How power will be transmitted wirelessly to wireless transmitters

As an alternative to battery power, wireless power transfer improves process control and can pay for itself through reduced variability and higher profitability.

By Henry W. Boger, consultant

Imagine it’s 2022: XYZ Process Automation announced today at Hannover Messe the launch of a full complement of process control instrumentation based on wireless power transfer. XYZ spokesman Kurt Schindler said, “This is the dawn of a new age in process control. Although wireless transmitters have been available from several suppliers, these have required batteries for power supply, with the necessity to replace batteries periodically, and with compromise in update timing of measurements to extend battery life. Now, power will be provided to each device from one or more radio frequency (RF) transmitters. Each process device will be equipped with a suitable RF receiver, which will provide power to the device. A power storage element, such as a capacitor, may be included. For the first time, a wireless digital valve positioner (controller) is available with sufficient power to operate the control valve. This technology is based on a landmark patent application by Boger 1. Be aware that patent protection of this technology is in force.” At the XYZ Process Automation exhibit, a live demonstration is ongoing, and is attracting a great deal of attention.

This fictional announcement is describing RF power transfer. Wireless power transfer (WPT) can be achieved for medium- to long-distance applications by using microwaves. Microwave energy is focused on a location by a power transmitter having one or more adaptively-phased microwave emitters. Rectennas within the devices to be powered receive and rectify microwave energy for use as primary power.

Rectennas within the devices to be powered receive and rectify microwave energy for use as primary power.

Shinohara 2 describes myriad technical advances in wireless power transfer, as does Wikipedia. These range from the familiar inductive coupling for charging handheld devices to powering a helicopter, a fuel-free aircraft, power transmission over long distances (to islands, for instance), or to a microwave-powered space station.

As proof of concept, a wireless power transfer example was set up under laboratory conditions. A 5-watt RF transmitter was used to provide power to two receiving modules. The transmitter had a beam width of approximately 20°. The modules each measured ambient temperature, humidity and light, and transmitted wirelessly to an electronic board connected to a host laptop computer. The transmitted values of temperature, humidity and light were shown as a line of data on the computer screen. Update timing was dependent on the distance from the transmitting antenna to the receiving modules. The measured power was on the order of 50 milliwatts. This may seem low in efficiency, but digital process devices today can run on less than 50 milliwatts.

Blevins et. al. 3,4 fully report on the use of battery-powered wireless devices in the process industries. The authors focus on process control, including examples of applications showing results of testing. The results highlight the advantages of wireless, and underscore the limitations imposed by battery power.

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The most important benefit of this technology is improved process control. It's not necessary to compromise measurement update rate, and this will contribute to reduced variability. Blevens et. al. 4 state, “Reduced variability can provide a competitive advantage in manufacturing and lead to higher operating profits. As an example, some processes have a maximum allowable operating pressure (MAOP), and the closer to the MAOP that the process operates (without exceeding the MAOP), the higher the profit. By reducing process variability, it is possible to operate closer to the MAOP.”

The good news is that wireless power transfer can pay for itself through reduced variability and higher profitability. 

References:

  1. U.S. Patent Application 2016/0352145
  2. Shinohara, N., Wireless Power Transfer via Radiowaves, Wiley, 2014.
  3. Blevins et. al., Wireless Control Foundation, ISA, 2015.
  4. Blevins et. al., “Choosing the Right Communications Protocol,” Chemical Engineering , Nov. 2016

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