Make your machines more energy-efficient: 5 basics

How to monitor, measure, and control the power consumption of industrial machines and production lines.

By Cindy Green, AutomationDirect

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Machine builders, OEMs, and system integrators are designing machines with energy-management best practices in mind. Atop the best-practices list is monitoring and measuring power use and then programming operation of machines, equipment, and production lines to reduce energy consumption.

Power consumption measuring and monitoring helps optimize facilities, production lines, and machine control – and knowing just where and when power is being used will help you identify where improvements are needed. Here are five keys to getting greater efficiency from your assets.

1. Commit to keeping track of your power use

The best way to determine power use is to monitor power consumption in real time, as it provides a means to measure actual, dynamic demand. This is important because machines use varying amounts of power depending on their operating mode or where the equipment is in its sequence.

Relying on the nameplate ratings for electrical equipment such as motors and drives will reveal only worst-case values; these aren’t a reliable measure of power consumption because actual energy use varies depending on the equipment and how it’s used. Machines typically consume power at a variable rate, and power supplies and servo drives and VFDs often use much less power than their nameplate ratings indicate.

Power consumption measurements help determine where energy use is the highest and point to areas for possible improvement. When a machine is stopped and waiting for product or downstream equipment, the reduced power use at idle can be recorded. The power usage also is recorded continuously during the machine’s cycle and at a variety of production rates.

When you have a comprehensive picture of your power use during production, you can better decide where and when to change a machine’s production state. If the idle state is using too much power, the machine can be shut down. Data analysis also may indicate that the machine can be switched to idle state while waiting for product instead of waiting in a ready-to-run state, with conveyors in motion and waiting for product, for example.

Power monitoring can highlight scheduling issues that are causing inefficient energy use. If an oven is heated and waiting for product for 30 minutes before cycling, then preheat can likely start at a later time. In a similar example, running an oven for only an hour’s worth of production when it takes 30 minutes to heat up is inefficient.

Monitoring and understanding power data can make it possible to run machines and processes that consume large amounts of power at off-peak hours to take advantage of lower electricity rates. This information can also be used to reduce demand charges, which many utilities assess based on peak power consumption.

2. Perfect your power monitoring

Power can be monitored manually with a handheld clamp-on ammeter and a voltmeter. However, these measurements require manual labor to access the equipment, measure the power, and record the values every time the data is collected. For the most basic power monitoring applications, manually measured power can be combined with an AC or DC current-operated switch. The switch becomes an input to the programmable logic controller (PLC) or other controller, and the assumption is that the measured power is being consumed when the switch is activated.

However, the required labor continues as the data is input to a spreadsheet, with the voltage and current converted to approximate power use. This power use data doesn’t include power factor, so the values will be accurate only if the power factor is at or near unity – obtained when current and voltage are in phase, a condition unlikely to be seen in industrial facilities. Although this is a good way to establish a power use baseline, there are other, more-accurate approaches to continued power monitoring.

A power meter can be connected to the load side of the main disconnect in the control enclosure of a machine or an item of equipment such as an air compressor. Modern panel-mount power meters can measure real-time, true power use. This measurement data can then be sent to the PLC or another controller and from there to a human-machine interface (HMI). Power meters typically have multiple communication options built in, allowing information to be transmitted via 4-20mA analog signals or via a single digital data link such as an Ethernet protocol.

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