit output in
the frequency domain e.g. a spectrum analyser, or by measuring the peak-to-peak voltage
level in the time domain e.g. with an oscilloscope.
Transmit Amplifier
The Transmitter input signal is amplified by a broadband, high linearity, low noise amplifier to
a level suitable for modulating the laser diode.
Laser Bias and Matching
A broadband matching network maximises the coupling between the amplifier and the laser
diode. The light intensity output of the laser diode varies in direct proportion to the modulating
signal current generated by the transmit amplifier. A laser bias circuit biases the laser at the
optimum DC bias point for AC signal linearity, noise and bandwidth.
Control Decoding
This circuit decodes control signals received from the Receiver Unit. These control signals
are used to set the position of the signal switching relays, and to switch the various active
circuits on and off.
Power Supply Regulation and Control
A voltage supply and monitor circuit switches the Transmitter Module off if the supply voltage
falls below 12V. This prevents damage that can be caused to the Battery Pack if it is overdischarged. The supply voltage is regulated so that the system maintains full performance as
the battery voltage falls from above 15V to 12V.
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Battery Pack
There are two types of Battery Pack available: standard and high-capacity.
The Battery Packs can be maintained at full performance by the use of the appropriate PPM
battery charger Unit.
Typical operating times for a 2.0Ah capacity battery under normal operating conditions is 10
operational or 150 hours standby time. This can be scaled depending on the actual capacity
of the battery.
See battery handbook for further details.
Receiver Unit
Photodiode
The signal light from the Transmitter Module is converted back into an electrical signal by the
photodiode in the Receiver Unit. The light level is measured by the Receiver and reported on
the front panel.
AGC Amplifiers
The RF amplifier boosts the signal from the photodiode to generate the required system gain
at the output. A variable gain stage in the design allows for fine tuning of the receiver gain to
allow for variations in optical path loss.
The light level measured at the photodiode is monitored and the required adjustment to the
Receiver gain is calculated. The gain is corrected accordingly. This gain adjustment takes
place when the Transmitter Module is switched on, or when Receiver Calibration sequence is
selected.
Control & Communications
The Receiver Unit is controlled by an on-board processor that takes control signals from the
System Controller. Remote commands, ie. those which require control of the Transmitter
Module, are processed by the local Receiver Module. The Receiver then communicates
through the optical data link to the Transmitter Module.
Fibre Optic Cables
The optical signal path consists of singlemode fibre. This has been selected in preference to
multimode fibre as it offers far superior noise performance due to the absence of modal noise.
Modal noise is caused by the interference between the many modes present in multimode
fibre. High performance, low insertion loss optical connectors maintain optimum link
performance.
The low speed digital control signals from the Receiver Unit to the Transmitter Module are
sent over a multimode fibre.
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2 Installation
Safety Precautions
Refer to the Safety Information sheet at the beginning of this handbook for safety precautions
prior to operating mains powered equipment.
Initial Inspection
Unpack and inspect the equipment as soon as possible. If there is any sign of damage or any
parts missing, do not install the equipment before seeking advice from PPM or your local
agent.
The equipment received should correlate with the delivery documentation that is shipped with
the equipment. If there are any discrepancies, contact PPM or your local agent.
Receiver Module Installation
The Sentinel / Sentry IIsc Receiver Unit is fully compatible with the PPM System Controller
and Desktop Case and Subrack and can be installed in any available slot within the case.
Switch off the Controller before proceeding. Never remove or install modules with the power
connected.
Take care not to touch any electrical contact inside the System Rack Chassis as many
circuits within the system are sensitive to damage from Electro-Static Discharge.
To install the Sentinel / Sentry IIsc Receiver, first unscrew one blanking plate from the Case.
Check that the module guides are in place and gently slide in the Receiver, ensuring that it
does not foul the adjacent modules. The module should mate with the backplane connector
firmly to leave the front panel level with the other front panels.
Tighten up the two front panel screws firmly. Switch on the System Controller and select the
relevant module. Check that the Controller has correctly identified the module type.
The Receiver Unit is now installed.
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3 Setting up the Sentinel / Sentry IIsc FOLs
This section describes the connections between the Sentinel / Sentry IIsc FOL Transmitter
and Receiver units and the System Controller. It also describes how connections are made
between the Transmitter and Receiver units and external equipment.
Transmitter Connections
The figure below shows a front panel view of the transmitter module with battery pack.
OPTICAL
CONNECTOR
RF INPUTS
BATTERY
LINKING PLUG
Battery Pack Connection
The tab on the rear end of the Battery Pack should be located into the guide at the rear of the
Transmitter Module. The two bolt heads on the Battery Pack should be then lined up with the
guide holes on the Transmitter Module housing.
The Transmitter Module and the Battery Pack are linked by a shielded "U" link that pushes on
to the DC Output Connector and the Transmitter Module DC input connector. Once the
Battery Pack is located in position, the “U” Link can be pushed into position, and the outer
shells of the "U" link screwed finger tight onto the Transmitter Module and Battery Pack DC
connectors. Failure to tighten this connector may compromise the EMC shielding
performance of the Transmitter.
RF Signal Input
The input signals are fed in to inputs 1 to 4 on the Transmitter Module. Connection should be
made to the front panel with SMA male cables or adapters, and these should be tightened
with an SMA torque spanner of 0.8 to 1.1Nm. Do not under tighten as this may degrade
system performance. Do not overtighten as this will damage the equipment and cables.
Fibre Optic Cable Connection
Refer to page 3-3 for details of the connection of the Fibre Optic Cable connectors.
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Battery Pack Removal
To remove the Battery Pack from the Transmitter Module, the "U" Link for the DC Power
needs to be unscrewed and removed. The Battery Pack can then simply be lifted from the
side of the Transmitter Module so that it is clear of the two locating lugs and pulled out from
the locating slot at the rear of the Module.
CAUTION:
The Battery Pack is held in position by the “U” Link. Take care to support the Battery
Pack when removing this link so that the Battery Pack does not fall and cause injury or
damage.
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Lemo 3K Fibre Optic Connector
To maximise protection in adverse environments, the Sentinel / Sentry IIsc FOL has been
provided with rugged Lemo 3K type Fibre Optic Connectors.
These connectors feature a self-latching mechanism, which provides security against shock,
vibration and cable tension.
CAUTION
Although the Lemo 3K connector is a very reliable connector, it is an optical component, and
it relies on total cleanliness of the optical path for proper performance. Great care must be
taken to keep the white ferrules within the connector shell completely clean at all times.
Occasionally, it will be necessary to clean the optical contacts – refer to section 9 for details.
Connecting Lemo 3K Fibre Optic Connectors
Remove the protective dust cap from the cable mounted connector by holding the dust cap in
one hand, and pulling the connector out by its outer release sleeve with the other hand.
Remove the protective dust cap from the equipment by supporting the equipment with one
hand, and pulling the dust cap out with the other hand.
The 3K connectors are keyed and can only be inserted in one orientation. Correct alignment
is indicated by the alignment key-way and red alignment markings. The key/alignment mark
should be uppermost when the connector is being inserted.
The protective dust caps on the equipment and cable connectors should only be removed
immediately before the connectors are mated.
When the cable mounted 3K connector is inserted, it should be firmly pushed into the panel
mounted connector until the lugs are felt to latch into place.
Under no circumstances should the connector be forced into position.
Care should be taken not to drop the optical connector or to subject it to any other excessive
physical shock, particularly when it is not protected with the dust cap.
Disconnecting Fibre Optic Connectors
The connector is disengaged by a single straight axial pull on the slotted outer release sleeve.
This first disengages the latches and then withdraws the plug from the socket.
Immediately after removing the connectors, all protective dust caps should be fitted.
Care of fibre optic connectors
When the fibre optic cables are not connected, it is essential that the cable and equipment
connectors are protected by the dust caps provided with the system. Failure to do so may
result in damage to the fibre ends, which are critical to the system performance.
System performance may be compromised by dirt on the connector end or its alignment
surfaces. Refer to section 9 for instructions on cleaning the optical connectors.
Connector performance will be compromised if the end face is scratched.
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Receiver Connections
The figure below shows the connections on the Optical Receive Module front panel.
P
P
M
POWER LED
MODULE SELECTED
RF OUTPUT
RECEIVED OPTICAL
SIGNAL STRENGTH
SIGNAL
RLL
OPTICAL SIGNAL
OPTICAL
CONNECTOR
Sentry IIsc
Receiver
RF Signal Output
The output RF signal connector on the Receiver Unit is an SMA female type. Connection
should be made to the front panel with SMA male cables or adapters, and these should be
tightened with an SMA torque spanner of 0.8 to 1.1Nm. Do not under tighten as this may
degrade system performance. Do not overtighten as this will damage the equipment and
cables.
WARNING
As Sentinel & Sentry RX modules are AC coupled they will create a 1-2Vpeak DC transient
at start up into a 50 ohm load (approximately 5V into a 1Mohm load). The rise time is
~150uS and the FWHM time is ~400uS. Some very sensitive spectrum analyzers (such as
the R&S FSP40) have experienced front end failures, which are likely to be due to this initial
transient. Please make sure that the spectrum analyzer is EITHER tolerant to these DC
level OR is NOT connected to the RX output when the system controller is turned on.
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Fibre Optic Cable Connection
Refer to page 3-3 for details of the connection of the Fibre Optic Cable connectors.System
Interconnections
The figure below shows typical connections for a test system using the Sentinel IIsc FOL.
P
P
M
P
P
M
P
P
M
P
P
M
P
SIGNAL
SIGNAL
RLL
SIGNAL
RLL
P
M
SIGNAL
RLL
RLL
OPTICAL SIGNAL
OPTICAL SIGNAL
OPTICAL SIGNAL
OPTICAL SIGNAL
Sentry IIsc
Receiver
Sentry IIsc
Receiver
Sentry IIsc
Receiver
Sentry IIsc
Receiver
Once all the connections are made to the units, the System Controller can be switched on. All
functions of the Transmitter and Receiver are controlled through the System Controller unit.
Information on the status of the installed links is available on the status screens on the
System Controller.
All the controls available on the System Controller are also available via remote control from a
computer, or equipment controller attached to the System Controller via an RS232 or GPIB
link. This feature allows automated testing. More detailed information on remote control
operation is available in the Remote Control section of this handbook.
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4 Controlling the Sentinel / Sentry IIsc FOL
This section describes control of the Sentinel IIsc and Sentry IIsc fibre optic links through the
PPM System Controller and the corresponding remote control commands. Some knowledge
of the operation of the System Controller is required before this passage can be read.
Consult handbook Sxx-HB.
Using the System Controller to operate the Sentinel / Sentry
On power-up, the System Controller will always scan all modules in the System Case or
Subrack to determine the type of module fitted, and then select the first available controllable
module.
Module settings and status indication, communication protocols, remote powering etc. are all
selected from a menu driven graphical user interface on the front panel of the System
Controller. The controller uses a large matrix display and softkeys to interface with the user.
The functions of the softkeys change depending on the current displayed screen and a
functional description appears on the LCD adjacent to each key. Where there is no legend
next to a key, that key is not implemented.
The menu structure for controlling the Sentinel and Sentry IIsc modules comprises three main
areas, all accessed from the horizontal buttons beneath the LCD screen. These are Modules
Settings, Module Status and Global Settings.
The setup of the Controller itself, which includes remote control and display settings, is
accessed through the System Settings button to the right of the LCD display. Details of this
can be found in the System handbook, Sxx-HB. This can be obtained from your local PPM
representative, or downloaded from the PPM website.
Screen Title
Description
Module Settings
Edit all parameters for a particular FOL (Transmitter and Receiver)
Module Status
Poll a specific module pair for information
Global Settings
Control non-input-specific parameters of FOL
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Switching on the Sentry / Sentinel IIsc FOL
Power the case/rack using the red mains power switch on the rear panel. The System
Controller's power button glows when in the standby state.
To power the controller, press the power button located to the top right of the LCD screen.
The power button glows when the unit is in standby mode. After a brief start up screen you
will be presented with the “Module Settings” screen. A graphical representation of the front of
the SCT-1 is shown below:
Selecting a module
To select the module you wish to control, press the button adjacent to the “Select Module”
icon. The selected module is displayed on the screen as shown below:
The selected LED on the corresponding receiver should also be green.
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Transmitter on
To switch on a Transmitter Module, move the cursor down to the transmitter selection by
pressing the button adjacent to the “down arrow” icon. The transmitter section of the display
should now be highlighted as below:
Rotate the function wheel clockwise until Transmitter status is displayed as “on”, the signal
relays within the Transmitter Module will be heard to operate for a few seconds, and then the
RLL bar LED array on the Receiver Unit front panel will indicate the optical level at the
Receiver. If all LEDs are lit, the signal strength is within the AGC range of the receiver. For
optical input powers beneath this level, each LED that is extinguished indicates another 1dB
of optical insertion loss that should be calibrated out manually.
If the message “NO CARRIER DETECTED” is displayed on the LCD, refer to the fault finding
guide in section 6.
Input Channel Select
The System Controller automatically selects Input 1 when it is switched on. The currently
selected input is indicated by the “Active input” display, shown below:
The other inputs may be selected by pressing the buttons below the icons numbered 1 to 4
on the system controller display.
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Setting the Link Gain
The gain of the Sentry / Sentinel IIsc FOL is nominally -24dB. With the gain set to this level,
the switchable pre-amplifier is deselected and all attenuators within the SCM are switched
into the signal path. The gain may be varied by the user from -24dB to +33dB in order to
match the wide dynamic range of the Sentinel / Sentry IIsc FOL to the level of the signal to be
monitored.
On the “Modules Settings” screen, select the input required, and then highlight the “Gain”
section of the display as shown below:
This can be achieved by, either stepping through the selections using the down arrow, or
using the gain shortcut button, this is below the “Gain” icon.
To change the gain value, use the function wheel. The gain of the transmitter will only change
after the function wheel has been stationary for 2 -3 seconds.
The gain is adjustable in 3dB steps.
Changing the Input Impedance
It is possible to change the input impedance of the Sentry / Sentinel IIsc Transmitter from 50
to a high impedance of 500k (nominal). Selection of the high impedance input limits the
system bandwidth to 100MHz.
To change the impedance of an input, select the input you wish to change, highlight the
Impedance section of the display by stepping through the selections using the down arrow.
Screen shot shown below:
Rotate the function wheel to change the impedance. The Sentinel IIsc FOL has been
optimised for ultra-wide bandwidth and wide dynamic range. As a result, the attenuators and
other wideband circuits are all 50, and the High Impedance buffer circuit is placed before
these circuits in the Transmitter. The gain of the system should be set to 21dB when the
High Impedance mode selected, as operation at other system gains is likely to compromise
the noise and linearity performance of the system.
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Transmitter Test Signal
The 20MHz (nom.) squarewave test signal generator in the Transmitter Module can be
switched in to verify the link gain. This is done by monitoring the signal at the Receiver output
on a high frequency oscilloscope. The expected Receiver output level is 250mVp-p +/-25mV
when the system gain setting is set to +21dB.
To enable the test signal, highlight the test signal section of the display by stepping through
the selections by using down arrow, as shown below:
Rotate the function wheel to enable/disable the test signal.
Max Input Displayed Unit Select
The maximum allowable input is displayed on the screen, as shown below:
The maximum allowable input that may be applied can be toggled between dBm, dBV and
mV.
To change the units, select the button adjacent to the system menu icon, and then select the
button adjacent to the Global Menu icon.
On the Global Settings screen, change the units using the function wheel, and then press the
button adjacent to the confirm icon when you are happy with your selection. To return to the
Module Settings screen, press the button adjacent to the control modules icon.
The Max Input value is automatically changed as the system gain is changed.
4-5
PPM LTD 2015
Operating the Sentinel IIsc Receiver Calibration Function
The Sentinel / Sentry IIsc modules automatically calibrate the link when "Transmitter On" is
selected. If re-calibration is required, this function should be selected at the System
Controller from Module Status menu.
The Receiver Calibration function performs the following operations :
The Receiver measures the received optical power level. This value is used to set the RF
gain of the Receiver in 0.25dB steps so that the overall system gain is within 0.25dB of the
indicated gain on the Controller screen.
This allows small variations in optical path loss to be accommodated, minimising the impact of
variations in optical connector insertion losses. This technique maximises the dynamic range
of the link, although it may result in small gain variations of no more than 0.25dB every time
the Calibrate function is selected. In certain situations, this should be considered (e.g. if the
link gain is accurately calibrated with a network analyser for a precise measurement). In such
a situation, the Calibrate function should not be initiated between the network analyser
calibration and the measurement.
If the receiver optical power is lower than can be accommodated by the AGC calibration
circuit, the receiver gain is set to its maximum value to compensate in part for the loss. The
actual insertion loss can be monitored either directly from the Receiver front panel LEDs, or
by accessing the RLL function on the Module Status Screen of the Controller for the module
in question.
To enter the module status screen from the module setting screen, first select the button
adjacent to System Menu icon and then select the button adjacent to the Module Status icon.
To return to the Module Settings display select the button adjacent to the Control Modules
icon.
RLL BAR LED
STATUS
MEANING OF INDICATION
SYSTEM GAIN

OPTICAL PATH LOSS < 4dB
Gain accurate

4dB < OPTICAL PATH LOSS < 5dB
!! Gain setting in error !!

5dB < OPTICAL PATH LOSS < 6dB
!! Gain setting in error !!

6dB < OPTICAL PATH LOSS < 7dB
!! Gain setting in error !!

7dB < OPTICAL PATH LOSS < 8dB
!! Gain setting in error !!

8dB < OPTICAL PATH LOSS < 9dB
!! Gain setting in error !!

9dB < OPTICAL PATH LOSS < 10dB
!! Gain setting in error !!

OPTICAL CARRIER LOST
-
4-6
PPM LTD 2015
5 Remote Commands
All the functions for the SCT-1 can be controlled remotely with a computer via an RS232 link or a GPIB link. For information about setting up a connection, or
remote control of the controller's system settings, please consult the System, Sxx-HB.
Please note: As standard, All GPIB commands written to the system controller generate a response, it is important to read these responses
back from the controller even if the data is not required. Failure to do so will cause the system controller not accept another command for 2 – 3
seconds.
To disable the “Ok” responses please see “REMOTE OFF” command.
All commands refer to the currently selected module unless otherwise specified. "" represents a SPACE character. All responses are followed by [CR] and
[LF].
Command
Description
Responses
Meaning
*IDN?
System Data, Identification query
PPM,SCT-1,FOL,V1.3
Folnet successfully found at queried GPIB
address.
TXON
Turn Transmitter ON
CARRIER DETECTED
Ok
Ok
NO CARRIER DETECTED
Ok
No Optical Carrier at Receiver
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
TXOFF
INP1
INP2
INP3
Turn Transmitter OFF
Select Input 1
Select Input 2
Select Input 3
5-7
PPM LTD 2015
Command
Description
Responses
Meaning
INP4
GAIN-x
Select Input 4
Set Gain of Current Input Channel to -xdB
Ok
Ok
Ok
Ok
NOT AVAILABLE
Ok
Gain setting out of range
Ok
Ok
NOT AVAILABLE
Ok
Ok
Ok
Ok
Gain setting out of range
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
See Below
See SYS Below
See SYS Below
Ok
Ok
Ok
See SYS Below
See SYS Below
See SYS Below
See SYS Below
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
GAIN0
GAIN+x
Set Gain of Current Input Channel to 0dB
Set Gain of Current Input Channel to +xdB
IMP50
Select 50 Input Impedance for Current Input
Channel
Select High Input Impedance for Current
Input Channel
Turn Tx Test Signal ON for Current Input
Channel
Turn Tx Test Signal OFF for Current Input
Channel
Puts Maximum Input Display in dBm
Puts Maximum Input Display in dBV
Puts Maximum Input Display in Volts Peak-toPeak
Report Status of Current Module
Operates the same as SYS command
Returns only SYS Header Section
IMPHIZ
CALON
CALOFF
DBM
DBUV
VPP
SYS
REPORTALL
REPORTMO
D
REPORTINP1
REPORTINP2
REPORTINP3
REPORTINP4
ALLCALON
ALLCALOFF
ALLTXON
Returns only Input 1 information
Returns only Input 2 information
Returns only Input 3 information
Returns only Input 4 information
Turn Tx Test Signal On, All Channels
Turn Tx Test Signal Off, All Channels
Turn all Transmitters On
5-8
Ok
PPM LTD 2015
Command
Description
Responses
Meaning
ALLTXOFF
MOD1
Turns all Transmitters Off
Select Module 1
Ok
Ok
No Module Present
MOD2
Select Module 2
MOD3
Select Module 3
MOD4
Select Module 4
MOD5
Select Module 5
MOD6
Select Module 6
MOD7
Select Module 7
MOD8
Select Module 8
LOCAL
REMOTE
Puts SCT in Local mode
Puts SCT in Remote mode
REMOTEOFF
Puts SCT in Remote mode, but also removes
the “OK” response after completion of every
command sent.
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
MODULE DISABLED
Ok
Ok
Ok
NOT AVAILABLE
Ok
NONE
5-9
Ok
No Module Present
Ok
No Module Present
Ok
No Module Present
Ok
No Module Present
Ok
No Module Present
Ok
No Module Present
Ok
No Module Present
Ok
Ok
Module is already in remote mode
PPM LTD 2015
Command
Description
Responses
Meaning
STAT
Queries the status of each module position.
0,0,0,0,0,0,7,6
Ok
Returns 8 numbers where each number
represents the type of module installed in
each of the 8 possible positions:
0=none
6=Sentinel
7=Sentry
REMOTEON
Puts SCT in Remote mode, but also adds the
“OK” response on completion of every
command. This command is only required if
responses have been previous removed by a
REMOTE OFF command.
Ok
Ok
SET?x
Queries module x
1,1,Y,-24,50,2,N,-24,50,3,N,-24,50,4,N,24,50
Ok
The output is formatted as
“A,B,C,D,E,B,C,D,E,B,C,D,E,B,C,D,E”
Where the character represented by “A” is
the module queried.
The character represented by “B” is the
module input.
The character represented by “C” is Y if
the input is selected or N if the input is not
selected.
The character represented by “D” is the
gain.
The character represented by “E” is the
input impedance, 50 for 50 ohm and HIZ
for high impedance.
MODULE DISABLED
Ok
5-10
No Module Present
PPM LTD 2015
Command
Description
Responses
Meaning
SETa,b,c,d
Set a modules input, gain and impedance in
one command
Ok
MODULE DISABLED
Ok
Ok
No Module Present
a=module
b=input
c=gain
d=impedance
Examples:
SET 1,1,-3,HIZ
Set module 1, input 1 to -3dB of gain and
High impedance.
SET 1,3,33,50
Set module 1, input 3 to 33dB of gain and
50ohm impedance.
5-11
PPM LTD 2015
Command
Description
Responses
Meaning
GPIB x
This sets the GPIB response timeout. x is
between 0 and 15.
Ok
Ok
0= OFF
1= 16us
2= 32us
3= 128us
4= 256us
5= 1ms
6= 4ms
7= 16ms
8= 33ms
9= 131ms
10= 262ms
11= 1s
12= 4s
13= 17s
14= 34s
15= 134s
Note: this command may cause unexpected results if
the GPIB timeout is either set too low or too high and
therefore should be used with care.
Other responses
SCT1 IS IN LOCAL MODE
Ok
UNSUPPORTED FUNCTION
Ok
SCT is in Local Mode - send
REMOTE command or press "Go
Remote".
Function is not supported by the type
of module selected.
5-12
PPM LTD 2015
SYS (or REPORT ALL) Command Response
MODULE SELECTED: 1 SENTRY 2SC
TRANSMITTER STATUS : **********
BATTERY STATUS : NOT TESTED
CARRIER
: Off
TRANSMITTER
: Off
CALIBRATE
: Off
INPUT : 4



 REPORT MOD



INPUT : 1 ********
GAIN
: -24.0 dB
MAX INPUT : 14.1V mV p-p
INTEGRATOR : OFF
IMPEDANCE : 50 Ohm
FILTER
: OFF
INPUT : 2 ********
GAIN
: -24.0 dB
MAX INPUT : 14.1V mV p-p
INTEGRATOR : OFF
IMPEDANCE : 50 Ohm
FILTER
: OFF
INPUT : 3 ********
GAIN
: -24.0 dB
MAX INPUT : 14.1V mV p-p
INTEGRATOR : OFF
IMPEDANCE : 50 Ohm
FILTER
: OFF
INPUT : 4 ********
GAIN
: 0.0 dB
MAX INPUT : 894.0 mV p-p
INTEGRATOR : OFF
IMPEDANCE : 50 Ohm
FILTER
: OFF
OK


 REPORT INP1



It should be noted that the INTEGRATOR and FILTER functions are redundant and only appear in the SYS response data to maintain compatibility with the
FOLNET controller.
5-13
PPM LTD 2015
Please note: The following commands return multiple lines, and therefore a suitable program in LabVIEW or equivalent will have
to be written to receive the data from these commands when using GPIB.
"" represents a SPACE character
Command
Meaning
Number of lines returned
(in REMOTE ON mode)
SYS
REPORTALL
REPORTMOD
REPORTINP1
REPORTINP2
REPORTINP3
REPORTINP4
Report Status of Current Module
Report Status of Current Module
Returns only SYS Header Section
Returns only Input 1 information
Returns only Input 2 information
Returns only Input 3 information
Returns only Input 4 information
33
33
9
7
7
7
7
5-14
PPM LTD 2015
6 Maintenance and Fault-Finding Guide
Refer to the following table that gives a list of commonly encountered problems and
suggested solutions.
Fault
Possible Causes
Solution
Module Not Recognised by
System Controller
Module Not Installed
Correctly or not responding
to Commands from
Controller.
Switch off Controller, remove
Module and re-install
following instructions on page
2-1
Correct Controller Software
not Installed
Update Controller Software
from http://www.ppm.co.uk
Discharged Battery Pack
Recharge/replace Battery
Pack
System Controller indicates
"Carrier Not Detected"
Fibre Optic Cable has not
been connected correctly
Dirt on the fibre optic
connectors
Signal or Control fibre has
been broken
Check fibre optic connectors
are fitted correctly
Clean the fibre optic
connector with the correct
fibre optic cleaning kit. Refer
to Section 9.
Contact PPM
Gain or Test Signal incorrect
The gain of the system
appears to be incorrect
Operate the Receiver
Calibration function, which
will reset the optical gain of
the system.
Receiver Calibration does not
resolve gain inaccuracy
Connectors are dirty or
damaged
Clean the fibre optic
connector with the correct
fibre optic cleaning kit. Refer
to section 9. If this does not
remedy the problem, contact
PPM.
Unit appears to respond
slowly to GPIB commands
All GPIB commands written
to the system controller
generate a response, these
must be read back from the
controller even if the data is
not required
Always do a GPIB read after
a GPIB write to the system
controller
In the event of any problems with the equipment contact PPM or your local agent.
6-1
PPM LTD 2015
7 System Specifications
The following specifications show the performance of Test & Measurement Fibre Optic Links.
LINK PERFORMANCE
Number of Input Channels
Input/Output Impedance
Frequency Response (-3dB)
Risetime
Output P1dB / IP3
Dynamic Range
Noise Figure
(100MHz / 21dB Gain)
(100MHz / 33dB Gain)
Gain Adjustment
Gain Tolerance (+21dB gain)
Signal Inversion
Flatness (+21dB gain)
VSWR
Optical Self-Calibration Range
Built-In Transmitter Test Signal
Frequency
Amplitude
SENTRY IISC
SENTINEL IISC
4 switchable inputs
-Z Buffer*
<40Hz to >500MHz
<2kHz to >1GHz
< 1.4ns
< 450ps
+5dBm / +11dBm
139dB in 1Hz bandwidth
17dB
11.0dB
-24dB to +33dB in 3dB steps
±1dB
Non-inverting
Inverting
±1.2dB, 60Hz to 400MHz ±1.2dB, 3kHz to 800MHz
<2:1
7.5dB electrical, 0.25dB steps
20MHz squarewave (nominal)
250mVp-p ± 10%
ENVIRONMENT
Operating Temperature
Plug-In Receiver
Shielded Transmitter
Storage Temperature
FIBRE OPTIC SPECIFICATION
Optical Connections
Output Power
Cross-Site Cable Lengths
+10C to +40C
0C to +40C
-40C to +70C
LEMO 3K dual ferrule connector
+4.5dBm nominal (IEC825 Class 1 Laser Radiation
Hazard)
50m, 100m, 200m
PHYSICAL FORMAT
Transmitter Module
Housing
Weight
Receiver Module
Housing
Weight
7hp Plug-In compatible with SRK-3 Desktop Case
600g
POWER SUPPLY
Transmitter Module
Receiver Module
Shielded Battery Pack, Standard or High capacity
Power derived from subrack/case
Shielded Module
1.5kg not including battery pack
RF CONNECTION
Transmitter Input Connectors
Receiver Output Connector
FRONT PANEL INDICATION
Receiver
Controller SCT-1
Gold Plated SMA (4off)
Gold Plated SMA (1off)
Module Selected LED, Received Light Level Display
Full System Status available via Colour LCD
Application Notes
Please contact PPM Ltd or your local agent for Application Notes describing the potential
applications for the Sentinel / Sentry IIsc FOL.
7-1
PPM LTD 2015
8 Product Warranty
The Company guarantees its products, and will maintain them for a period of one year from
the date of shipment and at no cost to the customer. Extended warranty options are available
at the time of purchase.
Please note that the customer is responsible for shipping costs to return the unit to PPM.
The Company or its agents will maintain its products in full working order and make all
necessary adjustments and parts replacements during the Company’s normal working hours
provided that the Customer will pay at the rates currently charged by the Company for any
replacements made necessary by accident, misuse, neglect, wilful act or default or any cause
other than normal use.
Claims must be made promptly, and during the guarantee period.
IMPORTANT:Please contact both your selling agent and PPM prior to returning any goods for
Warranty or Non-Warranty repairs. Goods will not be accepted without a valid Goods
Return Number (GRN).
8-1
PPM LTD 2015
9 Fibre Optic Connector Cleaning Procedure
Although the Lemo 3K connector is a very rugged and reliable connector, it will occasionally
become necessary to clean the optical contacts in accordance with the following procedure.
PPM provide a Lemo 3K Cleaning Kit which contains the following items:

Extraction Tool for Fibre Optic Contact

Cotton buds for cleaning optical contacts.
The user should source the following items locally:

Reagent grade Iso Propyl Alcohol (IPA). NB IPA is flammable, and appropriate attention
should be paid to relevant local and national safety regulations and guidelines.

Pressurised clean air supply e.g. compressed air aerosol (“air duster”)
A Lemo 3K mating pair consists of an optical plug (usually cable mounted), and an optical
socket (usually equipment panel mounted).
CAUTION
Throughout the process, great care must be taken not to use materials that may scratch the
optical contacts. Even microscopic scratches may severely degrade the performance of the
connector.
Cleaning the Optical Plug
Dampen the cotton bud with IPA, and gently wipe over the white ceramic optical contact
visible inside the plug. Remove excess IPA from the contact with the compressed air.
It may be possible to clean the contact adequately without the use of IPA or compressed air
simply by wiping the contact with a dry cotton bud.
Cleaning the Optical Socket
The optical socket is simply an optical plug with an alignment ferrule. This ferrule must be
withdrawn to give access to the optical contact.
Screw the threaded end of the extraction tool into the socket until it comes to a stop. Now
gently and firmly pull back on the extraction tool to remove the alignment ferrule.
Use a cotton bud and IPA as before the clean the exposed contact inside the connector.
To replace the alignment ferrule, simply push it back into place with the extraction tool, and
then unscrew the extraction tool.
It may be possible to clean the contact adequately without the use of IPA or compressed air
simply by wiping the contact with a dry cotton bud.
9-1
10 Spares Information
The following spares are available with the Sentinel IIsc system:
PPM Part Number
Description
73553
Lemo 3K Fibre Optic Connector Cleaning Kit
CAUTION Hazardous voltages exist within the PPM T&I System Desktop Cases and
Subracks. Adjustment, maintenance and repair of the equipment should only be
carried out by suitably qualified personnel.
TRx-HB-6 Sentinel / Sentry IIsc Test & Measurement Fibre-Optic-Link System
CR3359
 PPM LTD., 2015.
NO PART OF THIS DOCUMENT MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT PRIOR WRITTEN PERMISSION.
PPM LTD., 65 SHRIVENHAM HUNDRED BUSINESS PARK, SWINDON, SN6 8TY, UK.
TEL: +44 1793 784389 FAX: +44 1793 784391
EMAIL : info@ppm.co.uk WEB: www.ppm.co.uk
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