Reliability Using a Small PLC with GSM Modem


Written by:
Kevin Speed, Phoenix Contact

New equipment improves SCADA functions.

Innovative Control Technologies, Inc., (ICTech) is an independent supervisory control and data acquisition (SCADA) designer and integrator. ICTech’s services include a turnkey design and implementation of new SCADA systems, as well as optimization and expansion of the existing ones. 

The company has strong practical knowledge of automation and control system design—including telemetry, PLC applications and SCADA systems. ICTech is experienced in a multitude of HMI (human-machine interface) and hardware platforms.

Figure 1. ICTech installed the new PLC at about 20 remote locations. It provides accurate and timely alarms, improving the system’s stability.

SCADA Communication Drops

ICTech designed the SCADA control system for a water/wastewater facility in Utah. Originally, a SCADA alarm software would communicate with the SCADA/HMI software on an industrial PC at the control center. When an overflow occurred, the alarm program would send the alarm back to the SCADA PC. 

Occasionally, the computer would drop communication between the HMI and the alarm software. Unfortunately, no notification was given when this happened, so the operator would not know that communication was down. According to Igor Kovalenko, electrical controls engineer at ICTech, this created the potential for serious issues. 

“If we have overflow problems and do not receive notification, this could lead to major problems. If it is bad enough, it could end up being a story on the evening news,” he said.  

Kovalenko explained, “After installing the SCADA software on the computer, you have to run copper analog line. On top of that, this software was complicated and required a lot of programming.” 

A typical alarm dialer system requires a copper phone line, also known as plain old telephone system (POTS). Most software manufacturers do not have the resources to support all the voice over Internet protocol (VOIP) software, so they usually choose not to support any. 

This is cheaper for the software company, but the cost of running the copper analog line is time-consuming and expensive for the end user. 

PLC and GSM Modem Stop the Drops

ICTech worked with an industrial electronic technology provider to design and install a SCADA system based around the technology provider’s programmable logic controller (PLC) and its optional GSM modem.  

The new, chosen PLC was a small, flexible controller for simple applications. It used software for easy programming and hardware configuration. Several I/O and communication modules (including the GSM modem) are available for expansion. 

Kovalenko says that the modem’s advanced I/O and alarm capability were the key factors in the decision. 

“The Nanoline GSM modem could handle up to 60 alarms and offered the possibility to increase this number in the future,” Kovalenko says. “I couldn’t find another modem that could handle more than eight to 10 alarms. This would mean installing additional analog and digital, which would add more wiring and labor costs. Analog PLC is the most expensive option, but by using the Phoenix Contact modems, we were able to bypass this process.” 

ICTech installed the PLC inside panels at about 20 remote locations. All the remote locations communicate to the master PLC at the plant. The master PLC then communicates to the new PLC using an RS-485 serial connection to send and acknowledge the alarms. The new PLC does not communicate directly with the HMI. 

Because the alarm dialer and the HMI are separate, the new PLC communicates directly with the master PLC. This creates a more robust system that does not have to rely on a computer to send alarms.   

More recently, Robert Simons, ICTech’s programmer, created an Android application that automatically sends a pre-set text message to the PLC with the push of a button. The application also displays all the messages received from the PLC.

Figure 2. The GSM modem is one of several expansion modules available to make the new PLC even more flexible.

New System Produces Fewer Errors

Since it has been in operation, the system has run as planned. Kovalenko says that the new system has increased stability and reduced the possibility of errors. The GSM modem ensures accurate and timely communications, including critical alarms. 

“Having both alarms is the system’s most important feature,” says Kovalenko.  “This is exactly what I was looking for. If you flood a pump station, that can potentially lead to millions of dollars in loss. However, if you can react in time, there will be fewer problems.” 

He said that the new PLC’s output has proven more robust than the computer SCADA system on which the plant previously relied. 

“If the wires on the POTS line go down, it doesn’t affect our HMI, because we are connected directly to the PLC via the modem,” he states. 

An added benefit was that they did not need to hardwire anything. 

“We can install the new system anywhere that there is cell service. We no longer have to worry about running additional POTS copper lines.” 

Kovalenko noted that the original solution provided unlimited alarms. The new solution can only provide up to 60 alarms and 64 messages, but he says, “That is more than enough.” 

Another advantage was the modem’s built-in security features, including password access, caller ID blocking, messaging aging and watchdog timer security. 

“We didn’t have secure communication with the old system,” Kovalenko states. “Phoenix Contact installed security, so that only people with access can make notifications and changes.” 

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See also:

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