TECSYSTEM FO 935 User manual

1MN0224 REV.0
operates with ISO9001 certified quality system
http://www.tecsystem.it
R. 1.1 12/01/22
“Translations of the original instructions”
ENGLISH
TECSYSTEM S.r.l.
20094 Corsico (MI)
Tel.:[phone]
Fax:[phone]
FO 935
INSTRUCTION MANUAL

2
FO 935
PAGE
1) SAFETY REQUIREMENTS
……….......................................
4
2) ACCESSORIES
…………………………………..
5
3) TECHNICAL SPECIFICATIONS
…………………………………..
6
•FO 935 BASIC/D
…………………………………..
—
•CONC.CFO 521
………………………………….
8
•FO TEMPERATURE SENSORS
…………………………………..
—
4) FO 935 FRONT PANEL
…………………………………..
9
•DISPLAY
…………………………………..
10
•OPERATING PROGRAM CONTROL
………………………………….
—
•NOTES ON SCAN AND MAN FUNCTIONS
…………………………………..
—
•LED TEST
…………………………………..
—
•ALARM RELAY TEST
…………………………………..
—
•ALARM RELAY SILENCING
…………………………………..
—
5) CFO 521 / FO SENSORS
…………………………………..
11
•CFO 521 DIMENSIONS / INSTALLATION
…………………………………..
—
•FO SENSORS DIMENSIONS / INSTALLATION
…………………………………..
12
•CONNECTIONS OF THE CONC.CFO 521
…………………………………..
—
•CFO 521 CONCENTRATOR OPERATION
…………………………………..
13
6) FO 935 ASSEMBLY
…………………………………..
14
7) ELECTRICAL CONNECTIONS
…………………………………..
15
•FO 935 BASIC BACK
…………………………………..
—
•FO 935 D BACK
…………………………………..
—
•POWER SUPPLY
…………………………………..
16
•ALARMS AND VENTILATION
…………………………………..
17
•FAULT AND RESET MESSAGE SEQUENCE
…………………………………..
—
•SENSOR DIAGNOSTICS CONC. CFO 521
…………………………………..
—
•PROGRAMMED DATA DIAGNOSTICS
…………………………………..
18
•TEMPERATURE DIAGNOSTICS
…………………………………..
—
INTRODUCTION
First of all we wish to thank you for choosing to use a TECSYSTEM product and recommend you read this instruction
manual carefully: You will understand the use of the equipment and therefore be able to take advantage of all its
functions.
ATTENTION! THIS MANUAL IS ONLY VALID FOR THE VERSION FO 935 BASIC AND FO
935 D.
TABLE OF CONTENTS

3
FO 935
PAGE
•COOLING FAN CONTROL
…………………………………..
—
•FAN TEST
…………………………………..
—
8) PROGRAMMING
…………………………………..
19
•FO 935 BASIC/D PROGRAMMING
…………………………………..
—
•PROGRAMMING NOTES
…………………………………..
21
9) FAIL SAFE FUNCTION
…………………………………..
—
10) RS485 MODBUS (only for FO 935 D)
…………………………………..
22
•INTRODUCTION TO THE MODBUS INSIDE MODULE
…………………………………..
—
•OPERATING NOTES
…………………………………..
—
•DATA TRANSMISSION ON MODBUS NETWORK
…………………………………..
—
•RS485 ELECTRICAL CONNECTIONS
…………………………………..
—
•DATA FRAME
…………………………………..
—
•DATA PACKET
…………………………………..
—
•FUNCTION CODE
…………………………………..
23
•CODE 3(10).
…………………………………..
—
•CODE 16(10).
…………………………………..
—
•NOTES FOR REMOTE PROGRAMMING
…………………………………..
—
•ERROR CODES
…………………………………..
24
•UNACCEPTABLE DATA
…………………………………..
—
•ILLEGAL DATA
…………………………………..
—
•INTERROGATION FREQUENCY
…………………………………..
—
•MODBUS MAPPING TABLE
…………………………………..
25
11) WARRANTY REGULATIONS
…………………………………..
30
12) TROUBLESHOOTING
…………………………………..
—
13) EQUIPMENT DISPOSAL
…………………………………..
—
14) USEFUL CONTACTS
…………………………………..
31

4
FO 935
SAFETY REGULATIONS
ATTENTION:
Read the manual carefully before starting to use the control unit. Keep the instructions for future reference.
Do not open the device. Touching any internal components can cause electric shock. Contact with a voltage
over 50 Volts can be fatal. To reduce the risk of electric shock, do not dismantle the back of the device for any
reason. Moreover its opening would void the warranty.
Before connecting the device to the power supply, make sure that all the connections are correct.
Always disconnect the unit from the supply before any cabling modification.
Any work on the equipment must be entrusted to a qualified engineer.
Failure to comply with these instructions can cause damage, fires or electric shock, and possible serious
injuries!
POWER SUPPLY
The FO 935 control unit can be supplied by 85 to 260 Vdc-Vac, irrespectively of polarity in Vdc. Before using it, make
sure the power cable is not damaged, knotted or pinched. Do not tamper with the power cable. Never disconnect the
unit by pulling the cable and avoid touching the pins. Do not carry out any operations of connecting/disconnecting with
wet hands. To disconnect the device, do not use objects such as levers. Immediately disconnect the device if you smell
burning or see any smoke: contact assistance.
LIQUIDS
Do not expose the equipment to splashes or drops, do not position it in places with humidity exceeding 90% and never
touch with wet or damp hands. If any liquid penetrates the control unit, disconnect it immediately and contact technical
assistance.
CLEANING
Disconnect the power cable before cleaning the control unit, use a dry cloth to dust it, without any solvent or detergents,
and compressed air.
OBJECTS
Never insert any objects into the cracks of the control unit. If this happens, disconnect the control unit and contact an
engineer.
USE RESERVED TO QUALIFIED PERSONNEL
The purchased goods are a sophisticated electronic device that is completely unsuitable to be used by non-qualified
personnel. Any work must be carried out by a specialist engineer.
ACCESSORIES
The use of non-original accessories or spare parts can damage the unit and endanger users' safety. In the event of
faults, contact technical service.
LOCATION
Install the control unit indoors, in a place protected from water splashes and from the sun’s rays. Do not place near heat
sources exceeding the parameters stated in this manual. Position on a stable surface, far away from any possible
vibrations. Position the unit as far away as possible from any intense magnetic fields.
REPAIRS
Do not open the control unit. For any fault, always use qualified personnel. The opening of the control unit and/or the
removal of the series identifying label entails the automatic forfeiture of the warranty. The Warranty seal is applied to all
devices, any attempt to open the unit would break the seal and cause the consequent automatic forfeiture of the
warranty.
TECHNICAL INFORMATION OR REPORTING INFORMATION
Mail: [e-mail] —tel.:[phone]

5
FO 935
The FO system boxes contain the following objects:
FO 935 control unit
FO 935 control unit
Start guide and QR code
2 blocks for panel fixing
1 Terminal 3 pitch poles 5 supply
Code:2PL0367 - Screw tightening torque 0.5Nm
1 terminal 12 pitch poles 5 relays
Code:2PL0361 - Screw tightening torque 0.5Nm
1 Terminal 4 pitch poles 3.81 connection CFO 521
Code:2PL0368 - Screws tightening torque 0.25Nm
1 Terminal 3 pitch poles 3.81 RS485 (*)
Code:2PL0366 Screws tightening torque 0.25Nm
(*) Only for version D
CFO 521 Concentrator
CFO 521 Concentrator
Start guide and QR code
2 Terminals 4 pitch poles 3.81 connection FO 935 and CFO 521
Code:2PL0368 - Screws tightening torque 0.25Nm
1 Terminal 3 poles pitch 3.81 Pt100 CH4
Code:2PL0366 - Screws tightening torque 0.25Nm
ACCESSORIES
ATTENTION: always install the device using the terminals included in the pack.
The use of terminals other than those included with the control unit could cause malfunctions.

6
FO 935
TECHNICAL SPECIFICATIONS
FO 935 BASIC
FO 935 D
POWER SUPPLY
Supply rated values
85-260 Vda-Vac
50/60HZ
85-260 Vda-Vac
50/60HZ
Vdc with invertible polarities
●
●
INPUTS
1 digital input (FO IN) connection CONC.CFO 521
●
●
Connections on removable terminal boards
●
●
OUTPUTS
2 alarm relays (ALARM AND TRIP) SPDT
●
●
1 relay for faulty probes or operating anomaly (FAULT) SPST
●
●
2 ventilation management relays SPST FAN1 and FAN2
●
●
Output relays with 10A-250Vca-res COSФ=1 contacts
●
●
RS485 Modbus RTU output
NO
●
DIMENSIONS
100x100 mm–din43700-prof .131mm (including terminal block)
Hole 92 x 92 mm
Hole 92 x 92 mm
FO SENSORS
3 temperature sensors in fibre optic 2.5mt
Start guide and QR code

7
FO 935
TECHNICAL SPECIFICATIONS
FO 935 BASIC
FO 935 D
TESTS AND PERFORMANCE
●
●
Construction in compliance with the EC regulations
●
●
Protection from electrical interferences EN 61000-4-4
●
●
Dielectric strength 1500 VAC for 1 min. between output relay and FO
IN input, relay and power supply, and FO IN input and power supply
●
●
Reading range: -35°C to +195°C
●
●
Interface precision1% vfs, ±1 digit
●
●
Ambient operating temperature from –20°C to +60°C
●
●
Permitted humidity 90% without condensate
●
●
Polycarbonate frontal film IP65
●
●
Container NORYL 94 _V0
●
●
Absorption 7.5VA
●
●
Self-diagnostic circuit
●
●
Electronic part protective treatment
Optional
Optional
DISPLAY AND DATA MANAGEMENT
2 x 13 mm displays with 3 digits to display temperatures, messages
and channels
●
●
3 LEDs to display the state of the alarms of the selected channel
(ALARM-TRIP-FAULT)
●
●
4 LEDS selection of display mode (SCAN-AUTO-MAN-T.MAX)
●
●
2 LEDs to display the state of FAN1 and FAN2
●
●
Temperature control from 1°C to 190°C (alarms)
●
●
2 alarm thresholds for channels 1-2-3
●
●
2 alarm channels for channel 4
●
●
2 ON-OFF thresholds FAN 1 and FAN 2 ventilation
●
●
FO sensor diagnostics (FCC-FOC-FLT)
●
●
Data memory diagnostics (Ech)
●
●
Communication diagnostics FO 935 to CFO 521 (TEC)
●
●
Access to programming through front keyboard
●
●
Automatic exit from programming, display and relay test after 1
minute of inactivity
●
●
Incorrect programming warning
●
●
Selection between channels automatic scanning, hottest channel or
manual scanning (SCAN-AUTO-MAN)
●
●
Storage of maximum temperatures reached by channels and alarm
status (TMAX)
●
●
Front key to reset the alarms
●
●

8
FO 935
TECHNICAL SPECIFICATIONS
CONC. CFO 521
INPUTS
1 FO 935 digital BUS input
FO IN
3 fibre optic FO sensor inputs (ST connectors)
CH1-CH2-CH3
1 2/3-wire Pt100 probe input
CH4
OUTPUTS
1 digital BUS output
FO OUT
TESTS AND PERFORMANCE
3 signalling LEDs L1-L2-L3
●
Work environment temperature
From -25°C to +60°C
Permitted humidity 90% without condensate
●
Degree of protection IP00
●
PC UL 94 HB container
●
Electronic part protective treatment
Optional
DIMENSIONS
145x106.7x55mm
●
Concentrator fixing bracket CONC. CFO 521
Included
TECHNICAL SPECIFICATIONS
TEMPERATURE SENSOR
FO (FIBRE OPTIC)
TESTS AND PERFORMANCE
Reading range
-35°C to +195°C
Interface precision
±1.0°C
Permitted humidity 90% without condensate
●
External protection
FEP
DIMENSIONS
Length
2.5mt
Tip probe diameter
2.3mm
Fibre connector model
ST

9
FO 935
1)
3-digit temperature display
12)
Enter/Reset button
2)
Control unit series
13)
Programming/Setting key
3)
TRIP signalling (red) LED
14)
Led/relay test key
4)
ALARM signalling (yellow) LED
15)
Modbus communication RS (green) LED
(ONLY FO 935 D)
5)
FAULT signalling (red) LED
16)
3-digit channel display
6)
FAN 1 (yellow) LED
17)
T-max mode selection (red) LED
7)
FAN 2 (yellow) LED
18)
Man mode selection (yellow) LED
8)
Display mode selection key
19)
Auto mode selection (green) LED
9)
Fixing blocks
20)
Scan mode selection (yellow) LED
10)
UP key
21)
Fixing blocks
11)
DOWN key
FRONT PANEL
1
2
3
4
5
6
7
8
9
10
11
12
14
13
15
16
17
18
19
20
1MN0224 REV.0
21

10
FO 935
DISPLAY
The first display is dedicated to temperatures.
The second display to the monitored channel.
When the device is switched on or after a reset, the model of the control unit, the type of sensors, VER "00" (firmware
version) and the temperature range of the device and the identification abbreviation are always shown on the display.
Pressing the MODE key, the display modes can be set:
•SCAN: the control unit shows in scanning (every 2 seconds) all the enabled (°C) and disabled (NO) channels.
•AUTO: the control unit displays the hottest channel automatically.
•MAN:manual reading of the channel temperature using the up/down keys
•T.MAX: the display shows the maximum temperature of the channel selected with the cursor keys.
In the event of a fault, the Tmax value is replaced with the type of fault stored (fcc-foc).
Turning on the Trip Alarm-Fault LED warns of any events that have occurred.
The recordings are always successive to the moment in which the T.Max is reset (by pressing RESET).
OPERATING PROGRAM CONTROL
To control the protection levels programmed, press the PRG key twice to access the VIS programme. Repeatedly pressing
the PRG key, you can scroll through all the previously loaded values in sequence. After 1 minute's keyboard inactivity, the
programming display procedure is automatically abandoned.
To stop the display, press the ENT key.
NOTES ON SCAN AND MAN FUNCTIONS
During the SCAN and MAN modes, the operation of the FO 935 can be displayed.
1) RUN cPU:
This message appears upon ignition of the device.
2) Ech Err:
This message appears when damage in the EEPROM memory is detected.
Pressing Reset will cancel the message and restore the original default parameters, listed in the programming paragraph
on pages 19-20 return the control unit to TECSYSTEM for repairs.
3) TEC err: this message appears when a loss of communication is detected between the thermometric control unit and the
CFO 521 concentrator. The temperatures shown on the display all appear at 0°C.
4) FO Err: this message appears when it is detected that one or more FO sensors are not working correctly FCC, FOC and
FLT, signals, see sensor diagnostics on page 17.
In case of Err the FAULT relay will be de-energised.
The above messages will be displayed following the 1-2-3-4 priority stated.
LED TEST
We suggest carrying out the control unit LED test regularly.
For this operation, press the TEST key briefly; all the displays turn on for 2 seconds.
If one of the LEDS does not work, please return the control unit to TECSYSTEM for repair.
ALARM RELAY TEST
This function allows you to carry out a test of the relays operation without having to use further devices. To start the test
procedure, press and hold the TEST button for approximately 5 seconds: the TST indication appears for 2 seconds
confirming entry into the Relays Test mode.
The lit LED indicates the relays to be tested, use the cursors to select the desired relay.
Press the SET and RESET keys to energise and de-energise the relay to be tested; the display will show ON-OFF.
After 1 minute's keyboard inactivity, the RELAY TEST procedure will be automatically abandoned.
To stop the RELAY TEST procedure, press the TEST key.
ATTENTION: entering the relay test mode will temporarily disable the fail-safe function, relays with enable function
switch (ALARM-TRIP-FAULT).
ALARM RELAY SILENCING
To silence the ALARM signal, press the RESET key: the relay will de-energise and the ALARM LED, which is on steady, will
start to flash. Silencing is automatically disabled when the temperature goes below the ALARM threshold.

11
FO 935
CONC. CFO 521 / FO SENSORS
The CFO 521 concentrator must be mounted on one side of the transformer, as shown in the image below:
During installation, the following indications must always be observed:
Do not place the concentrator near the hot air flow from the windings or from the core. The operating temperature of the
concentrator ranges from -25°C to 60°C, therefore ensure there is adequate space between the concentrator and the
transformer. Maximum humidity 90% (non-condensing).
The CFO 521 support bracket could facilitate this operation. Always respect the safety distance, suggested by the
transformer manufacturer, from the transformer windings. Fix the bracket, on one of the sides of the transformer, using the
8mm hole with an M8 pin with nut and washer.
DIMENSIONS / INSTALLATION CONC. CFO 521
1MN0226 REV.0
1MN0228 REV.0

12
FO 935
The FO sensors must be inserted inside the secondary winding of the
transformer always respecting the following indications:
•each sensor U-V-W must be inserted inside the secondary
winding transformer, the sensor CH2 must be placed in the
central column.
•insertion of the probe must not find any restrictions or
occlusions of any kind;
•avoid twisting, straining or jerking. The fibre sensors could
be damaged;
•the connection of the sensors to the CFO 521 concentrator
must be laid linearly, with a maximum radius of curvature of
8mm, not less than 90°;
•the connection of the sensors to the CFO 521 concentrator
must be made with the original ST connector supplied with
the sensor.
•any excess of the probes must be wound with a minimum
diameter of 50mm, using the winder located on the
mounting bracket;
•once the probes have been installed, apply the protection
bracket using the M4 screws supplied.
FO (FIBRE OPTIC) TEMPERATURE SENSOR DIMENSIONS/INSTALLATION
READING POINT
ST CONNECTOR
CONNECTION OF THE CONC. CFO 521 / TO THE FO 935 CONTROL UNIT
For correct connection of the CFO 521 concentrator to the thermometric control unit, the following rules must be strictly
observed:
Note: All the signal transportation cables must strictly:
• be separated from those of power
• be created with shielded cable with twisted conductors
• have a section of at least 0.25 mm²
• the shield must be earthed on one side only
• be firmly fixed in the terminal blocks
• have tin-plated or silver-plated conductors
Connect the FO IN input of the CFO521 concentrator to the FO IN input of the FO 935 control unit, respecting the
numbering B1-B2-B3-B4.
The FO OUT output is not used (provision for future development).
The CFO 521 concentrator is powered by the FO 935 control unit, through the FO IN B1-B2-B3-B4 connection bus,
therefore it does not require an external power supply.
1MN0227 REV.0
1MN0228 REV.0
1MN0228 REV.0

13
FO 935
CFO 521 CONCENTRATOR OPERATION
1)
FO IN Input
5)
Dip-switch (not used)
2)
FO OUT output not used
(Provision for future developments)
6)
CH3 fibre optic input
3)
CH4 2/3-wire Pt100 input
7)
CH2 fibre optic input
4)
L1-L2-L3 LED
8)
CH1 fibre optic input
2
1
3
4
5
6
7
8
The CFO 521 device electronically acquires and converts the temperatures detected by the FO sensors CH1-CH2-CH3 and
CH4 (Pt100) and sends the detected data to the FO 935 monitoring unit via the TEC digital communication bus.
The FO (fibre optic) temperature sensors must be connected to the CH1-CH2-CH3 inputs arranged in the three phases of
the U-V-W transformer. For a correct interpretation of the measured values it is advisable to combine the CH2 probe with
the central phase V.
The CFO 521 concentrator has a Pt100 input, RTD class A 2/3-wire probe, for the possible connection of a probe on the
core of the transformer or application of an ambient probe (CH4).
The connection of the Pt100 probe must be 13- White - 14 Red - 15 Red.
The dip-switch must be 000
The LEDs indicate the operating status of the concentrator and of the connected sensors:
• all LEDs OFF signal the lack of power supply on the CFO 521 device.
• Single or multiple LEDs flashing: L1-L2-L3, single flashing every 2 seconds, indicates the correct functioning of channel
CH1-CH2-CH3.
• Single or multiple flashing LEDs: L1-L2-L3, double flashing every 2 seconds, indicates incorrect operation of the reference
channel of channel CH1-CH2-CH3.
1MN0226 REV.0

14
FO 935
Secure the appliance firmly by means of the supplied fixing blocks.
1)
Control unit
2)
Panel hole dimensions (+0.8 mm tolerance)
3)
Identification label
1)
Control unit
3)
Fixing screws
2)
Fixing blocks
4)
Cross-head screwdriver #1X100mm
FO 935 ASSEMBLY
1
2
3
4
1MN0008 REV.0
Drill a hole in the panel sheet with dimensions of 92 x 92 mm.
1
1MN0007 REV.0
2
3

15
FO 935
FO 935 BASIC
FO 935 D
ELECTRICAL CONNECTIONS
1MN0225 REV.0
1MN0224 REV.0
1
2
3
1
2
3
4
1)
Power supply 85-260Vdc-ac 50/60Hz
3)
FO IN bus input for connection to the CFO 521
2)
Relay (ALARM-TRIP-FAULT-FAN1-FAN2)
4)
RS485 Modbus Inside RTU output
1)
Power supply 85-260Vdc-ac 50/60Hz
3)
FO IN bus input for connection to the CFO 521
2)
Relay (ALARM-TRIP-FAULT-FAN1-FAN2)

16
FO 935
Output relays with 10A-250Vca-res COSФ=1 contacts
RELAY CONNECTION EXAMPLE
1MN0095 REV.0
ATTENTION: Before carrying out any electrical test on the transformer or on the panel, e.g. dielectric
strength etc., it is advisable to disconnect all the components of the FO system. Any noise or
voltage peaks on the inputs or on the power supply could cause the failure of: sensors, concentrator
or control unit.
POWER SUPPLY
The FO 935 control unit can be supplied by 85 to 260 Vdc-Vac, 50/60 Hz irrespectively of polarity in Vdc (terminals 40 - 42).
This particularity is obtained thanks to the use of a tested power supply, of new conception and realisation,
which frees the installer from any uncertainty regarding the correct Vac or Vdc power supply.
The earthing cable must always be connected to terminal 41.
When the control unit is powered directly by the secondary of the transformer to be protected, it can be burnt out by high
intensity overvoltages.
These problems occur if the main switch is closed and the transformer does not have the load (no load test).
The above is much more evident when the 220 Vac voltage is taken directly from the bars of the secondary
of the transformer and there is a fixed capacitor battery for power factor correction of the transformer itself.
To protect the control unit against line overvoltages, the PT-73-220 electronic arrester,designed by TECSYSTEM S.r.l. for
this specific purpose, is recommended. Alternatively, it is advisable to use power supply voltages 110 Vac or, even better,
110 Vdc.
If an existing control unit must be replaced with a new one, to guarantee its correct and safe operation, the
sensor/relay/supply connecting terminals must be replaced with the new terminals supplied.
AUDIBLE AND VISUAL
INDICATION
ALARM CONDITION
SYSTEM
SHUTDO
WN
Note: image relay contacts in non-alarm condition, except for the FAULT relay which switches: contacts 10–11
closed (NO) contacts 9-11 open (NO) fault condition identification. Read paragraph Alarms and Ventilation p. 17 and
see image of fault contact switching.

17
FO 935
ALARMS AND VENTILATION
Carry out the electrical connections on the removable terminal blocks only after disconnecting them from the unit.
When the control unit is in one of the modes indicated below it does not perform any thermal monitoring, moreover the
relays will all be disabled. The fault contact switches and the fault LED flashes.
•Programming viewing display.
•PRG programming.
•Relay test.
The ALARM and TRIP relays only switch when the set temperature thresholds are exceeded.
The FAULT (fault) contact, programmed in active failsafe mode (default YES), opens (11-12) when the appliance is
powered, only if during the access phase the control unit does not detect anomalies, and keeps the switching until when
one of the following events occurs:
•Data memory fault (Ech message).
•FO sensor fault (FCC-FOC-FLT)
•CFO 521 concentrator disconnected (TEC)
•Insufficient supply voltage.
•During the power on reset after programming (PRG), displaying of the data (VIS) and relay test.
The FAULT failsafe mode can be disabled FAULT failsafe "NO" see programming step 30-31 page 20.
NOTE: in order to avoid unwanted system outages, do not connect the FAULT relay to the transformer tripping circuit.
FAULT AND RESET MESSAGE SEQUENCE
Find below the sequence of fault messages and RESET function condition.
1) ECH
2) TEC
3) FO FCC
4) FO FOC
5) FO FLT
The FAN1 and FAN2 contacts can be used to control the cooling fans, or they can be inserted in the conditioning system
of the transformer room, see paragraph cooling fan control on page 18.
NOTE: always disconnect the unit before performing any electrical connections.
eeprom fault
concentrator communication bus fault
min. temperature full scale exceeded
max. temperature full scale exceeded
broken or disconnected fibre optic sensor
erasable message
non-resettable condition
non-resettable condition
non-resettable condition
non-resettable condition
FO SENSOR DIAGNOSTICS
In case of breakage or exceeding of the minimum/ maximum full scale value of one of the FO sensors installed on the
machine to be protected, the FAULT relay is instantaneously switched, with the relative sensor failure indication on the
corresponding channel.
Display message FCC: exceeding of the minimum full scale value = measured temperature <-35°C
Display message FOC: exceeding of the maximum full scale value = detected temperature > 195°C
ATTENTION: the FLT indication appears on the display when the concentrator identifies a faulty or disconnected FO
sensor.
To eliminate the message and to restore the Fault switching, check the connections of the FO sensors and replace the faulty
sensor if necessary. In case the minimum/maximum full scale value has been reached, make sure that the environmental
conditions correspond to what is indicated by the control unit.
Note: exceeding of the minimum/ maximum full scale can also be caused by possible disturbances on the communication
lines or by strong magnetic fields; in this case, the following is recommended:
Check the correct installation of the sensors and especially of the extension cable between the CFO 521 concentrators and
the FO 935 control unit.
FAULT CONTACT OPERATION (failsafe active)
FAULT 11-12 NC: ALARM FAULT OR POWER OFF
FAULT 11-12 NO: POWER ON OR NO FAULT

18
FO 935
PROGRAMMED DATA DIAGNOSTICS
In case of failure of the internal memory or corruption of programmed data, just after switching on, Ech appears with the
relevant Fault contact signal.
In this case, for safety reasons, the default parameters are loaded automatically (see programming table on pages 19-20).
Eliminate the Ech indication by pressing RESET and run programming to enter the desired values.
Finally switch the unit off and back on to check the memory works correctly, if it is damaged Ech will be displayed again
(send the control unit to TECSYSTEM srl for repairs).
TEMPERATURE DIAGNOSTICS
When one of the sensors detects a temperature higher than 1°C with respect to the pre-set value as the alarm limit, after
approximately 5 seconds the ALARM relay switches and the channel ALARM LED (CHn) switches on.
When the trip temperature limit is exceeded, after approximately 5 seconds the TRIP relay switches and the channel TRIP
LED (CHn) switches on.
As soon as the recorded temperature returns to values equal to or lower than the limit set for the ALARM and TRIP relays
switching, these relays de-energise and the corresponding LEDs switch off.
The values of ALARM and TRIP are kept in the internal memories: they can be recalled by entering the Vis modes
(displaying programmed parameters) and modifiable in the PRG mode (programming).
COOLING FAN CONTROL
The FO 935 control unit is fitted with two FAN contacts (FAN1 and FAN2) and, if programmed correctly, can control the fans
switching ON and OFF to cool the transformer.
The FAN1 and FAN2 contacts can manage cooling the transformer and the room where it is installed.
Connecting FAN1 to the tangential ventilation system (the two bars located on the transformer) and FAN2 to the extractor
will improve the air flow in the cabin; furthermore, the cabin temperature will no longer need to be managed by a thermostat
that is external to the system.
The fans can be controlled in two different ways:
• Using the temperatures sensed by the sensors on the three columns
CHF 1.2.3 (e.g.ON at 70°C - OFF at 60°C)
• Through an additional sensor (CH4/YES) dedicated to the ambient temperature inside the transformer room.
CHF 4 (e.g.ON at 40°C - OFF at 30°C)
The ON and OFF values are programmable according to the device range. The FAN ON must always be at least 1°C higher
than FAN OFF (recommended ΔT FAN ON_OFF +10°C).
The FAN 1/ 2 LED lights up when the temperature exceeds 1°C, the FAN ON threshold, the corresponding relay switches,
and turns off when the temperature goes below 1°C the FAN OFF threshold, the corresponding relay switches.
FAN TEST
It is possible, by programming (HFn), to make sure that the fans are operated for 5 minutes every xxx” hours, regardless of
the temperature values of the columns or the environment (e.g.: with HFn = 001 the fans are activated for 5 minutes every
hour).
This function is designed to periodically check the operation of the fans and of their control equipment.
Setting NO, this function is inhibited.
To enable the HFN function, read the programming section on pages 19-20.

19
FO 935
STEP
PRESS
EFFECT
PRESS
NOTES
1
Press and hold the PRG button until the display shows
SET PRG
2
Select PRG SET to proceed with programming or PRG 1
to load the default values
PRG 1 default data
3
The ALARM threshold for (CH 1-2-3) is displayed.
Set the desired threshold, the Alarm LED flashes
Default 90°C
4
The TRIP threshold for (CH 1-2-3) appears and the Trip
LED flashes.
5
Set the desired threshold
Default 119°C
6
CH 1-2-3 is displayed
The Fan1 LED flashes
Default YES
7
Select YES/NO
8
The display shows (CH4)
Enabling CH4
9
Select YES or NO
with YES the CH4 is enabled
with NO the CH4 is disabled
10
The ALARM threshold for (CH4) appears and the Alarm
LED flashes.
If CH4=NO jump to step 16,
Default NO
11
Set the desired threshold
Default 120°C
12
The TRIP threshold for (CH4) is displayed.
The TRIP LED flashes
13
Set the desired threshold
Default 140°C
14
The display shows FAN 2 for (CH4)
Default Yes
15
Select YES/NO
16
The display shows ON (CH 1-2-3),
the FAN1 LED flashes
Default 70°C
17
Set the desired threshold FAN1 ON
If FAN1 NO is selected skip to
step 21
18
The display shows OFF (CH 1-2-3),
the FAN1 LED flashes
Default 60°C
19
Set the desired threshold FAN1 OFF
PROGRAMMING
FO 935 BASIC/D

20
FO 935
20
The display shows ON (CH4),
the FAN 2 LED flashes
Default 45°C
21
Set the desired threshold FAN2 ON
If FAN2 NO is selected skip to step
24
22
The display shows OFF (CH4)
the FAN2 LED flashes
Default 35°C
23
Set the desired threshold FAN2 OFF
24
HFN (NO) is displayed
The FAN1-FAN2 LEDs flash
Fan cyclic test
for 5 min. every “n” hours
25
Set the desired number of hours
Default NO = function
disabled
26
FLS (ALARM) is displayed
Blinking ALARM LED
(FAIL SAFE info on page 21)
27
Select YES or NO
Default NO
28
FLS (TRIP) is displayed
Blinking TRIP LED
29
Select YES or NO
Default NO
30
FLS (FAULT) is displayed
Blinking FAULT LED
31
Select YES or NO
Default YES
For version FO 935 (BASIC) skip to step 38
32
ADR <>"datum" is displayed
Modbus address
Default 001
33
Set the address
1 to 255
34
BDR <>"datum" is displayed
Modbus transmission speed
Default 19.2 Kb/s
35
Set the desired speed
From 2.4 Kb/s to 38.4 Kb/s
36
PAR <>"datum" is displayed
Parity bit selection. EVE Default
37
Set the desired parity bit
None (N-1 or N-2),
Even (EVE),
Odd (ODD)
See frame DATA on page 22.
38
END is displayed
End of programming;
39
Press ENT to save the set data
and exit programming
incorrect programming of the LED
values indicated (note 6)
40
Return to step 1
See programming notes p. 21