Silicon-Controlled Rectifier Power Controls: Worth the Investment

Submitted by Randy Mulvaney || Valin Corporation
In the world of electric heaters, one of the most critical elements to consider is the control. Depending on the specific application, a certain level of control is not only desired but often required. In order to achieve adequate results, operators need to be confident that the process is reaching a specific temperature at the proper time on a consistent basis. Furthermore, the result cannot be at the expense of another function.

In terms of what matters to most in the field today, it is safe to assume that reliability, flexibility, accuracy and cost are at the top of the list. With these factors in mind, implementing a silicon-controlled rectifier (SCR) control system for an electric heater is often an optimal approach.

One of the first clear benefits demonstrated by an SCR power controller is the diagnostic capabilities inherent to the design. An SCR power controller can have the ability to detect malfunctioning or inactive heating elements in a given process. This detection and alert capability allows operators to see, in real time, that there is something amiss. This is critical to the overall effectiveness and cost of the process.

To illustrate, suppose there is an electric heater being utilized to heat a widget as it makes its way through an oven. For this setup, imagine there is a bank of heaters controlled by a power controller. In order for the widget to make its way through the process and come out on the other end without being over- or under-cooked, a reliable, consistent temperature must be achieved.

In this scenario, one of the most common culprits for temperature anomalies is when a heating element becomes unresponsive. Heating elements often pose this kind of challenge: One or more may cease to function for various reasons and, as most people can attest, these types of issues seem to happen in the middle of a production run. When one heating element fails, a few other events likely will be triggered:
  • The resistance will be increased on the remaining, functioning elements.
  • There will be an imbalanced electrical load.
  • The thermal dynamics will shift inside of the oven.
An SCR power controller can have the ability to detect malfunctioning or inactive heating elements in a given process.

An SCR power controller can have the ability to detect malfunctioning or inactive heating elements in a given process.

Typically, without SCR technology, a sensor will not pick up on a single heating element going out; thus, no action is taken. If another were to go out, however, the problems begin to compound. With even fewer heating elements attempting to make up the difference in heat that the process requires, the temperature controller would call for all elements to operate at full power to make up for the thermal shift. When these other elements are called on to make up the difference, however, they may not have the capacity — depending on how many have failed — to get the overall temperature where it needs to be. Unfortunately, this can be the reality for a long period of time, and it may go unnoticed by an operator. This means that for an extended period, the process being served by an electric heater is not outputting correctly.

The advantage of using SCR power controls in the above-mentioned scenario is that as soon as one of the heating elements stops working, it is detected immediately. It does not require two or three elements to fail before a sensor detects the issue. By continually monitoring the amps of the overall process, SCR technology will pick up on a missing heating element because it will inevitably change the resistance. This, in turn, changes the amps, and the SCR will alert an operator that a heating element is no longer functioning. By keeping the proper heat in a process without relying on other elements to make up the difference, operators can be assured that the output is consistent. This also helps eliminate the risk of skyrocketing costs due to unacceptable outputs and shutdowns.

The example provided is just one way to illustrate how SCR power controls can have a positive impact on cost reduction in an operation. By allowing an operator to be more alert to a failed heating element, SCR power controls ultimately will save time and money that otherwise would have resulted from an unplanned shutdown. This is not the only way SCR technology can cut costs, however. There are other cost-saving benefits to consider.

Without SCR power controls, operators would use a mechanical switch to turn the heaters completely off when not in use. However, this on/off action is not unlimited. In other words, there are only so many times one can turn the system on and off completely during its life before it negatively impacts the system, resulting in a necessary replacement. With SCR power controls, operators are able to dial the temperature up and down without completely shutting off the system, reducing the risk and consequences of the system suffering a thermal shock.

With more precise temperature control and avoiding complete shutdowns and startups, SCR significantly cuts down on the amount of overshooting and undershooting that occurs in the process heating operation. By significantly reducing these phenomena, the life of the heater will be extended.

The return on investment for SCR power controls is realized quickly as tighter temperature controls can be achieved.

The return on investment for SCR power controls is realized quickly as tighter temperature controls can be achieved.

Even today, SCR technology improvements are still being realized. Controllers are improved in their displays and configurability, further adding to their effectiveness. Some are user friendly and can be easily configured with software, even providing recommendations for certain controller settings. The biggest advantage that current SCR technology provides is the ease of integration, ultimately offering far less complex installation and wiring of systems. The designs of SCR power controllers also are becoming aesthetically sleeker and require less space to function.

The initial costs associated with implementing SCR power control technology into a given operation are becoming less and less of a concern for those in the industry. The return on investment is realized quickly as tighter temperature controls can be achieved. This leads to more consistent product being produced and fewer hours lost to downtime.

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