Tank Thermoregulation with Portenta Machine Control & Opta™

Introduction

In this application note, you will learn how to control the temperature of an industrial tank using a PT100 RTD sensor connected to a Portenta Machine Control and an Opta™ that will be responsible for the tank temperature control.

The system will send the temperature values from the Portenta Machine Control to the Opta™ using Modbus RTU over the RS-485 interface. The Opta™ will subsequently use these values and control the reservoir temperature accordingly.

Goals

• Establish connection between Portenta Machine Control and Opta™ using Modbus RTU
• Control the temperature of a tank of industrial category
• Learn about Modbus RTU and RS-485 of how it can be used in different professional applications
• Learn more about PLC IDE and how to use it to create Modbus communications in industrial environments

Hardware and Software Requirements

Hardware Requirements

• Portenta Machine Control (x1) Opta™ PLC with RS-485 support: Opta™ RS485, or Opta™ WiFi (x1)
• Micro-USB cable (x1)
• USB-C® cable (x1)
• PT100 RTD (x1)

Software Requirements

• The Arduino PLC IDE
• Portenta Machine Control - PLC IDE Activation
• Opta™ - Set up with PLC IDE
• You can directly download the Arduino PLC IDE Projects and extract them in your workspace

It is recommended to read "Connect RTD/Thermocouple to the Portenta Machine Control" tutorial before continuing to follow the present tutorial.

Temperature Sensor

In this tutorial, a Two-wire PT100 RTD is used, but you can also use a Three-wire RTD or a thermocouple depending on your requirements or preferences. You can learn more about the differences between these temperature sensors and how to connect them to the Portenta Machine Control following the previously mentioned tutorial. It is recommended to read this tutorial to learn the basics about the temperature sensors introduced earlier.

Connections

To establish communication between Opta™ and the Portenta Machine Control, we will do it through Modbus RTU communication using the RS-485 interface. The following table shows the required connection between two devices to achieve this communication:

The Portenta Machine Control has support for full-duplex communication, while Opta™ specifically supports half-duplex communication. Due to this reason, the TXP and TXN RS-485 pins will be used only on the PMC as shown in the following image:

Because Opta™ has no internal termination resistors, it must be installed per the Modbus protocol specification adding termination resistors. Also, if you experience inconsistent data transmission using Opta™ with other Modbus RTU compatible devices, please try again by inverting the A(-) and B(+) lines.

PLC IDE

To enable this example, you will need to create two PLC IDE projects. One project will be for the Portenta Machine Control, which will act as a Server in the Modbus RTU communication, while the other project will set the Opta™ to behave as the Client.

To create a project, open PLC IDE and click on

New Project

Portenta Machine Control Project

Create the PMC Project

After clicking on

New Project

Portenta Machine Control 1.0

Modbus Server Configuration

Once created, you will configure the Modbus RTU connection through the RS-485 serial port. To do this, go to the resources window and double-click on

RS485 SerialPort

Resources

View > Tool windows > Resources

On the

Modbus Configuration

• Mode: Modbus RTU Slave
• Port Type:

  RS485

• Baud rate: 19200 b/s
• Serial Mode: N,8,2 (No parity, 8 data bits, 2 stop bits)
• Modbus address: 17

In this case, Modbus Server address is set as 17, but you can define one address in the

1 ... 247

Do not forget the configured Modbus address, as you will need it in the future.

You will now create the variable that will be sent through Modbus RTU. To do this, go to the

Resources

Status variables

A

Status Variables (volatile)

Add

• Address: 25000
• Name: temp_send
• PLC type: INT

If everything is correct, it should look like in the next image:

This is all the necessary configuration on the server side. In the next step, you will configure the temperature sensor to be paired with Portenta Machine Control.

Temperature Sensor Configuration

We need to read the values of the temperature sensor. In this case, we are using a PT100 RTD as explained in the Connect RTD/Thermocouple to the Portenta Machine Control tutorial, but you can also use a Three-wire RTD or a Thermocouple depending on what you need.

To configure the temperature sensor, in the

Resources

Temperature probes

Behavior setting

TPXX

In this case, we are using an

RTD TWO WIRES

TP00

Inside the

Project

Main

Tasks

Fast

Local variables

Insert

Ctrl + Shift + Ins

temp0

Real

Main Program Code

In the code section, you have to write the following code:

Copy
1temp0 := sysTempProbes[0].temperature;
2temp_send := temp0 * 100.00;

The Main code will read the sensor values from the temperature sensor stored in

sysTempProbes[0]

By default, the project creates an automatic type int global variable called

cnt

Delete

Monitor the Values

Once followed all the previous steps, you will need to compile the program and download it to the Portenta Machine Control. First, connect your device and click on the

Connect to the target

On-line > Connect

Once connected, click on the

Compile PLC Project

Project > Compile

Then click on

Download PLC code

On-line > Download code

To ensure that we are reading correct temperature values on the Portenta Machine Control, you can pick and drop the variable to the

Watch

Watch

View > Tool window > Watch

Opta™ Project

Create the Opta™ Project

After creating and configuring the Portenta Machine Control project, you can create a new project for Opta™ by clicking on

File > New Project

Opta 1.0

Client Modbus Configuration

On the Opta™ side, you will need to configure Modbus as the Client to receive the temperature values. To do that, you need to go to the

Resources

RS485 SerialPort

On the

Modbus Configuration

• Mode: Modbus RTU Master
• Baud rate: 19200 b/s
• Serial Mode: N,8,2 (No parity, 8 data bits, 2 stop bits)

The configuration should contain same setting as the following image:

After configuring the Serial Port, go to the

Resources

RS485 SerialPort

Add

A new window named

Device catalog

Generic Modbus 1.0 Generic Modbus node

Select

On the

Generic Modbus node

Modbus address

Now that we added the Portenta Machine Control Modbus node to the net, we need to read the temperature values from its database. To do this, right-click on the

PMC

Add

Here is a comprehensive list of the different options that you can add depending on your necessities:

• Modbus FC-01 (Read Coils): reading of one or more RW bits by the slave node
• Modbus FC-02 (Read Discrete Inputs): reading of one or more RO bits by the slave node
• Modbus FC-03 (Read Holding Registers): reading of one or more RW registers by the slave node
• Modbus FC-04 (Read Input Registers): reading of one or more RO registers by the slave node
• Modbus FC-05 (Write Single Coil): writing of a single RW bit on slave node
• Modbus FC-06 (Write Single Register): writing of a single RW register on slave node
• Modbus FC-15 (Write Multiple Coils): writing of one or more RW bits on slave node
• Modbus FC-16 (Write Multiple registers): writing of one or more RW registers on slave node

We will select

Modbus FC-04 1.0 Read Input Registers  - Function 04 (0x04)

Select

After clicking on

Select

With the parameters defined, click on the

Input Reg.

add

temp_volt

To select a type for this variable, we need to go to the

Projects

Modbus_Vars

temp_volt

INT

Type

Main Program Code

Before going with the main program code, go to the

Project

Global_vars > New variable > Automatic

temp

REAL

Ok

Now that we have created the global variable where we are going to store the temperature values in

REAL

main

Project

Local variables

Insert

Ctrl + Shift + Ins

threshold

REAL

In the code window, paste the next code:

Copy
1//Set the temperature threshold to trigger on the relay
2
3threshold := 30.00;
4
5//This IF - ELSE turns on the Green LED when the Modbus communication is ok
6
7IF sysMbMRtuNetList[0].active = FALSE THEN
8    LEDG := FALSE;
9ELSE 
10    LEDG := TRUE;
11END_IF;
12
13//Adjust the received temperature data into actual correct value.
14temp := temp_volt / 100.00;
15
16//Control the relays depending on the temperature value compared to the Threshold
17
18IF temp >= threshold THEN
19    relay_1 := TRUE;
20    LED1 := TRUE;
21ELSE
22    relay_1 := FALSE;
23    LED1 := FALSE;
24END_IF;

The main program window should look like this:

The variables

LED1

LEDG

relay_1

• LED1

  : is the number one status LED.

• LEDG

  : represents the Green LED.

• relay_1

  : represents the relay terminal one.

To use the variables

LED1

LEDG

relay_1

1. Navigate to the Resources tab.
2. Proceed to LED Outputs.
3. Associate the

   LED1

   and

   LEDG

   variables with their respective hardware outputs: 'L1' and 'LG'.

The setup should resemble the following image:

Following a similar process:

1. For the

   relay_1

   variable, associate it with the

   O1

   hardware output.
2. This can be done in the 'Relay Outputs' mapping section:

Mapping onboard elements ensures that your software instructions directly influence the corresponding physical hardware components, bridging your program's logic with real-world actions.

Task Configuration

It is recommendable to set an executing period of 50 ms for the main task; to do this, double-click on

Tasks

Project

Tasks Configuration

On this window, change the

Set period

Fast Task

Yes

Monitor the Values

Before begin monitoring the values, connect your Opta™, compile the code, and download it to the board as shown in the Portenta Machine Control Monitor the Values section. The following short clip provides an overview of what you can expect during the operation:

Note:

temp_volt

If you reach the threshold of 30 degrees Celsius, the Opta™ device's relay will close and the LED1 will turn on. Remember that you can set this value to any value you need by changing the threshold parameter in the main program code.

Download the PLC Project

We recommend you follow all the steps to understand thoroughly how the project works and what are we doing in each step, but you can also directly download the Arduino PLC IDE Projects on the Software Requirements section and uncompress the Zip file on your Arduino PLC IDE Projects Folder to set and test the example project.

Conclusion

In this tutorial, you have learned how to measure and control the temperature of an industrial tank by reading the temperature values using an RTD with the Portenta Machine Control and sending it via Modbus RTU on the RS-485 interface to process the reading values and controlling a relay, activating a cooling system when a temperature has reached the threshold.

Next Steps

It has been a theoretical guide on how to do it, so the challenge in this project now is to apply it in a real environment scenario, taking into account some other factors and applying PID, normally used in these industrial applications.

Note that this same circuit can be used for many more scenarios than the temperature control of an industrial tank, as well the heating control of a home, or the refrigeration of a food chamber.

Use your imagination and knowledge to put into practice what you have learned in this tutorial, and if you have any questions, feel free to ask them at our Arduino Help Center.