Summary: Grupo Electrotecnia Galiana’s challenge: create a high-performance test bench to test HVAC compressors over the word-wide range of voltages & frequencies, while enabling remote commissioning & operation via Web browser & VNC.
Their choice: Unitronics’ UniStream controllers.

Project Description

Control Engineer David Bragado of Grupo Electrotecnia Galiana in Madrid had a challenging project: a client needed a high-performance test bench, capable of testing HVAC compressors for the global market over a wide range of voltages and frequencies. The client also required Remote Access capabilities: operators must be able to remotely access and control the testing process.

Engineer Bragado had used Unitronics’ Vision programmable controllers in previous years for a number of projects in the water industry—but for this complex machine, he integrated a UniStream® USP-104-B10 PLC + HMI, a UniStream® USC-P-B10 PLC, and a selection of Uni-I/O®, in order to take advantage of advanced features.

Project Goals

HVAC compressors and needed a high-performance test bench, a machine to test each compressor before it leaves the factory. These HVAC compressors are manufactured for the global market—remember that countries have different power supply standards. Since, at the end site, the compressors must function at a wide range of different voltages and frequencies, the test bench had to be able to simulate any power supply in the world,

There are similar test bench machines with the same purpose, but not with this level of automation and performance. This was a new application, a project developed from scratch.

“I don’t think I could have done this project, which had so many different requirements, with any other single device.”
“The functionality and versatility of the UniStream controller series is impressive—and it saves lots of time. It is also amazingly easy to set up the Web server and the VNC server. This last one is an amazing tool for commissioning and operation. Setting up communications is also fast and easy!”

Our test bench needed to meet these requirements:

• Power: In order to simulate power supplies world-wide, the bench had to be capable of generating from 12 VDC to 460 VAC in 50 or 60 Hz with a maximum power of 250 KVA.
• Voltage Control: 3 power lines had to work simultaneously.
  UniStream had to provide accurate voltage at each output, by managing each individual line through separate sequences, commanding the speed drives, switches, contactors, variacs, and many other components.

The operator initiates a sequence by selecting the line (250KVA AC, 5KVA AC or 5KVA DC), frequency (50 or 60Hz) and the voltage to be set in the output.
After this, UniStream runs a sequence of steps: Closes some contactors, starts the speed drives if needed and closes the corresponding output of the transformer.
Once there is voltage in the output, UniStream automatically fine-tunes, regulating the voltage as close as possible to the set point. Depending on the load and the type of test, this voltage might change during the procedure, so the PLC continuously regulates the variacs in order to remain as close as possible to the set point.

• Data: There were also requirements for acquiring data in order to analyze it after the test. I used UniLogic’s built-in data functions to create timestamped datalogs of the tests, and then export them to .csv files for analysis.
• Remote Access: We needed to enable the operator to run tests while sitting in his office—or at home, for that matter. UniStream’s built-in VNC Server feature made this a snap, including commissioned the machine off-site, via VNC.

The main challenge was using a single controller to handle a long list of very different requirements and tasks. In addition to controlling the actual testing tasks, the PLC needed to handle communications - Modbus RTU and ModbusTCP, data logging and file handling, and well as enable remote operation.

There were specific challenges that I met by simply building my own functions—something that is very easy to do using UniLogic’s UDFB – User Defined Function Block – feature.

For example, I needed to regulate the variac. I could not use the built-in PID function because the variac is not an analogic actuator - it works by sending a digital command to increase or a digital command to decrease the voltage.

However, with UniLogic I was able to easily create my own PID function, which sent pulses to the variac according to the distance between the set point and the output voltage value.  When the distance between the set point and voltage is decreasing, the pulse width decreases. When the distance is great, the pulse width increases, continuously regulating the voltage in order to reach set point.

They also created functions to enable operators to operate individual system components for easy system maintenance. I built function blocks for the contactors and the variacs, integrating auto/manual, interlocks and fail-to-start features. Then I made a template HMI screen for all these objects; this allowed me to create unique instances simply by indexing the structure to be displayed in the screen.

I had another challenge regarding Modbus—specifically, with the response speed of the 5 Modbus RTU slaves in our application. I solved it easily, by changing three of them to Modbus TCP. After that, we had Modbus RTU and TCP working together—this turned out to be a good solution. We were able to substantially increase network performance just by making a few changes in the PLC. Communication configuration is very easy with UniLogic.

Unitronics Advantages

The big advantage is the high level of functionality. Engineer Bragado keep saying: “I don’t think I could have met so many different requirements with any other single device—and I didn’t need licenses, or any additional hardware.”

• Communication configuration is very easy with UniLogic. I could communicate through Modbus RTU and change some slaves to TCP easily and have both working with excellent performance.

• Function blocks: which were essential in this project—are easy to build and re-use.
• HMI screens: it was very simple to develop a single template screen for my function blocks, to allow every component to be operated individually.
• Data, logged then exported to CSV files with the time and date of the tests for the operator—I didn’t need a separate data logger.
• Remote Access & Control—one of the most important advantages—I was able to set UniStream’s VNC server to allow me to perform the commissioning remotely, and to enable the operator to easily control the testing from the office or his home.

This is a very valuable aspect!

Unitronics’ Technical Support

I used the Unitronics Support forum.

The people in this forum are just great. They are very active and they are always willing to help. And their technical knowledge is really incredible. I am grateful to them for their help. I asked questions regarding my Modbus issues, and also searched the forum for other information—very often, someone will have run into the same issue you are having, and the solution is posted on the forum.

Reaching Unitronics

In my previous company, I worked with a lot of Vision PLCs. We deployed dozens of V120 in wastewater treatment plants and water pumping stations all over Spain, to warn operators via SMS in case of alarms. We also performed a remote control project with 8 Vision deployed in different places and Indusoft Web Studio. When I arrived at my present company, they were already using Unitronics.

Choosing Unitronics

I think they are a perfect solution for these kinds of projects. Unitronics controllers are affordable, fast, clean, and you can breathe freely when you finish, because you know it all works. The durability of Unitronics PLCs is also amazing. I’ve seen V120s working for many years, under all kinds of harsh environmental conditions and treatment. I have experience working with other manufacturers, and it’s just too complicated, with different versions, different firmware, compatibilities, licenses, communication cards…

UniStream was perfect for this project—you have an all- in-one device, programming is very easy, communications are easy, the support is great and it has lots of functionalities.

David’s Personal Note & Summary

I am really proud of the result of the project. We built this great machine, unique in the world, and the Unitronics team is also responsible for our success, so thank you!

I don’t think I could have done this project, which had so many different requirements, with any other single device.

The functionality and versatility of the UniStream controller series is impressive—and it saves lots of development time.  It is also amazingly easy to set up the Web server and the VNC server. This last one is an amazing tool for commissioning and operation. Setting up communications is also fast and easy!”

More Info & References