We will now look at using serial Modbus RTU to communicate to a Solo process temperature controller using our BRX Do-More Controller. Serial communication instructions will allow you to send and receive serial data to an external device. The communication method that you setup can be ASCII or numeric (binary). ASCII (American Standard Communication for Information Interchange) can be used to send to devices such as a printer or display.
Receiving ASCII can be used for connecting barcode scanners to the PLC. The barcode will be read as an ASCII string in the PLC.
The BRX Do-More Series PLC will allow you to use instructions such as STREAMIN and STREAMOUT to send and receive data from devices mentioned above. They are usually a one to one device and do not have a protocol.
A protocol is like a language used to communicate to different devices connected together. Modbus serial communication (Modbus RTU) is a standard protocol used in many industrial automation devices. The BRX Do-More Series PLC has a MRX (Modbus Network Read) and MWX (Modbus Network Write) instructions.
We will demonstrate these instructions by communicating Modbus RTU to a Solo Temperature Controller. (RS485) Our example will read the current process (PV) value and write the set point value (SV) in the controller. Let’s get started. Continue Reading!
The SOLO Temperature Controller is a single loop dual output process temperature controller that can control both heating and cooling simultaneously. It is available in 1/32, 1/16, 1/8, and 1/4 DIN panel sizes and is UL, CUL and CE approved. The name of the temperature controller is deceiving. This unit will also accept voltage and current into them, which is great for process control.
Recently I was asked: How you can change the pressure value from PSI to Bar?
They were bringing into the controller a voltage signal. This can be scaled using the tP-H (High-level signal) and tP-L (Low-level signal). The units on the display scaled for you. The default is -999 to 999. See section 11-2 of the following information guide that comes with the controller. Continue Reading!
The SOLO Temperature Controller is a single loop dual-output process temperature controller that can control both heating and cooling simultaneously. It is available in 1/32, 1/16, 1/8 and 1/4 DIN panel sizes and is UL, CUL and CE approved.
There are four types of control modes: PID (Auto Tuning (AT) function) P stands for proportional and accounts for present values of the error – It reacts to the amount of error which is the difference between the SP (Set Point) and the PV (Present Value) I stands for integral and accounts for past values of the error – It uses math to basically find the approximation of the area under the curve. D stands for derivative and accounts for possible future values of the error, based upon the rate of change – It uses math to determine the slope of the error over time and multiply this by the derivative gain. AT – Auto-Tuning as the name implies will automatically cycle your control system through two cycles and set the PID parameters.
ON / OFF
On/Off control is the simplest form of control. In the case of temperature, the output will be on when the temperature is below-set point. When the temperature gets above the set point of the controller the output will be off. When this cycling occurs frequently, you can add hysteresis to the output. This will limit the time the output goes on and off by a number of degrees.
Manual mode is when you need to control the output directly. By entering manual mode the operator can adjust the values of the output(s).
Ramp / Soak control
The Ramp / Soak control mode is used to control the outputs according to the pre-programmed SP patterns with the PID control method. The Solo can have eight programs with eight steps each. Note: This can be increased with the additional use of hardware and software via HMI or PLC.
The available outputs include relay, voltage pulse, current, and linear voltage. There are up to three alarm outputs available to allow seventeen alarm types in the initial setting mode. SOLO can accept various types of thermocouple, RTD, or analog input. This means that cascade control is possible with these controllers.
When you use the output of one of the Solo process controllers as the input to another, this would be cascade control.
It has a built-in RS-485 interface using Modbus slave (ASCII or RTU) communication protocol.
The Solo Process Temperature Controller can be configured through the buttons on the front of the unit or by the configuration software. Monitoring of up to four controllers at once can be done through the same configuration software.
The following is the wiring of the Modbus Serial communication. We will use a USB to RS485 converter from Automation Direct. (USB-485M)
Installation and operation instructions can be found at the following link: USB to RS485 PC Adapter Installation
The solo process temperature controller needs to be setup before we can communicate to it. The default setting is ‘Off’ for the On-Line Configuration. Here is the way to change into the different modes in the Solo.
In the Initial Setting Mode we will change the online configuration and make the changes to the Modbus settings as follows: 9600 Baud, Even, 7 Data Bits, 1 Stop Bit, Modbus ASCII Format. We will leave the default unit number as 1.
The configuration and monitoring software does not have to be installed. You just need to download the file “slsoft.zip”.
Once downloaded right click on the file and select “Extract All…”. The file ADC1105.exe can now be run.
The recommended screen resolution is 1024 x 768. If you do not have this resolution then there is another program that will allow us to create a shortcut to this program and change our default resolution. After we exit the program, our screen resolution will return to its original state.
Download the exe file (reso.exe) into the same extracted folder that you have the ADC1105.exe file.
Click on the reso.exe file in the folder to run the application.
Click the Browse… button and select the ADC1105.exe solo configuration software.
Under the Graphics Mode: Resolution: select 1024×768 We can leave the rest to the defaults as shown below. Now Click Create Shortcut. Put the shortcut in the same directory as the software that was downloaded.
We will receive notification that the shortcut was created. Click OK.
Our folder will now look like this.
Click on our shortcut (ADC1105 (at 1024×768)) to start the Automation Direct Solo Series Configuration Software.
There are six icons on the main menu. Follow these in order from left to right to set up or troubleshoot your system.
Under the Com port setup, we configure the serial port of the computer to communicate to the Solo. In our case we will use COM5, 9600, Even, 7 Data Bits, 1 Stop Bit, Modbus ASCII Format.
In the Configuration menu, we will select the address of the controller that we will be communicating. This will be the default of the Solo which is 1.
Selecting Connect will then communicate to the Solo process temperature controller and you will see on the screen a picture of the controller with the PV, SV and indicator lights active.
This screen will now allow you to set up all of the parameters in the Solo. Once you enter a value it will be red on the screen. After hitting enter on the keyboard and the value will then be sent to the controller and be displayed in black again.
The recorder screen is used to monitor the temperature over time. You can monitor up to ten Solo Controllers at once.
Command Test is used to send individual Modbus command out. This is done in Hexadecimal.
The software for the Solo Process Temperature Controllers is very functional. Using the Reso software, you will be able to put the Solo Software in the 1024 x 768 that it was created for without manually changing the screen every time.
If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.
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