User Manual

E-M-HF4-V1_22

Rotronic AG

Bassersdorf, Switzerland

Document code

Unit

HygroFlex HF4 Humidity Temperature

Transmitters: User Guide

Instruction Manual

Document Type

Page

7 of 29

Document title

3.5 Digital interface (HF45)

a) RS-485 serial interface

The HF45 has always a RS-485 serial interface. When the number of available network ports is limited, this

interface can be used to connect together up to 64 devices in a multi-dropped arrangement. In principle, an

unlimited number of such networks can be monitored with the HW4 software, but each RS-485 multi-drop

network is limited to 64 devices. The HF45 can be used either as a slave or a master, without special

configuration. The master is automatically the device that is directly connected to a network (PC or LAN) by

means of a USB port or TCP/IP port.

RS-485 Compatibility: The communication protocol used by the HF45 and other AirChip 3000 products is not

compatible with the protocol used by the previous generation of ROTRONIC instruments. Do not connect

legacy products and AirChip 3000 products to the same RS-485 multi-drop network.

b) USB or Ethernet interface

The HF45 is also available with the following interface combinations: USB + RS-485 or Ethernet +RS-485. In

that case the protection grade of the HF4 enclosure is no longer IP65 / NEMA 4 rated.

c) Communication protocol options

The measurement data can be read without having to use the ROTRONIC HW4 software. Starting with

firmware version 1.3, the HF4 offers the following communication protocol options (ASCII) which can be

selected by connecting the HF4 to a PC running the ROTRONIC HW4 software (version 2.1.1 or higher):

o RO-ASCII: this is the standard (default) communication protocol used by all AirChip 3000 devices and by

the HW4 software. In principle, this protocol supports all of the AirChip 3000 functions but some of the

functions require a certain amount of computations to be carried out by an external device such as a PC.

o Custom: this communication protocol can be used to provide compatibility of the HF4 with an existing

communication system. The Custom communication protocol is limited to reading measurement data from

the HF4. Functions such as device configuration, humidity and temperature adjustment, etc. are not

supported. The Custom protocol is applicable to all AirChip 3000 devices with a digital interface and

allows RS-485 networking

o Modbus: the Modbus protocol available with the HF4 is limited to reading measurement data from the

HF4. Functions such as device configuration, humidity and temperature adjustment, etc. are not

supported by the Modbus protocol.

When using either the RO-ASCII or the Custom protocol, the HF4 can be set to send data automatically after

each refresh cycle without requiring a data request. When this mode is enabled, the receiving device must be

listening at all times in order to get the measurement data.

For details, see document E-M-AC3000-CP