Nortec Modbus - Manual (Page 5)

Introduction
Many Nortec humidifiers feature control boards that include Modbus RTU and can connect to
Modbus networks right out of the box. This document describes how to connect these
humidifiers to such a network and defines the parameters that may be monitored.
Please note that there are differences between Modbus RTU and Modbus TCP. Nortec
humidifiers are Modbus RTU capable and require a gateway (by others) for Modbus TCP
networks. Contact the factory for more information on Modbus TCP communications.
Requirements
NH-EL Humidifiers are capable of Modbus RTU and require no additional hardware for this
connection.
Nortec humidifiers that feature that Total Controller (“TC”) control boards are also capable of
Modbus RTU. These include the NHTC, the GSTC, SETC, and MHTC humidifiers.
Additionally, the RH2 and MES-2 models feature a digital control board that supports Modbus,
however these models require an adapter board to provide the Modbus interface. Finally, the
NHRS also supports Modbus communications; however a TTL converter is required for this
functionality. Refer to following table for more information, items described as “optional” are
for convenience (but not required for Modbus), while items listed as required are needed for
Modbus functionality:
Table 1: Modbus Accessories
Part
Number
Kit Name Kit Description
2553787 NHTC, GSTC, SETC Modbus Connection Optional adapter cable for NHTC, GSTC, SETC.
2560630 MHTC Modbus Interface
Optional terminal block for MHTC Modbus interface.
2531585 Modbus Option for OEM Digital Board
Required adapter board and terminals for Modbus
connections.
2560631 NHRS Modbus converter
Required TTL converter for NHRS Modbus
connections.
Please consult your local Nortec representative to orders connection kits.
Wiring Connections
Using the correct wiring between the humidifier and the Modbus network is important to ensure
reliable communications and reduce the impact of electrical interference. The recommended
wire type is 18 -24 AWG, shielded twisted pair wire with 120 Ohm characteristic impedance. As
an alternative, CAT-5 (“Ethernet”) cable exceeds these specifications and may be used. In this
case, only two of the conductors and the wire shield will be used; care must be taken to isolate
any unused conductors.
Regardless of which wire type is used ensuring the correct shield terminations is necessary to
prevent electrical interference. The wire shield should be terminated at either the humidifier or
the Modbus system, but not both. This allows induced current to “drain”; if the shield is
terminated at both ends it will function as a conductor and can actually increase electrical
interference. To minimize signal loss a wire run should not exceed 2000 feet. Additionally, to
ensure communication reliability, it is recommended that no more than 8 humidifiers are
2 |Modbus Installation