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Polling

Polling

Evolution of Polling

Polling in industrial communication protocols refers to the systematic polling of devices or sensors over a network at regular intervals to collect data efficiently. In this process, a central controller polls each device in turn to determine if it has data to report. The central server collects the responses and processes the collected data at regular intervals. Although polling is resource intensive and can lead to higher latency, it is valued for its simplicity and control over data collection in industrial applications. 

By the 1950s, advancements in automation and early computerized systems began to permeate various industries. These technological strides necessitated improved methods for sequentially querying multiple devices or sensors—which gave way to polling. This period saw a growing sophistication in the application of polling techniques to streamline data collection and command dissemination. Throughout the 1960s and 1970s, the development of early computer networks, including ARPANET and Ethernet, refined these polling techniques. Such innovations were crucial in enhancing industrial control systems by facilitating efficient data collection from sensors and control of actuators. This era witnessed significant progress in how polling methods were adapted for industrial use within these nascent networks. 

The widespread adoption of digital communication protocols, such as MODBUS and PROFIBUS during the 1980s and 1990s, further propelled the evolution of polling methods. These protocols were integral to industrial automation, as they encapsulated polling techniques, which became fundamental for real-time data retrieval from remote devices within industrial settings. This period marked a consolidation of polling as a cornerstone method in industrial communication systems. Entering the 2000s, the rise of Internet connectivity and the advent of the Industrial Internet of Things (IIoT) marked another transformative phase for polling techniques. These methods adapted to accommodate distributed and interconnected systems, making polling over IP networks commonplace. 

This evolution empowered remote monitoring and control of industrial equipment, significantly enhancing operational efficiency and data integrity. In the 2010s and into the present day, polling techniques have continued to evolve, leveraging state-of-the-art communication technologies such as MQTT, OPC UA, and wireless protocols like Zigbee and LoRaWAN These advancements have facilitated real-time polling over wireless networks, providing greater flexibility and scalability in industrial communication systems. The integration of IIoT technologies has been particularly impactful, enabling seamless capture and transmission of real-time data between smart devices and machines, thus optimizing automation and self-optimization processes 

Polling methods have thus journeyed to becoming integral components of modern industrial communication infrastructures. Today's advanced polling techniques enhance the capabilities of IIoT by enabling real-time data exchange and analytics crucial for modern industrial optimization and operational efficiency. 

Polling Mechanism

Polling in industrial communication refers to the systematic querying of devices or controllers within a network to manage communication and exchange information and control signals. The framework is based on master-slave model and follows a structured approach: 

  • Network Initialization

    The master device establishes the communication network, and all slave devices are identified and assigned unique addresses or IDs. 

  • Polling Schedule Configuration

    The master configures the polling schedule, determining the order and frequency of polling each slave. This schedule can be static or dynamically adjusted based on operational needs. 

  • Master Device Sends Polling Reques

    The master sends a request to the first slave device in its schedule, typically including the slave's address and a command to read data or check status. 

  • Slave Device Responds

    The slave device processes the request and responds with relevant data, such as sensor readings, operational status, or acknowledgement of an action. 

  • Master Device Processes Response

    The master processes the data received from the slave. Actions based on this data could include updating control processes or logging the information. 

  • Move to Next Slave

    Once the current slave's response is processed, the master moves to the next slave in the schedule, repeating the polling process. 

  • Cycle Repeats

    The master continues polling according to the predetermined schedule. After all slaves are polled, the cycle restarts. 

  • Error Handling

    If a slave does not respond or an error occurs, the master may log the error, retry the request, or move on to the next slave depending on the protocol's error-handling strategy. 

  • Data Exchange Confirmation

    Some systems require confirmation that data has been successfully exchanged, either through acknowledgment from the master or the slave's confirmation of command execution. 

  • End of Polling Cycle

    The polling cycle generally continues indefinitely for continuous monitoring and control, unless the master receives a command to stop. 

Polling Variants in Industrial Communication

  • Time-Based Polling (Periodic Polling) is a common method wherein a controller queries each device on the network at regular, fixed intervals, regardless of the device's immediate state or the urgency of its data. This makes sure that each device has an equal opportunity to communicate, but it might lead to inefficiencies if the device data changes infrequently. 
  • Token-Based Polling (Token Passing) involves a token—a special data packet—that is circulated among the devices in the network. Only the device holding the token is allowed to communicate with the controller. This method ensures orderly and predictable communication, as the token passing follows a pre-defined sequence. Token passing contrasts polling access methods by eliminating a predetermined master node, thus preventing data collisions and ensuring orderly network communication. 
  • Priority-Based Polling assigns different priority levels to devices based on their importance or the urgency of their data. Higher-priority devices are polled more frequently or immediately, when necessary, whereas the lower-priority devices are polled less frequently or when system resources allow. Priority-based polling can be pivotal in improving multitask execution and ensuring critical processes receive timely attention. 
  • Selective Polling engages with the selective querying of devices based on specific criteria like device status, operational conditions, or alarms. This method minimizes unnecessary communication by targeting only those devices requiring immediate attention. Selective polling is particularly beneficial in scenarios where certain devices need more frequent interaction while others don't. 
  • Group Polling (Batch Polling) involves the grouping of devices based on functionality or location. The controller sends a single request to the entire group, and all devices within that group respond either sequentially or simultaneously. This technique simplifies communication and can increase efficiency, particularly in environments where multiple devices perform similar functions and need coordinated operation. 
  • Event-Driven Polling is triggered by specific events or changes in device status rather than occurring at fixed intervals. Devices alert the controller when they have significant data to report, often using interrupts or status flags, thus ensuring prompt responses to critical changes]. 
  • Asynchronous Polling operates dynamically without a fixed sequence or interval. Instead, the controller decides in real-time when and which devices to poll based on current conditions. This flexibility allows for adaptive communication that can efficiently handle unpredictable and varying operational requirements. 
  • Demand-Driven Polling initiates polling based on specific requests or operational demands. The controller polls devices in response to user inputs, process states, or external conditions to ensure that the polling activity closely aligns with immediate operational needs.

Advantages of Polling

The advantages of polling in industrial communication encapsulate several characteristics: 

Deterministic Communication Patterns

Polling ensures predictable and consistent communication patterns as the system checks for data at regular intervals. 

Controlled Bandwidth

In a polling system, the master device governs the frequency of data exchange, which aids in efficient bandwidth management. 

Simplicity

Polling is straightforward to implement and comprehend, often favored for its ease of execution. 

Addressable Communication: This method allows the master device to directly address each slave device, ensuring each device can be uniquely queried. 

Error Handling

Polling can efficiently manage error detection and recovery, as it can be programmed to recheck devices or channels where issues are identified. 

Real-Time Monitoring

One prominent benefit of polling is its ability to provide continuous real-time monitoring of sensor data and system status. 

Compatibility

Polling operates effectively across various network topologies, including star, bus, and ring structures. 

Efficiency

It optimizes the data transfer process by systematically accessing each device in a pre-determined manner, which ensures no device is overlooked. 

Scalability

Polling can accommodate an increasing number of devices while maintaining the integrity and sequence of communication. 

Customizability

The polling schedules can be tailored to meet specific system requirements and priorities, allowing for more flexible and adaptive communication systems. 

Industrial Communication with Hilscher

As a leading company in the field of industrial communication, Hilscher offers a broad portfolio of technologies and solutions for networking industrial environments. 

This includes a wide range of interface solutions for connecting sensors, actuators and controllers to industrial communication networks. The communication controllers of the netX family form the basis for this. The multi-protocol-capable SoCs can be integrated into automation components as required and their extensive chip peripherals enable powerful, efficient and flexible solutions. A protocol change is achieved by simply reloading Hilscher's own netX firmware. Building on this, the company also offers embedded modules and PC cards in all form factors in order to realise the netX communication interface with less integration effort. 

Hilscher also offers a comprehensive managed industrial IoT range under the netFIELD brand. This ranges from edge gateways as an application-oriented computer platform with integrated container management and the Edge OS Runtime running on it to the central cloud portal, via which the docker containers are deployed to the edge devices, through to turnkey containers for communication applications. 

Gateways and switches, devices for network diagnostics as well as masters and bridges for the wireless connection of IO-Link sensors round off the automation portfolio. 

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