TECSYSTEM NT935 User manual

1MN0102 REV. 0
operates with ISO9001 certified quality system
R. 1.6 15/03/17
“Translations of the original instructions”
ENGLISH
NT935
INSTRUCTION MANUAL

2
NT935
ASERIES
PAGE
1) SAFETY REQUIREMENTS
……….......................................
4
2) ACCESSORIES
…………………………………..
5
3) TECHNICAL SPECIFICATIONS
…………………………………..
6
4) FRONT PANEL
…………………………………..
8
DISPLAY
…………………………………..
9
OPERATING PROGRAM CONTROL
………………………………….
—
NOTES ON SCAN AND MAN FUNCTIONS
…………………………………..
—
LED TEST
…………………………………..
—
ALARM RELAY TEST
…………………………………..
—
ALARM RELAY SILENCING
…………………………………..
—
5) MOUNTING
…………………………………..
10
6) ELECTRICAL CONNECTIONS NT935 BASIC
…………………………………..
11
NT935 AD BACK
…………………………………..
12
POWER SUPPLY
…………………………………..
13
ALARMS AND VENTILATION
…………………………………..
—
FAULT AND RESET MESSAGE SEQUENCE
…………………………………..
—
7) PROGRAMMING
…………………………………..
14
NT935
…………………………………..
—
PROGRAMMING NOTES
…………………………………..
16
TEMPERATURE SENSORS
…………………………………..
—
MEASUREMENT SIGNAL TRANSFER
…………………………………..
—
TEMPERATURE SENSOR DIAGNOSTICS
…………………………………..
17
VOTING FUNCTION
…………………………………..
—
PROGRAMMED DATA DIAGNOSTICS
…………………………………..
—
TEMPERATURE DIAGNOSTICS
…………………………………..
—
COOLING FAN CONTROL
…………………………………..
18
FAN TEST
…………………………………..
—
INTELLIFAN FUNCTION
………………………………….
—
CONTENTS
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 VALID AND COMPLETE FOR THE NT935 BASIC AND NT935 AD CONTROL
UNITS

3
NT935
SERIES
PAGE
8) RS485 MODBUS
…………………………………..
19
INTRODUCTION TO THE MODBUS INSIDE
MODULE
…………………………………..
—
OPERATING NOTES
…………………………………..
—
DATA TRANSMISSION ON MODBUS NETWORK
…………………………………..
—
RS485 ELECTRICAL CONNECTIONS
…………………………………..
—
DATA FRAME
…………………………………..
—
DATA PACKET
…………………………………..
—
FUNCTION CODE
…………………………………..
20
CODE 3(10).
…………………………………..
—
CODE 16(10).
…………………………………..
—
NOTES FOR REMOTE PROGRAMMING
…………………………………..
—
ERROR CODES
…………………………………..
21
UNACCEPTABLE DATA
…………………………………..
—
ILLEGAL DATA
…………………………………..
—
POLLING FREQUENCY
…………………………………..
—
MODBUS MAPPING TABLE
…………………………………..
22
9) FAIL SAFE FUNCTION
…………………………………..
27
10) OUTPUT 4.20mA
…………………………………..
—
11) TECHNICAL SPECIFICATIONS OF THE EXTENSION
CABLE FOR Pt100
…………………………………..
—
12) FCD FUNCTION
…………………………………..
28
13) WARRANTY CONDITIONS
…………………………………..
—
14) TROUBLESHOOTING
…………………………………..
29
15) EQUIPMENT DISPOSAL
…………………………………..
—
16) USEFUL CONTACTS
…………………………………..
—
17) UL SPECIFICATION AND RATINGS
…………………………………..
30

4
NT935
ASERIES
SAFETY REQUIREMENTS
ATTENTION :
Carefully read the manual before starting using the control unit. Keep the instructions for future reference.
Do not open the device, touching any internal component can result in electric shock as voltages over 50 volts
can be lethal. In order to reduce the risk of electric shock, do not disassemble the back of the device. Warranty shall be
void if device is opened.
Before connecting the device to the power supply, ensure that all the connections are correct. Always disconnect
the unit from the supply before making any modification on the wiring.
Any operation on the equipment must be operated by a qualified technician.
Failure to comply with these instructions can cause damages, fires or electric shock, and possible serious
injuries!
POWER SUPPLY
The NT935 series control unit has UNIVERSAL power supply, i.e. it can be supplied at 24 to 240 Vac-Vdc, irrespectively
of polarity in Vdc. Before use, ensure that the power cable is not damaged, knotted or pinched. Do not tamper with the
power cable. Never disconnect the unit by pulling the cable, avoid touching the clamps. Do not carry out any
connecting/disconnecting operation 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 technical service.
LIQUIDS
Do not expose the equipment to liquid spurts or drops, do not position it in places where humidity exceeds 90% and
never touch it with wet or humid hands during storms. If any liquid penetrates the control unit, disconnect immediately
and contact technical service.
CLEANING
Disconnect the power cable before cleaning the control unit, using a dry cloth without any solvent or detergent, and
compressed air.
OBJECTS
Never insert objects into the openings of the control unit. If this happens, disconnect the control unit and contact technical
service.
USE RESERVED TO QUALIFIED PERSONNEL
The purchased good is an advanced electronic device that should not be used by non-qualified personnel. Any operation
must be carried out by a qualified technician.
ACCESSORIES
The use of non-original accessories or spare parts may damage the unit and endanger users' safety. In event of fault,
contact technical service.
LOCATION
Install the control unit indoor, in a place protected from water splashes and sun rays. Do not place near heat sources if
exceeding the parameters stated in this manual. Position on a stable surface, far from any possible vibrations. Position
the unit as far as possible from intense magnetic fields..
REPAIRS
Do not open the control unit. In case of fault, always contact qualified personnel. The opening of the control unit and/or
the removal of the series identifying label automatically make the warranty void. The warranty seal is applied to all
devices, any attempt to open the unit would cause the seal to break the consequent automatic cancellation of the
warranty.
FUNCTION
To control the transformer correctly from a temperature point of view, enabling the VOTING function is allowed
where the load distributed between the phases of the transformer is adequately balanced.

5
NT935
SERIES
Tthe following object are present inside the box :
Control unit
Start guide and QR code
2 blocks for panel mounting
1 supply terminal 3 poles pitch 5
Code: 2PL0367 - Screws tightening torque 0.5Nm
1 relay terminal 12 poles pitch 5
Code: 2PL0361- Screws tightening torque 0.5Nm
1 Pt100 sensor terminal 12 poles pitch 3.81
Code: 2PL0420 - Screws tightening torque 0.25Nm
1 terminal 2 poles pitch 5 for 4.20mA output (*)
Code: 2PL0364 or 2PL0363
Screws tightening torque 0.5Nm
1 RS485 terminal 3 poles pitch 3.81 (*)
Code: 2PL0366 - Screws tightening torque 0.25Nm
(*) only for NT935 AD version
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 might cause malfunctions.

6
NT935
ASERIES
TECHNICAL SPECIFICATIONS
NT935 BASIC NT935 AD
POWER SUPPLY
Supply rated values 24-240 Vac-Vdc
50/60HZ 24-240 Vac-Vdc
50/60HZ
Maximum and minimum supply values 20-270 Vac-Vdc
50/60HZ 20-270 Vac-Vdc
50/60HZ
Vdc with reversible polarities
●
●
INPUTS
4 inputs for RTD sensors, Pt100 type with 3 wires (max section 1.5mm²)
●
●
Connections on removable terminal strips
●
●
Input channels protected
against
electromagnetic
interference
●
●
Cable compensation for thermistors
500 m (1 mm²)
500 m (1 mm²)
OUTPUTS
2 alarm
relays
(ALARM AND TRIP) SPDT
●
●
1 sensor or operating failure (FAULT) relay SPST
●
●
Output relays with 10A-250Vac-res COSФ=1 contacts.
●
●
2 ventilation management relays SPST FAN 1 AND FAN 2
●
●
Modbus RTU RS485 output
NO
●
Optically
isolated 4.20 mA output
NO
●
DIMENSIONS
100x100 mm–din43700-depth 131mm (terminal block included)
Hole 92 x 92 mm
Hole 92 x 92 mm
TESTS AND PERFORMANCE
Construction in compliance with CE regulations
●
●
Protection from electrical interference EN 61000-4-4 ●●
Dielectric strength 1500 Vac for a min. between output relays and
sensors, relays and power supply, power supply and sensors
●
●
Accuracy ±1% vfs, ±1 digit
●
●
Ambient
operating
temperature from –20°C to +60°C
●
●
Humidity
90% non-
condensing
●
●
Front polycarbonate IP65 ●
●

7
NT935
SERIES
(*)On demand, available version from -40°C to 200°C with alarm temperature management range from 0°C to 200°C
TECHNICAL SPECIFICATIONS
NT935 BASIC NT935 AD
Housing
NORYL 94 _V0 ●●
Absorption 7,5VA ●●
Data memory 10 years minimum ●●
Digital
linearity
of sensor
signal
●●
Self-diagnostic circuit ●●
Protection treatment of the electronic part
Option
Option
DISPLAY AND DATA MANAGEMENT
2x13mm 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 0°C to 240°C (*) ●●
2 alarm thresholds for channels 1-2-3 ●●
2 alarm thresholds for channel 4 ●●
2 ON-OFF thresholds for FAN 1 and FAN 2 ●●
Sensor
diagnostics
(Fcc-Foc-Fcd) ●●
Data memory diagnostics (Ech) ●●
Access to
programming
through
front
keyboard
●●
Automatic exit from relay programming, display and test after 1
minute's inactivity ●●
Incorrect
programming
warning
●●
Selection between channel automatic scanning, hottest channel or
manual scanning ●●
Storage of maximum temperatures reached by channels and alarm
status ●●
Front key to reset the alarms ●●
Voting
function ●●
Intellifan function ●●
Failsafe function ●●

8
NT935
ASERIES
1) 3-digit temperature display 12) Enter/Reset button
2) Control unit series 13) Programming / Setting key
3) TRIP (red) LED 14) LED/relay test key
4) ALARM (yellow) LED 15) Modbus RS communication (green) LED (only AD)
5) FAULT (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 block 20) Scan mode selection (yellow) LED
10) UP key 21) Fixing block
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
1MN0102 REV. 0
21

9
NT935
SERIES
DISPLAY
The first display is dedicated to temperatures
The second display to the monitored channel.
When switching the device ON or following a reset, the display shows the NT935 control unit model : BAS (no option) or
AD, VER "00" (firmware version) and temperature range.
Pressing the MODE key, the display modes can be set:
SCAN: the monitoring unit displays all the activated (°C) and deactivated (NO) channels scanning every 2 seconds.
AUTO: the monitoring unit displays the hottest channel automatically.
MAN: manual reading of the channel temperature using the up/down .
T.MAX: the monitoring unit displays the highest temperature reached by the sensors and any situation of: alarm or fault
occurred after the last reset. Select channels with cursors , reset values with RESET.
OPERATING PROGRAM CONTROL
To control the protection levels programmed, press the PRG key twice to access the VIS display mode. By 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 NT935 can be displayed.
1) RUN cPU:
This message appears when the unit operates regularly without any system error.
2) Ech Err:
This message appears when a 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 14-15. Return the control unit to TECSYSTEM for repair.
3) CAL Err:
This message appears when damage is found in the measurement circuit.
The temperature values displayed might be incorrect. Return the control unit to TECSYSTEM for repair.
4) Pt Err :
This message appears when it is detected that one or more PT100 sensors are not working correctly, FOC, FCC
and FCD indications in the temperature sensor diagnostics paragraph 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.
NOTE: regardless of the display mode, in case of a sensor fault (fcc, foc or fcd), the control unit will automatically switch to
SCAN (PRIVILEGED SCAN) mode, immediately allowing you to see the fault on the relative channel CH.(Mode key is
disabled).
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 relay operation without having to use further devices. To start the test
procedure, keep the TEST button pressed for about 5 seconds: TST appears for 2 seconds, confirming you have entered the
Relay Test mode.
The LED that is lit shows the relay 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.
Alternatively, you can use the PT100 simulator model: SIM PT100.
ALARM RELAY SILENCING
If you want to silence the ALARM signal press the RESET key: the relay de-energises and the ALARM LED, which was
fixed, will start flashing. Silencing is automatically disabled when the temperature goes below the ALARM threshold.

10
NT935
ASERIES
Fix the unit securely with the blocks supplied.
1) Control unit 2) Panel hole dimensions (+0.8mm tolerance)
3) Identification label
1) Control unit 3) Fixing screw
2) Fixing block 4) Crosshead screwdriver #1X100mm
MOUNTING
1
1MN0007 REV. 0
2
3
1
2
3
4
1MN0008 REV. 0
Drill a 92 x 92 mm hole in the panel sheet.

11
NT935
SERIES
NT935 BASIC
SCREEN
RED
RED
WHITE
Note: relay contact image in non-alarm condition, with the exception of the FAULT relay that opens: contacts 11-12
open (NO) contacts 11-12 closed (NC) fault condition identification. Read the Alarms and Ventilation paragraph on
page 13
3 and see the opening of the fault contact.
ALARM
CONDITION AUDIO AND
VISUAL INDICATION
STOP
SYSTEM
Pt100 CONNECTION EXAMPLE
Note: before connecting the
sensors to the control unit, read
the Measurement signal transfer
paragraph on page 16.
Output relay with 10A-250Vac-res COSФ=1 contacts.
COSФ=1.
1) Pt100 sensors (white-red-red) 3) Relays (FAN2-FAN1-ALARM-TRIP-FAULT)
2) Supply 24-240Vac-dc 50/60Hz.
ELECTRICAL CONNECTIONS
1MN0095 REV. 0
2
3
1
RELAY CONNECTION EXAMPLE

12
NT935
ASERIES
NT935 AD
1) Pt100 sensors (white-red-red) 3) Relays (FAN2-FAN1-ALARM-TRIP-FAULT)
2) Supply 24-240Vac-dc 50/60Hz. 4) Output 4.20 mA
5) Modbus RTU RS485 output
SCREEN
RED
RED
WHITE
ELECTRICAL CONNECTIONS
5
1
2
3
4
1MN0095 REV. 0
Output relay with 10A-250Vac-res COSФ=1 contacts.
COSФ=1.
STOP
SYSTEM
ALARM
CONDITION AUDIO AND
VISUAL INDICATION
Pt100 CONNECTION EXAMPLE
Note: before connecting the
sensors to the control unit, read
the Measurement signal transfer
paragraph on page 15.
Note: relay contact image in non-alarm condition, with the exception of the FAULT relay that opens: contacts 11-12
open (NO) contacts 11-12 closed (NC) fault condition identification. Read the Alarms and Ventilation paragraph on
page 13 and see the opening of the fault contact.
RELAY CONNECTION EXAMPLE

13
NT935
SERIES
POWER SUPPLY
The NT935 control unit has UNIVERSAL power supply, i.e. it can be supplied by 24 to 240 Vac-Vdc, 50/60Hz irrespectively
of polarity in Vdc (terminals 40-42).
This is obtained thanks to the use of a tested power supply unit, newly designed and manufactured, that frees installers from
worrying about the correct Vac and Vdc supply.
The ground must always be connected to terminal 41.
When the unit is supplied directly by the secondary of the transformer to protect, it can be burnt out by strong
overvoltages.
This happens if the main switch is closed and the transformer has no load (blank test).
The above-mentioned problems are much more evident when the 220 Vac voltage is taken directly from the transformer
secondary bars and there is a fixed capacitor battery to phase the transformer itself.
To protect the control unit from line overvoltages, we suggest using the PT-73- 220 electronic discharger, designed by
TECSYSTEM S.r.l. for this specific purpose. As an alternative we suggest using 110 Vac or, even better, 110 Vdc supply
voltages.
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.
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 mentioned below, it does not monitor the temperature and the relays are all
blocked, the FAULT led start blinking.
Vis. programming display
PRG programming
Relay test
The ALARM and TRIP relays switch only when the set temperature thresholds are exceeded.
The FAULT contact, programmed in failsafe mode (default YES), opens (11-12) when the equipment is supplied only if
the unit detects no fault on switching on, and stays in this condition until one of the following events occurs:
Data memory fault (Ech message).
Pt100 sensor fault (FCC short-circuited sensor, FOC interrupted sensor or Fcd quick temperature increase)
CAL damage to the measurement circuit.
Insufficient supply voltage.
During the power on reset after programming (PRG), displaying the data (VIS) and test relay.
The FAULT failsafe can be disabled selecting FAULT failsafe "NO" see step 34-35 programming page 15.
NOTE: do not connect the FAULT relay to the transformer tripping circuit to avoid unwanted system interruptions.
FAULT AND RESET MESSAGE SEQUENCE
Find below the sequence of fault messages and RESET function condition.
1) ECH
2) CAL
3) FCD
4) ERR PT
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 Fan control on page 17.
NOTE: always disconnect the unit before performing any electrical connections.
11 12
FAULT 11-12 NC: ALARM FAULT OR POWER OFF
FAULT 11-12 NO: POWER ON OR NO FAULT
11 12
FAULT CONTACT OPERATION (failsafe enabled)
eeprom fault
measurement circuit fault
quick temp. increase fault
FCC or FOC sensor fault
erasable message
erasable message
resettable condition
non-resettable condition

14
NT935
ASERIES
PROGRAMMING
NT935 BASIC/AD
STEP PRESS EFFECT PRESS NOTES
1 Keep the PRG key pressed until the display shows PRG
2 Select PRG SET for entering in the programming mode or
PRG 1 to restore the default programmed value. PRG 1 default value
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) is displayed and the
Trip LED flashes.
5 Set the desired threshold Default 119°C
6 FAN1 (CH 1-2-3) is displayed and the Fan1 LED flashes. Default YES
7 Select YES / NO / INT If you select INT, read the
function notes on page 18
8 (CH4) is displayed
CH4 enabling
9 Set YES or NO with YES CH4 is enabled
with NO CH4 is disabled
10 The ALARM threshold for (CH4) is displayed, the Alarm
LED flashes. If CH4=NO go 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 FAN2 for (CH4) is displayed Default Yes
15 Select YES or NO
16 ON (CH 1-2-3) is displayed and the FAN1 LED flashes. Default 70°C
17 Set the desired FAN1 ON threshold
If you select FAN1 NO, go
to step 21 if you select
INT the FAN1 and FAN2
LEDs flash.
18 OFF (CH 1-2-3) is displayed, the FAN1 LED flashes Default 60°C
19 Set the desired FAN1 OFF threshold
20 ON (CH4) is displayed, the FAN2 LED flashes Default 45°C
21 Set the desired FAN2 ON threshold If you select FAN2 NO,
go to step 24

15
NT935
SERIES
22 OFF (CH 4) is displayed, the FAN2 LED flashes Default 35°C
23 Set the desired FAN2 OFF threshold
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 FCD (NO) is displayed Fault for quick temperature
increase (°C/sec)
27 Set the desired value
(See FCD info on page 28) Default NO
(function excluded)
28 VOT (NO) is displayed
(See VOTING on page 17)
29 Set YES or NO
Default NO
(function excluded)
30 The display shows FLS (ALARM) flashing LED ALARM
(info FAIL SAFE on page 27)
31 Set YES or NO Default NO
32
The display shows FLS (TRIP) LED flashes TRIP
33 Set YES or NO
Default NO
34
The display shows FLS (FAULT) LED flashes FAULT
35 Set YES or NO
Default YES
36 For NT935 (BAS) version jumps to step 45
37
ADR <> "datum" is displayed
Modbus address
Default 001
38 Set the address
From 1 to 255
39
BDR <> "datum" is displayed
Modbus transmission speed
Default 19.2 Kb/s
40 Set the desired speed
From 2.4 Kb/s to 38.4 Kb/s
41
PAR <> "datum" is displayed Parity bit selection Default EVE
42 Set the desired parity bit
None (N-1 or N-2), Even (EVE),
Odd (ODD)
See Data frame at page 19
43
420 <> "datum" is displayed 4.20 mA output programming
44 Select the 4.20 mA output desired
1-2-3-4; fixed channel
SCA: scanning
HOT: the hottest channel
Default HOT
45 END is displayed End of programming
46 Press ENT to save the set data
and exit programming Err: incorrect programming of
the LED values (note 6)
47 Return to step 1 See programming notes on page
16

16
NT935
ASERIES
ATTENTION :
We recommend you check the unit's programming before starting the device.
The default parameters set by TECSYSTEM might not match your requirements.
Programming the device is the end user's responsibility, the settings of the alarm thresholds and the enabling of
the functions described in this manual must be checked (by a specialized engineer) according to the application
and features of the system the control unit is installed on.
TEMPERATURE SENSORS
Each Pt100 thermometric sensor has one white and two red connectors (CEI 75.8 regulations).
The CH2 channel must be always referred to the central column of the transformer.
The CH4 channel must be always referred either to the core of the transformer or to the Pt100 ambient sensor if you wish to
thermo-regulate the transformer room using the NT935 control unit.
MEASUREMENT SIGNAL TRANSFER
All the cables transferring the Pt100 measurement signals must comply with the following under all circumstances:
1. Every Pt100 must be connected with a three-wire cable having a minimum section of 0.50mm² and a maximum of 1 mm².
2. The extension cable must be screened with tinned copper braid with an 80% cover
3. Conductors must be twisted, maximum recommended step 60mm
4. The cable screening must be grounded only with a termination, preferably on the unit side.
5. The sensors' signal transfer cable must not be near electrical cables, either low or medium-high voltage.
6. The Pt100 cable and the signal transfer cable must be laid in a straight line, without any winding.
7. Any caps used to butt conductors must be crimped properly to avoid false contacts.
NOTE: to install the sensors and signal transferring cable correctly, read the SCS/SENSOR installation rules
manual.
What may happen when installation rules are not complied with.
The electrical field propagating from the power line of another circuit, couples capacitively with the conductors (in particular
with unscreened cables). The effect of this coupling creates a signal that overlaps the signal transmitted by the nearby
conductors, causing incorrect readings.
2) The variations in magnetic flux in the power lines may induce an electromotive force on the signal transferring cables (in
particular non-twisted cables), that, being a closed circuit, generates a current. This interference current, multiplied by the
circuit resistance, gives a voltage value that overlaps the signal to be transmitted, distorting the sensor measurement.
3) False contacts can alter the signal with the consequent variation in the temperature detected.
In specific cases, when the rules for connecting the Pt100 sensors are not complied with, the following anomalies can
occur between the SCS box and the temperature control unit:
a) incorrect temperature readings, alarms or anomalous tripping
b) mechanical / electrical fault of the Pt100 sensors
c) damage to the Pt100 inputs of the control unit.
TECSYSTEM S.r.l. has designed its own special cable to transfer the measurement signals, CEI-compliant, with all the
protection requirements provided for: model CT-ES
PROGRAMMING NOTES
1) The MODE key allows reversing the programming steps according to the sequence 28-26-8-1.
2) The TEST key allows exiting programming without saving the modified data.
3) After 1 minute's keyboard inactivity programming is abandoned without saving the data.
4) During programming the control unit does not control/protect the monitored machine.
5) At the end of programming the control unit is restarted and the FAULT relay is disabled until the unit is fully restarted.
6) If pressing ENT, “Err” appears, it means that one of the following mistakes has been made:
ERR ALL. = ALARM ≥TRIP
ERR FAN = FAN-OFF ≥FAN-ON. (FAN1 OR FAN2)
ERR INT = INT FAN-OFF ≥FAN-ON (FAN1) DELTA <10°C
The device automatically switches to the programming step of the mistake.
NOTE: EVERY TIME THE CONTROL UNIT IS PROGRAMMED WITH DATA SAVING CONFIRMATION, THE VALUES
STORED IN T-MAX ARE RESET TO THE TIME OF SAVING.

17
NT935
SERIES
NOTE: the use of cables not complying with the above might cause reading anomalies. It is always important to
take into account that any interference on the signal lines might cause anomalies on the Pt100 inputs (CH1-
CH2-CH3-CH4...) or on the sensors themselves.
TEMPERATURE SENSOR DIAGNOSTICS
In case of failure or exceeded full scale value of one of the thermometric sensors installed on the machine to protect, the
FAULT relay opens immediately with the relative warning of faulty sensor on the corresponding channel (PT err).
Fcc indicates sensor short-circuited or minimum full scale value of the control unit exceeded -8°C (version 0°÷240°C)
and -48°C (version -40°C÷200°C)
Foc indicates sensor interrupted or maximum full scale value of the control unit exceeded 243°C (version 0°÷240°C)
and 203°C (version -40°C÷200°C)
To eliminate the message and reset the opening of the Fault contact, it is necessary to check the Pt100 connections and
replace the faulty sensor (if any). If the minimum/maximum full scale value has been reached, check that the ambient
conditions match the control unit reading.
Note: exceeding the minimum/maximum full scale value can also be caused by interference on the sensor lines; in this
case we recommend that you check:
the correct installation of the sensors and above all of the extension cable (as stated in the paragraph MEASUREMENT
SIGNAL TRANSFER)
the activation of: VOTING (see below) or FCD (see page 28) must always be operated taking into account the system
working conditions.
CAL message display: it appears when damage is found in the measurement circuit. The temperature values displayed
might be incorrect. Return the control unit to TECSYSTEM for repairs.
VOTING FUNCTION
The voting function derives from the redundancy concept that consists in duplicating the components of a system to
increase their reliability.
How does VOTING work?
Using the redundancy principle, we use the sensors installed on the three phases U-V-W to monitor the transformer's
operation, and at the same time ascertain the sensors are working correctly, discriminating against any false alarms
(generated by installation errors).
By activating the VOTING "YES" function, the control unit compares the temperature values recorded on the monitored
CH1-CH2-CH3 channels and enables the switching of the TRIP contact only if the TRIP threshold has been exceeded on
at least two channels over the same period T.
By selecting VOTING “NO” the function will be disabled.
Note: by setting Voting "Yes" the switching of the ALARM contact will anyway indicate the alarm threshold on each
individual channel has been exceeded.
To enable the Voting function, read the programming section on pages 14-15.
Attention: To control the transformer correctly from a temperature point of view, enabling the VOTING
function is allowed where the load distributed between the phases of the transformer is adequately
balanced. In addition, any conditions of FAULT: FCC-FCC-FCD on two or more channels, with active
voting, can determine the TRIP contact inhibition.
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.
In this case, for safety reasons, the default parameters are loaded automatically (see programming table on pages 14-15).
Eliminate Ech 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 temperature sensors senses a temperature 1°C higher than the alarm threshold, 5 seconds later the
ALARM relay switches and the ALARM LED of the affected channel (CHn) lights up.
When the trip temperature limit is exceeded, the TRIP relay switches and the TRIP LED of the affected channel (CHn)
lights up.
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 ALARM and TRIP values are kept in the internal memory: they can be recalled by entering the Vis modes
(programmed parameter display) and modified in PRG (programming) mode.
All "NT" series control units have linearity of the sensor signal, with a maximum error of 1% of full scale value.

18
NT935
ASERIES
COOLING FAN CONTROL
The NT935 control unit is fitted with two FAN controls (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.
By connecting FAN1 to the tangential cooling system (the two bars on the transformer) and FAN2 to the extractor, you will
improve the air flow in the cabin; moreover, the cabin temperature will no longer need to be managed by a thermostat
outside the system.
The fans can be controlled in two different ways:
Using the temperatures sensed by the sensors on the three columns (FAN1)
CHF 1.2.3
(ex. ON at 70°C - OFF at 60°C)
Via an extra sensor (CH4/YES) dedicated to the ambient temperature inside the transformer room (FAN2).
CHF 4
(ex. ON at 45°C - OFF at 35°C)
The ON and OFF values are programmable according to the device range. FAN ON must always be greater by at least
1° C since FAN OFF (recommended ΔFAN (POWER ON-OFF) + 10 ° C).
The FAN 1 / FAN 2 LED lights up when the temperature exceeds the FAN ON threshold, the corresponding relay
switches, and turns off when the temperature goes below the FAN OFF threshold, the corresponding relay switches
FAN TEST
By programming (HFn), it is possible to have the fans operating 5 minutes every "xxx" hours, regardless of the column or
ambient temperature values (i.e.: with HFn=001 the fans are activated for 5 minutes every hour).
This function aims at verifying the fan operation and their control apparatus periodically.
By setting NO this function is inhibited.
To enable the Hfn function, read the programming section on pages 14-15.
INTELLIFAN FUNCTION
What it is used for:
The Intellifan function allows reducing the transformer's thermal shock by partially anticipating (one bar at the time) the
activation of the tangential ventilation system.
The reduction in the transformer's thermal shock will extend the life of the transformer and of the ventilation system itself.
By enabling the FAN 1 "INT" function, the control unit will alternate the activation (each 30 minutes) of the FAN1 and
FAN2 contacts, anticipating the activation of the ventilation system at the intermediate value included between FAN1 ON
and FAN1 OFF.
EX. FAN1 ON = 70°C and FAN1 OFF = 60°C FAN INT. ACTIVATION = 65°C
Before enabling the function, check that the connection of the two ventilation bars is distributed in such a way that the RH
bar is connected to the FAN2 relay, pins 1-2, and the LH bar is connected to FAN1, pins 3-4.
By selecting FAN1 "NO OR YES", the function will be disabled.
Note: once the FAN1 threshold is exceeded, the control unit will activate both bars.
To enable the INTELLIFAN function, read the programming section on pages 14-15.
Note: for correctly working of the INTELLIFAN function we recommend you observe ΔT 10°C between FAN1 ON
and FAN1 OFF. The connection with the devices of the VRT series must have Intellifan function disabling, the
FAN1 contact must be directly connect to the enable contact of the VRT.
Also connects with the devices of the VRT series provide Intellifan disabling function, the FAN1 contact must be
directly connected to the enable contact of the VRT .
Also connects with the devices of the VRT series provide Intellifan disabling function, the FAN1 contact must be
directly connected to the enable contact of the VRT .
IMPORTANT WARNING
Before carrying out the isolation test of the electrical panel the control unit is installed on, disconnect it together
with the sensors from the power supply to prevent it from being seriously damaged.

19
NT935
SERIES
RS485 MODBUS OUTPUT
INTRODUCTION TO THE MODBUS INSIDE MODULE
The MODBUS INSIDE expansion module is built in the monitoring unit and allows data transfer on a RS485 line with
MODBUS RTU protocol, maximum 32 devices.
OPERATING NOTES
For the module to work correctly, it is necessary to set the RS485 network set-up parameters: address, baud rate, parity
bit. See programming steps 37 to 42 on page 15.
The serial communication of the temperature control monitoring unit is active only when the NT935 AD is in temperature
control mode in one of the intended modes (Scan, Auto, Man and T.Max).
When other functions such as programming, programming display and relay test are activated, the ModBus
communication is temporarily deactivated.
DATA TRANSMISSION ON MODBUS NETWORK
The MODBUS INSIDE internal module allows connecting the NT935 control unit to an RS485 network with Modbus RTU
protocol in order to read the data shown in the MODBUS table on page 21 and write those in the notes for remote
programming; the module is always in slave mode.
The NT935 AD control unit is in communication with the network only when it is in temperature reading mode, while it is
inactive when in the following modes: display, programming and relay test.
RS485 ELECTRICAL CONNECTIONS
As far as the signal cable to be used in order to ensure the correct network operation is concerned, we recommend you
follow the provisions of the EIA RS485 standard which suggests using a 24AWG twisted pair.
The twisted pair that connects units in RS485 might need a 120 ohm end resistor on the last unit of the series.
Connect the twisted pair paying attention to polarities and lay the network avoiding to make sharp bends or ring windings
in order not to modify line impedance. If necessary, the GND terminal for grounding is also available.
Always position the RS485 twisted pair far from power cables.
DATA FRAME
The frame in asynchronous transmission consists of: 1 start bit, 8 data bits, 1 parity bit (even or odd, if the parity has been
set) and 1 stop bit.
With selection parity (none) you can select N-1 (1 stop bit) or N-2 (2 stop bits).
Admitted baud rates are: 2400, 4800, 9600, 19200 and 38400.
If not otherwise specified, the word length (DATA) is 16 bits.
DATA PACKET
A complete sequence of request/answer consists of the following:
Master request:
SLAVE ADDRESS - 1 byte
FUNCTION CODE - 1 byte
DATA - variable, it depends on the function code
CRC - 2 bytes
Slave answer:
SLAVE ADDRESS - 1 byte
FUNCTION CODE - 1 byte
DATA - variable, it depends on the function code
CRC - 2 bytes
1MN0095 REV.
0
(ONLY FOR NT935 AD)

20
NT935
ASERIES
FUNCTION CODE
The ModBus module supports the following function codes:
3(10):- holding register reading
16(10):- register multiple writing
If ModBus receives a message and a CRC error is detected, no answer is given.
CODE 3(10).
Request:
Slave address, code 3(10), Starting address HI, Starting address LO, Number of Point HI, Number of Point LO, Crc LO, Crc HI.
Answer:
Slave address, code 3(10), Byte count, Data HI, Data LO……., Crc LO, Crc HI.
CODE 16(10).
Request:
Slave address, code 16(10), Starting address HI, Starting address LO, Number of Point HI, Number of Point LO, Byte count,
Data HI, Data LO……., Crc LO, Crc HI.
Answer:
Slave address, code 16(10), Starting address HI, Starting address LO, Number of Register HI, Number of register LO, Crc LO,
Crc HI.
NOTES FOR REMOTE PROGRAMMING
The writeable registers are shown in the MODBUS MAPPING TABLE as W or RW (write or read/write) max number of
registers 72, see table page. 20.
Channels 1÷3 are not disabled; in case of incorrect setting, they are always forced as enabled channels.
If the channel 4 is not enabled and/or the information is not provided for, the following answers are given:
1. Measured temperatures = 0000 (0°C)
2. Temperature AL./TRIP = Value written in E2PROM
3. Channel state = 0000
4. Channel setting = %00000000; %xxxxxxx0 (x=n.d.)
Also in remote programming via ModBus you must take into consideration that the Alarm thresholds must be lower than the
Trip thresholds and that the Fan-on thresholds must be higher than the Fan-off thresholds.
If you try to set these thresholds wrongly, the NT935 monitoring unit won’t proceed with programming and data storage;
therefore in the following readings you will read the data relevant to the previous programming.
After sending a writing request, the monitoring unit will require approximately 1’’ to store the data in eeprom; during the
storage phase, the ModBus module will not be able to process other requests.
If the programming request is successful, the control unit automatically resets and loads the newly set values.
If the information is sent to 4.20mA output = Ch_4 and it is disabled it is forced mode " HOT" ; the same policy applies to
programming from panel.
The "RELAYS STATUS" information indicates the state of excitation of the coils of the relays, so it will be subject to the
"FAIL SAFE" commands.
If writing information is sent towards a READ-only register, the data will be binned without affecting the message received.
At the end of the Write command, data compatibility is checked:
1. in case of incompatibility, the answer is an "exception" and the data packet is refused in full. The code of the
first wrong datum can be requested reading the "Datum error received" register. (NB: this code is lost during
RESET, switching on or data writing in E2PROM);
2. if the data are correct, they are transferred into the non-volatile memory (E2PROM), historical data are
cancelled (Tmax=0°C) and, then, a system RESET is forced.
3. If the WRITE command entails only writing "COMMANDS", it will be performed autonomously and without a
RESET, that is without affecting the control unit data.
This manual suits for next models
2
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