Many pieces of the control system require dc power in order to operate. This could include sensors, motors, solenoids, valves, PLCs, controllers, HMIs, remote I/O racks, industrial PCs, vision systems and network gateways. However, after the dc power system is designed and the devices are purchased and placed in the enclosure, they are forgotten. Maybe they are given a token look every now and then to make sure the LEDs are blinking, but, as long as the system is functioning, all is good. But what happens if there is a failure with the 24 V power system? A power-supply failure for a critical process controller or device can lead to an unplanned shutdown of critical plant equipment or processes. Without critical event visibility, plants don’t have the necessary tools to troubleshoot issues before they become catastrophic. Fortunately, there are solutions to these problems. Now there are power supplies that can give you a window into their health.
Jay Hendrix is Product Marketing Manager —Connected Power for SolaHD, Emerson. He is responsible for product vision, strategy and development for SolaHD connected products. He has more than 30 years of industry experience in product management, building controls and technical integration. Hendrix holds a bachelor’s degree in electrical engineering technology from Purdue University and a master of business administration from DePaul University.
Q: What are the benefits to monitoring 24 Vdc power supplies?
Product Marketing Manager—Connected Power,
SolaHD, Emerson
A: Connectivity provides a window into your power supply’s health helping avoid unplanned disruptions and shutdowns. The connection to your power supply allows key diagnostic information to be communicated on the network to the control system. Along with diagnostics, key power-supply alarms alert operators when critical events are occurring. Insight into monitoring trends and responding to alarms enables operators and service technicians to anticipate maintenance needs, keeping your facility up and running.
Q: What about a power supply that has a DC OK contact; isn’t that good enough?
A: The DC OK relay contact is used to alert an operator that the power supply output power is good. The relay would open on a loss of dc power. This is useful for redundant operations or potentially in a safety shutdown sequence. However, at this point the dc power is already lost and any chance of identifying and catching an issue in advance is gone. This is an after-the-fact indication.
Q: Why is it important to monitor a 24 Vdc power supply? What can a smart power supply tell me?
A: In critical production processes within a facility, a power interruption or failure to a process controller could result in catastrophic loss. The slightest process variability could affect the complex reactions of multiple components, leading to substandard and unacceptable final product.
Using connected power supplies enables operations to monitor critical power parameters and key alarms, look for unbalanced loads and abnormal conditions and improve overall equipment effectiveness (OEE).
A connected power supply can provide real-time parameters such as input/output voltage and current, power-supply temperature, power-supply alarms and events and useful-life information.
Q: What are the factors that affect the life of a power supply?
A: How hard the power supply is stressed throughout its life affects its longevity. This will include the power-supply load and environmental temperature. Heavy load and high temperature are the factors that will shorten power supply life.
Q: How long should a typical power supply last?
A: Under normal circumstances a power supply will last 10 years, so how should you estimate the actual expected life of a power supply? Power supplies that support communication may be able to provide lifetime operating hours. This value can be compared to the power-supply specifications to gain insight into remaining life. Some power supplies may provide an indication of expected remaining useful life. This may be a percentage value that counts down over time or thresholds of life left. The countdown percentage is similar to the oil change indication in your car.
Q: What protocols are available for smart power supplies?
A: The typical industrial protocols are available in the market, depending on the supplier. Some of the common protocols that run on Ethernet are EtherNet/IP, EtherCAT, Profinet, and Modbus TCP. Highway-addressable-remote-transducer (HART) protocol is widely used in process automation and may be an excellent option. IO-Link is a short-distance point-to-point protocol. Some suppliers have adopted IO-Link for power-supply communication.
For more information, visit www.solahd.com.
