18
NT935BH
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 13-14.
IMPORTANT INFORMATION
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.
OUTPUT RS485 MODBUS
INTRODUCTION TO THE MODBUS INSIDE MODULE
The MODBUS INSIDE expansion module is incorporated within the monitoring unit and allows data transfer on a RS485
line with MODBUS RTU protocol, maximum 32 devices.
OPERATING NOTES
For correct functioning of the module it is necessary to set the RS485 network set-up parameters: address, baud rate,
parity bit.See programming steps 36 to 41 on page 11.
The serial communication of the temperature control monitoring unit is only active when the NT935BH-D 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 makes it possible to connect the NT935BH-D control unit to an RS485 network
with Modbus RTU protocol in order to be able to read the data indicated in the Modbus table, page 21, and to be able to
write the data indicated in the paragraph notes for remote programming. The module is always in slave mode.
The NT935 RS485 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 test relays.
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 NO parity (none) it is possible to select N-1 (1 stop bit) or N-2 (2 stop bit).
The permitted baud rates are: 2400, 4800, 9600, 19200 and 38400.
If not otherwise specified, the word length (DATA) is 16 bits.
1MN0095 REV. 0
