Hysteresis Temperature Control

Table of Contents

• Overview
• What is Hysteresis Temperature Control?
• Step 1: Define the Hysteresis Temperature Control Class
• Step 2: JSON Configuration for Inputs, Outputs, and Thresholds
• Step 3: Implement the Hysteresis Control Logic
• Conclusion

Overview

In this tutorial, we will create a control using a hysteresis-based approach to manage temperature. Hysteresis control is often used in systems that need to prevent rapid switching and stabilize a control variable around a set point. We will configure this control to activate or deactivate an output based on fixed temperature thresholds, creating a stable temperature range.

The objectives of this tutorial are to:

• Explain the concept of hysteresis control.
• Define the control class for basic hysteresis temperature management.
• Implement the hysteresis logic to control an output based on fixed temperature thresholds.

What is Hysteresis Temperature Control?

Hysteresis control is a method of managing a system output based on an upper and lower threshold. In temperature control, hysteresis helps maintain a target temperature range without frequent on-off cycles, which can lead to instability and wear on equipment.

For example, in a heating system, the heater may turn on when the temperature drops below a lower threshold and turn off when the temperature exceeds an upper threshold. The gap between the two thresholds prevents the system from rapidly switching, allowing the temperature to fluctuate within a stable range.

Step 1: Define the Hysteresis Temperature Control Class

In this control class, we will define one xentara::Float64Input for the temperature input and one xentara::BooleanOutput for the heater state output. We will also include fixed configuration parameters for the upper and lower thresholds.

Here is the code for SimpleHysteresisTempControl.hpp:

#pragma once
 
#include <xentara/cpp-control.h>
 
class SimpleHysteresisTempControl final : public xentara::Control
{
public:
    void initialize(xentara::InitContext &context) override;
 
    void step(xentara::RunContext &context) override;
 
private:
    /// Xentara-managed input data point for temperature
    xentara::Float64Input temperatureInput;
 
    /// Xentara-managed output data point for heater state
    xentara::BooleanOutput heaterState;
 
    /// Configured lower and upper temperature thresholds
    double lowerThreshold {0.0};
    double upperThreshold {0.0};
};

Step 2: JSON Configuration for Inputs, Outputs, and Thresholds

The following JSON configuration file sets up the data points for the temperature input and heater state output, as well as the parameters for the lower and upper thresholds.

{
  "children": [
    {
      "@Skill.CPP.Control": {
        "name": "Simple Hysteresis Temperature Control",
        "UUID": "bbbe9b21-602e-4ac7-bd7a-e09d80cf0957",
        "controlPath": "libsimple-hysteresis-temperature-control.so",
        "parameters": {
          "lowerThreshold": 18.0,
          "upperThreshold": 22.0,
          "temperatureInput": "Temperature Input",
          "heaterState": "Heater State"
        }
      }
    },
    {
      "@Skill.SignalFlow.Register": {
        "name": "Temperature Input",
        "UUID": "c2e17c47-90ab-4aac-a24d-98e9d6ed80df",
        "defaultValue": [ "float64", 20.0 ]
      }
    },
    {
      "@Skill.SignalFlow.Register": {
        "name": "Heater State",
        "UUID": "fd032506-6db5-4cc6-a8e5-c9b3229ef158",
        "defaultValue": [ "bool", false ]
      }
    },
    {
      "@Track": {
        "name": "Control Track",
        "UUID": "fb0a26f8-7d84-4af9-9345-4145263d09c7",
        "children": [
          {
            "@Timer": {
              "name": "Timer",
              "UUID": "e6580c24-dbf9-43a0-aa81-c5ed8da6f734",
              "period": "50ms"
            }
          },
          {
            "@Pipeline": {
              "name": "Pipeline",
              "UUID": "040f156e-2744-4008-8195-cd7f17078668",
              "triggers": [
                "Control Track.Timer.expired"
              ],
              "checkpoints": [
                {},
                {}
              ],
              "segments": [
                {
                  "start": 0,
                  "end": 1,
                  "tasks": [
                    {
                      "function": "Simple Hysteresis Temperature Control.step"
                    }
                  ]
                }
              ]
            }
          }
        ]
      }
    }
  ]
}

In this configuration:

• Temperature Input is the input data point representing the current temperature.
• Heater State is the output data point indicating the heater on/off status.
• The control parameters include lowerThreshold and upperThreshold to specify the temperature range.

Note

In this example, the @Skill.SignalFlow.Register skill is used for simplicity. However, other skills should be used to connect to the sensors depending on the specific hardware and protocols in use. For instance, skills such as EtherCAT, Modbus, or OPC UA could be used to interact with real-world temperature sensors. The choice of skill depends on the communication protocol supported by the device.

Step 3: Implement the Hysteresis Control Logic

In SimpleHysteresisTempControl.cpp, we will initialize the input and output data points and configure the hysteresis thresholds in the initialize method. The step function will check the temperature against the thresholds and turn the heater on or off accordingly.

Here is the code for SimpleHysteresisTempControl.cpp:

#include "SimpleHysteresisTempControl.hpp"
 
/// Registers the SimpleHysteresisTempControl with Xentara.
const xentara::ControlExporter<SimpleHysteresisTempControl> kSimpleHysteresisTempControl;
 
void SimpleHysteresisTempControl::initialize(xentara::InitContext &context)
{
    // Initialize the temperature input and heater state output
    temperatureInput = context.config().getDataPoint("temperatureInput");
    heaterState = context.config().getDataPoint("heaterState");
 
    // Retrieve configured thresholds
    lowerThreshold = context.config().getDouble("lowerThreshold");
    upperThreshold = context.config().getDouble("upperThreshold");
}
 
void SimpleHysteresisTempControl::step(xentara::RunContext &context)
{
    // Read the current temperature
    auto currentTemperature = temperatureInput.read(context);
 
    // Apply hysteresis control based on fixed thresholds
    if (currentTemperature < lowerThreshold)
    {
        // Turn heater on
        heaterState.write(context, true); 
    }
    else if (currentTemperature > upperThreshold)
    {
        // Turn heater off
        heaterState.write(context, false);
    }
    else
    {
        // do nothing
    }
}

Conclusion

In this tutorial, we implemented a basic hysteresis temperature control. This control reads a temperature input and, based on fixed thresholds, turns a heater on or off to maintain a stable temperature range. This setup provides a simple yet effective method to stabilize temperature in systems requiring consistent management within defined limits.