Legacy register map compatibility layer for industrial grade instruments

The Modbus interface of SR300-D1, SR200-D1, and SR100-D1 industrial-grade pyranometers differs from that of the SR30-M2-D1, SR20-D2, and SR15-D1 legacy instruments. For customers that are not yet able to adopt the Modbus interface of the latest industrial-grade pyranometers, Hukx offers a compatibility layer that allows the industrial-grade instruments to imitate the Modbus interface of legacy instruments. You can use the Hukx Sensor Manager to change instrument behavior. This application note describes how the compatibility layer can be used and what the limitations of the compatibility layer are. 

Introduction

The latest SR300-D1, SR200-D1, and SR100-D1 industrial-grade pyranometers offer many improvements over their legacy counterparts (SR30-M2-D1, SR20-D2, and SR15-D1) in terms of robustness and interfacing, while offering comparable performance as a measurement instrument. 

Improvements to the Modbus interface include the organization of registers in topic-based register groups, the increased use of floating point numbers instead of integers, the introduction of statistics registers, and the introduction of dedicated status indicator registers for internal humidity, leak detection, and instrument tilt. 

Although the Modbus interface of the industrial-grade instruments offers many advantages over the Modbus interface of the legacy instruments, it is not always easy to update the software of existing SCADA systems, and it is sometimes difficult to adopt the new Modbus interface of the industrial-grade pyranometers. 

The two most significant differences in the Modbus interface between the legacy instruments and the industrial-grade instruments are the following:

1. The datatypes are typically different. E.g. in SR30-M2-D1 the irradiance was stored as a 32-bit signed integer. The irradiance was expressed in W/m² divided by a scaling factor stored in another register. In SR300-D1 the irradiance in W/m² is stored as a 32-bit float, removing the need for a scaling factor and corresponding scaling of the data by the SCADA system.

    

2. The registers are located at different register addresses. E.g. in SR30-M2-D1 the irradiance register was located at 0x0002, whereas in SR300-D1 the irradiance register is located at register 0x0200.

For those customers that are not yet able to adopt the interface, Hukx has implemented a compatibility layer that allows the industrial-grade instruments to be used with the Modbus interface of the legacy instruments. After configuring the industrial-grade instrument, users are able to access a Modbus interface that is to a very large extent compatible with the legacy instruments.

This document describes how the compatibility layer can be used and what the limitations of the compatibility layer are. 

Compatibility layer

The compatibility layer allows industrial-grade instruments to imitate the Modbus interface of the legacy instruments. The compatibility layer consists of several parts:

• Registers with the same datatype as in the legacy instruments. For example, SR300-D1 offers the irradiance both as a floating point datatype and as a legacy signed 32-bit integer datatype. A list of registers with the register address on legacy instruments and the register address on industrial- grade instruments is shown in Table 2. 

   

• Registers can be mapped to another register address. Internally, the instrument will map an alias register address to a default register address. When configured, this allows registers to be accessed at the same address as in the legacy instruments. 

  For example, in SR30-M2-D1 the irradiance could be read as a 32-bit signed integer at register address 0x0002. On SR300-D1 by default the same register is available at register address 0x0270. However, when the SR30-M2-D1 legacy register map is enabled on SR300-D1, Modbus client can instead read address 0x0002. Internally, the device will map the alias register address 0x0002 to the default register address 0x0270 and the register at 0x0270 is read instead. 

The Hukx Sensor Manager can be used to program the register address map and to enable or disable the  register address mapping feature. 

• For SR300-D1 Modbus coils for controlling the heating and ventilation are available at the same coil address as in SR30-M2-D1.

The compatibility layer is available from a certain firmware version onwards. The firmware version of your instrument can be checked using the Hukx Sensor Manager (HSM). Table 1 lists the minimum firmware version of the industrial-grade pyranometers that support the compatibility features.