Induction melting furnaces: benefits of integrating HMI and PLC

Industries specifically dealing with extraction and purification of metals have switched from traditional methods to using induction melting furnaces. The integration of HMI and PLC is proved to improve the process.

By Charlie Parsana, Electroheat Induction August 22, 2014

Induction melting furnaces have proven to be effective in the primary industry. Industries specifically dealing with extraction and purification of metals have switched from traditional methods to using induction melting furnaces. However, there are certain enhancements which, after being integrated into the induction melting furnace, tend to improve the process by perfecting every aspect. To learn how HMI and PLC benefit your operations, read on.

Understanding HMI and PLC

The two enhancements offer better control over the induction melting furnace. Traditional methods involve considerable human contact, which could be dangerous at the same time. That’s where the human machine interface (HMI) and programmable logic controller (PLC) reduce any chances of unforeseen hazards from materializing.


The HMI acts as a bridge between the user and the machine. The software bridges the two so that the user has a graphical display he or she can use to control the furnace. The display provides details about the machine along with the facility and processes so that it can be controlled and monitored properly.


The system automatically controls the work, and based on the operator’s needs, it is balanced accordingly. Considering the dangerous scenario that the workforce needs to operate in, the system acts as a barrier to protect itself and the individuals operating it from harm.


The benefits of the respective systems are endless. You will notice a considerable change within the operations once they are in place. These benefits will surely make you reconsider your opinion about induction melting furnaces being the ultimate tool for metal processing industries. Some of the benefits they provide are as follows:

  • With enhanced tools at your disposal, the task of operating the system becomes much easier. You can analyze problems quickly and without any hassle. The graphic interface provided illustrates every detail, giving you a better perspective about your operation and how it is lacking in terms of productivity.
  • These systems work independently, without any operator interference. Although it is necessary to predefine configurations, once that’s taken care of the whole process is automated, reducing any human contact with the potentially dangerous environment.
  • Based on your requirements, you can configure the system in a way that the sintering cycle meets your standards. It is obvious that not all processing industries operate the same way. With better control you can operate based on your production methods.
  • These systems are quite user-friendly. Not only are they easy to use, but they also can be operated without any specialized training. In addition, the variety of languages to choose from makes it easier for the workers responsible for maintaining the equipment to understand the operations.
  • In case there is a problem in the production cycle, it becomes easier for you to diagnose the problem before it can cause extensive damage. Using features like online interlock along with tripping navigation, you can easily diagnose the problem even though you may be miles away.
  • These systems can be accessed through the Internet. This means you can access them from anywhere around the world, at any given time. The systems are a suitable venture for any industry, and they also reduce the chances of any delays that could cause loss of revenue.

1. Welcome screen

  • This is the 5-second countdown timer. The delay is purposefully set to allow the normal start-up of the microcontroller and power supply to become stable.

1.1. Main Screen

Ready: The lamp will glow green when all the interlocks are healthy. This lamp turns red when one or more interlocks fail and the inverter is switched OFF. The user may navigate directly to the Trips/Interlock screen by touching the Ready lamp.

MCCB ON: The lamp will glow red when the MCCB is ON. Power Source Ready and Heat ON is possible only when MCCB is ON. This also implies that the machine is electrically Live and no part inside the panel or coil can be physically touched.

Heat ON: It indicates that the Power is ON and that the Power is fed to the coil. This lamp turns OFF when the Heat OFF pushbutton is pressed and/or Ready goes off and/or a Trip is generated.

Limit: Turns to yellow when the equipment is running at its maximum voltage or current capacity. The lamp glows when the equipment is operated in one of the following limit conditions. Under the conditions the output power cannot be increased further even if the Power pot is set to maximum value. This is because the maximum safe operation limit of various power components is achieved and inverter controlling parameters are now set to prevent them from exceeding these safe limits. Refer to the following table for further details about the types of Limit and their implications.

  • Trip: Turns to red when the equipment trips due to excess voltage or current or other short-circuit problem. Refer to screen No. 9.3 (Trip Signal) for a detailed explanation. The screen can also be navigated when the Trip Lamp is touched.
  • A DC: Shows the dc current in the Rectifier section of the equipment.
  • V DC: Shows the dc voltage in the Rectifier section of the equipment.
  • A Inv.: Shows the Inverter output current.
  • V Cap.: Shows the voltage across the Melting coil.
  • Hz.: Shows the frequency at which the equipment is working, in Hz.
  • PWR Ref.: Power reference set by power control potentiometer, in kW.
  • Min: Shows the Heat ON period of present heat.
  • Heat No.: Shows the number of heats already tapped since 00.00 hrs.
  • IPF: Indicates inverter output power factor.
  • KWh: Units consumed during present heat. It reset to zero and restarts when the Heat End button (in heat report screen) is pressed.
  • Power (kW): Shows the actual power drawn by the equipment, in kW.  
  • -||- or -^^- Indication: This symbol indicates that the equipment is working in capacitive (-||-) mode or inductive (-^^-) mode. This is an informative indication.
  • EL Amp: The vertical bar graph shows the Leakage current flowing to the Earth ON scale of 0 A to 10 A. The green line indicates the maximum allowable EL current set by the user, while the right side orange Line indicates the instantaneous Leakage current in the system. Ideally, the system should be set at Leakage current up to 2 A. The middle bar shows the maximum value of instantaneous EL current. Maximum value can be reset by pressing the RESET pushbutton.

1.2. Interlocks

Ready interlocks:

The healthy or the inactive state of this interlock indicator is green in color. In case of active signal, the display will turn red. Each indicator is displayed as two different indications.

  1. A small square indicator signal in the main interlock box: This red color of this box shows that the corresponding fault is still not cleared. The green color of the box shows that the fault is cleared but the operator needs to acknowledge it by pressing the Reset pushbutton.
  2. The main interlock display: The green color shows that no fault exists and the equipment should be in Ready state. The red color shows that the fault is not attended by the operator or the fault is not acknowledged by the operator after it has been cleared. The operator needs to acknowledge the fault by pressing the Reset button on the control panel.
  3. The user can touch the corresponding interlock to direct to another screen showing a brief description as well as the photograph of the interlock sensor.

These interlocks are briefly described below:

1.3. Trip signal

Trip indications:

The lamp indicates that the respective trip is generated. This will also switch OFF the heating/melting process from the operation. There are two types of trip:

  1. Hardware trip: Under the column HARDWARE, the trip is generated when OT-DTM has detected the high value of the specified parameter.
  2. Software trip: Indicated under the column SOFTWARE, the trip is generated when the microcontroller detected the high value of the specified parameter while processing.

The trip indications are briefly described below:

Considering these advantages, it is safe to assume that these modern techniques have evolved to the extent that they are fully capable of operating on their own while maintaining efficiency.

Charlie Parsana is the project engineer at Electroheat Induction, headquartered in Jersey City, N.J., Electroheat Induction is a provider of custom induction melting furnaces, induction heating and hardening equipment, and pipe heating products.

– Edited by CFE Media, see more PLC, HMI stories below.