AGM300 MODBUS RTU Operation

Overview

The AGM300 and ADM800 are equipped to communicate with other equipment using the MODBUS RTU protocol. Using this communication channel a MODBUS master device may communicate with up to 15 AGM300s on a communications network, exchanging measurement information, alarm data, fault data, history (logs and trends) and setup information. Additionally, the MODBUS master can control the operating state of an AGM300, placing the AGM300 in any of its different operating modes. The network may be configured such that the AGM300s are connected directly to the MODBUS master device, or the MODBUS master device may communicate with the AGM300s through the ADM800.

(NOTE: This document will assume that the reader is familiar with the various parameters used to set up the AGM300, as well as the different operational modes that the AGM300 may be placed in. If you are unfamiliar with this information, please reference the AGM300 operations manual.)

Protocol Details

A 2 wire RS-485 bus is used for transmission, therefore communication occurs in a Half-Duplex mode. The AGM300 is a slave device and will respond to queries in the MODBUS RTU format from a master device.

Two MODBUS functions are supported. They are function 03 (read holding register) and function 16 (Preset Multiple registers). Please refer to the MODBUS Protocol Reference Guide (available at www.modicon.com/techpubs/techPubNew/PI_MBUS_300.pdf) for protocol detail and use instructions.

Using the two MODBUS functions, a master device may read, modify and write data and status information to any AGM on the network. AGM data is organized into structures (internal to the AGM300) which can be accessed by the MODBUS registers defined in this document. A corresponding set of data structures should be maintained by the master device. These master device data structures become the destination for responses to read queries and sources for preset register commands. When a read holding register query is made by the master device the AGM300 responds by sending the contents of the structure referenced by the specified register. After the master validates the AGM300 response using the CRC bytes, it must then move the data into its matching data structure before individual items may be accessed or modified. Therefore, the master data structure should correspond to the AGM300 data structure byte for byte. Note that some data structures have been divided into multiple registers due to MODBUS RTU message length constrains. To change a setting in the AGM300, the master device first reads the register structure that contains the data item to be modified, makes the desired change, then sends the structure back using the preset multiple register function. If the transaction is successful, the AGM300 sends the appropriate MODBUS response. It is the responsibility of the master device when making modifications to insure that all parameters trasfered fall inside the working limits of the AGM300.

Notes on AGM300 Polling

After the AGM300s are setup and operating, the master device need only poll each AGM for its status register which contains summary data of the AGM’s alarms, faults, and operating state. If exceptions are detected through the status register and more details are required, additional registers can be examined. Also if current PPM values are required, the PPM register provides access to current PPM values for all zones. The AGM300 requires a minimum of 20 seconds to complete a gas concentration measurement for a single zone. Therefore, it is not necessary to poll the AGM300 more frequently than once every 15-20 seconds, as there will not be any new data available/obtained by more frequent polling. In fact, excessive polling will slow the operation of the AGM300. Under no circumstances should the AGM300 be continuously polled at rate faster than 500mS, as this could result in erroneous readings by the AGM300.

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Bacharach ADM800 manual AGM300 Modbus RTU Operation, Protocol Details
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AGM300, ADM800 specifications

The Bacharach ADM 800 and AGM 300 are advanced analyzers designed for efficient monitoring and detection of gases in various applications. Known for their reliability and accuracy, these instruments cater to commercial and industrial sectors, ensuring safety and compliance with environmental regulations.

The Bacharach ADM 800 is a portable gas detection device renowned for its ability to detect multiple refrigerants. With a user-friendly interface, it features a high-resolution display that provides real-time data on refrigerant concentrations, allowing technicians to quickly identify leaks during maintenance operations. One of its standout technologies is a highly sensitive thermal conductivity sensor, which enables the ADM 800 to differentiate between various hydrocarbon refrigerants with precision.

Equipped with data logging capabilities, the ADM 800 can store and retrieve measurement data, making it an invaluable tool for tracking refrigerant trends over time. The device supports USB connectivity for easy transfer of data to computers, facilitating detailed reporting and analysis. Its robust design incorporates a protective casing that ensures durability in challenging work environments, making it ideal for both field use and stationary applications.

On the other hand, the Bacharach AGM 300 is specifically crafted for continuous gas monitoring in HVAC systems. This stationary device excels in measuring concentrations of gases such as CO, CO2, and various refrigerants, ensuring optimal performance and compliance. The AGM 300 uses advanced electrochemical sensors for precise gas measurements, providing real-time feedback and alerting users to any hazardous conditions.

One of the notable features of the AGM 300 is its ability to integrate seamlessly with building management systems, enabling centralized control and monitoring of gas levels across multiple locations. This connectivity enhances the safety of industrial and commercial spaces by allowing for automated responses to detected gas levels, which can significantly mitigate risks associated with gas leaks.

Both models emphasize user-centric design, with intuitive interfaces and clear displays, making them accessible even to those with minimal training. Additionally, their low maintenance requirements and long sensor life contribute to reduced operational costs.

In conclusion, the Bacharach ADM 800 and AGM 300 are exemplary solutions for gas detection and monitoring. Their advanced technologies, robust features, and user-friendly designs make them indispensable for ensuring safety and regulatory compliance in various environments.
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