During the idle period on the weekend, it is common for equipment to still consume about 60 percent of the energy used during production. Up to now these consumers were typically not switched off. The reasons for this are complex. First and foremost, additional hardware would have to be installed outside the machine. Many users are reluctant to put in the engineering effort required for this. This situation can be avoided in the future by purposefully switching off "energy-wasting" components from the higher-level controller.

While external cabling is currently required for switching consumers, the use of equivalent commands eliminates this need. The consumers themselves "speak and understand" PROFIenergy—a cross-device and cross-manufacturer profile featuring the relevant energy-saving measures that is currently under development by PI. By relocating the switching operation to the device, the manufacturer can decide how to optimize its device for maximum energy savings. Up to now the use of a hard external switch-off meant that some consumers had to keep running during short pauses since they otherwise would not reach ready-to-operate status in time for the start of production. The new features and commands allow device manufacturers to react flexibly to idle times and, for example, to switch off just a few parts of the machine. In this way the potential for energy savings can be fully tapped.

Real-world energy management with PROFIenergy

In order to optimize application of the new profile in the real world, use cases (UCs) have been defined in close collaboration with users. These serve as the basis for the specification activities for PROFIenergy.

UC 1: Switching off and on during brief pauses

In this use case, the system selectively stops the equipment, e.g., during lunch breaks, and switches off those energy consumers that will save energy during brief periods but that can be powered up again on time. Accordingly, only individual devices or equipment components are addressed. Important safety-related functions are retained. When production operation starts, the system activates the consumers in a defined switch-on sequence and checks whether all consumers have started up correctly. The system then starts the production process.

UC 2: Switching off and on during long pauses

This use case is very similar to the first one. Because the pause is longer, however, additional devices can be switched off, and the devices internally switch off more consumers.

UC 3: Switching off and on during unscheduled pauses

In contrast to the two types of pauses examined previously, the timing and duration of the pause described in this use case are unknown. Interruptions due to equipment malfunctions are a typical example of this type of pause. For this reason, the energy demand is reduced initially as if for a brief pause. If it turns out that the repair work will take longer, the possibility exists to place the equipment into an even more energy-saving state.

UC 4: Acquiring measurement data

An additional use case is the acquisition of measurement data. In addition to measuring instruments in the true sense, a number of devices are currently built into equipment that measure energy values implicitly. Frequency converters are a typical example of this.

These four use cases represent the basis for additional applications. For example, PROFIenergy also allows a load-dependent machine control system as well as the avoidance of peak loads.

 

Simple handling

Handling couldn't be simpler. The user sends the device a command that indicates the duration of the idle time. The subordinate device then decides autonomously which parts can be switched off and still reach ready-to-operate status again when this idle time expires. It makes no difference whether the device is a single-component device, such as a drive, or a complex device, such as a machine tool.

To switch the device back to ready-to-operate status, the user only has to send a switch-on command. This enables the equipment to power up in a coordinated manner according to the respective application. The devices provide their power-up times to the user to enable a coordinated switch-on of devices with different power-up times. The user can thus calculate the timing for the switch-on command.

The demand for simple handling as a basis for widespread acceptance is thus met. The engineering effort is minimal. The user only has to integrate the two commands into his program. In so doing, the user can strictly separate the actual control logic for the process from the energy management. Device and system manufacturers can also support users by developing appropriate modules, for example, that cover the handling of ...