All-in-one PLC + HMI benefits manufacturer of boiler controls

Energy Plant Solutions of Palmerston North, New Zealand specialises in the supply and installation of industry energy plants and the company required cost-effective automation for its range of package boilers. In particular, Energy Plant Solutions wanted to standardise on a PLC and HMI in a single package to reduce the time required for developing boiler control systems. At the same time, the company wished to avoid paying inflated annual subscription fees for development software.

The major role of the PLC in this application is to control all of the functions of the boiler - such as the feed pumps, pressure control and level control.

All-in-one PLC + HMI

Energy Plant Solutions selected the Unitronics Vision1040, which interfaces with the burner via discrete I/O and Modbus. Discrete I/O is used for safety-related functions, such as shutting the burner down on low level alarms. Modbus is used for informational purposes, including actuator positions, burner fan speeds, flue gas residual oxygen, fuel valve states and fault details. The V1040 is also connected to the factory network via Ethernet. Modbus IP is used to transfer data to Wonderware InTouch SCADA.

The boiler control system also includes an Enfora GSM modem for SMS messaging. In the event of a fault condition on the boiler, an SMS message is sent to a list of operators (in sequence) to inform them. An operator can respond to the message to prevent the message being sent to the remaining operators on the list.

Also making good use of the SD card functions, Energy Plant Solutions is storing trend data and backing-up set points. This allows for quick recovery in the unlikely event of a hardware failure.

Why the Vision1040?

The Unitronics V1040 provided the right balance of screen size and number of physical buttons, as well as communication ports. Because Energy Plant Solutions was using the EX-A2X along with two IO-DI16, two IO-RO16, two IO-AI8 and two IO-AO6X I/O modules, the large screen provided ample room to display the required information while keeping the fonts and elements large enough for easy reading. The physical buttons means most buttons are always available without consuming any of the space on the screen. This also helps with keeping the screen clean.

Justin Butler, a Senior Electrical Engineer at Energy Plant Solutions, comments: "There were significant cost savings using the Unitronics PLC. This is for both the development software licensing (it does not get much cheaper than free) and also in the time required to develop the PLC/HMI software. Making changes is so much quicker when you can add the necessary logic to the PLC program and then immediately add the new elements to the HMI without having to export or import tag data, etc. Also if we need to move some operands we can do it in a single step and the changes are made to the PLC and HMI code immediately.

"With Remote Operator, we can see exactly what the operator sees from our office at the other end of the country via a VPN at absolutely no cost either financially or in development time. This is a huge advantage if the client requires assistance to solve a problem. Because the PLC and I/O modules are all 24V DC, we were able to use a 24V DC uninterruptible power supply (UPS) to maintain power to the PLC and I/O on power failure. Because the UPS does not need to step the power up to 230V AC before being stepped back down again, we achieve maximum up time afforded by the batteries. It is also safer because there is no 230V AC present when the main power supply is disconnected."

The SMS system sends the operator an actual description of the fault, rather than just a generic 'boiler fault' message. This enables the operator to make a decision on how quickly he needs to attend to the fault. The fault messages on the HMI and SMS are the same and come from the string library - therefore they do not need to be coded twice.

Butler continues: "Unitronics PLCs allow us to run the PLC without any I/O attached. This is great for testing before the system is deployed on site. This works like a simulation where we can enter any values we like for conditions and test that the PLC acts as intended. We can also check that all the graphics work and look good on the actual screen that will be used. This means we can do 90 per cent of the testing before we even go to the site.

"Working with the Unitronics combined PLC and HMI make other systems feel old fashioned and obsolete. The support from Unitronics, from our local supplier, to email support, to help ideas on the forum, has been absolutely fantastic."

Follow the link for more information about the Unitronics Vision1040.