Nortec Modbus User Manual download pdf (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

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Nortec Modbus User Manual Page 5

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