Sense When to Go Wireless

What's the Point of Trying to Add Wireless Capabilities to Sensors and Related Components?

By Jim Montague

Wireless might be fine for gathering signals from out in the middle of nowhere, but almost any machine or production line is going to have power handy. This means a facility's communication network is likely right there, too, so what's the point of trying to add wireless capabilities to sensors and related components?

First, end users have an insatiable desire for meaningful data — including video — to help optimize their machines and production lines, but this information is produced in spots that are too numerous, costly, labor intensive and inaccessible — even if the wired infrastructure is nearby. Second, many machine builders and system integrators could be unconsciously limited by a mindset that dictates "you can't secure a signal if a cable isn't there," so they don't begin to seek all the potential data points they could collect and use.

SEE ALSO: What Is a Wireless Sensor Network?

"Wireless temperature sensors and water meters have been around a long time, and can be retrofitted with 5- to 10-year batteries," says Bob Gardner, wireless product manager at Banner Engineering Corp. "So for the past few years, we've taken them into the industrial world with our wireless I/O components or with wireless fieldbus devices such as data radios. And last year, we released our Q45 wireless sensors, which bake our wireless I/O and photoelectric eye technologies into one battery-powered device, which needs no configuration other than a dip switch to set speed, has a photo eye with a response time of 62 to 500 ms, and communicates wirelessly to a gateway when it sees a light or senses an object.

"The real sweet spot in wireless sensing is a response time of about one to two seconds and one to two years of battery life. It's hard to get there because this is exceptionally low-power sensing of about 250 µA at 3.6 V, which is 900 µW — or less than 1 mW. We've only been able to do it by custom designing and optimizing the optics, sensor electronics, wireless components and every other part of the device to run at the lowest power."

Justin Bessette, electrical engineer at Lord Microstrain Sensing Systems, reports his company's wireless sensors use batteries and energy-harvesting methods, which gather power from solar, vibrations and thermal sources. "We've been building low-power wireless sensors for about 10 years, but many customers also want time synchronization to prevent losing data," Bessette says. "So last July, we launched our Lossless eXtended Range Synchronization (LXRS) wireless protocol, which is based in IEEE 802.15.4, runs at 2.4 GHz, and offers 32 µs synchronization. This means we can catch up to data that's been delayed, and precisely control time to reduce power consumption. For example, if a rotating machine is moving a sensor in and out of a wireless zone, we'll still be able to pick up all the data packets." Microstrain also released three LXRS-compatible sensors in 2012, including a wireless accelerometer, analog input wireless sensor with seven channels and wireless thermocouple node for temperature monitoring. All three use batteries, but can switch to energy-harvesting mode.

Ironically, just as Power over Ethernet (PoE) can provide some low-voltage power via data wires, there are a few places where data can travel over power's infrastructure. "We've had short-range (5-25 mm), power and signal transmission in our inductive couplers for 20 years," says Will Healy, network marketing manager at Balluff. "They transmit between base and remote units via a reductive field on a frequency with the data encoded. Originally, we sent 50-100 mA across the gap. Now, we're up to 24 V and 0.5 A, and we're going to seek 2-5 A. A lot of automotive and assembly applications use inductive couplers in turntables and dial tables to get simple on/off signals from their sensors. However, a couple of years ago, we added IO-Link fieldbus to our couplers, which lets us get I/O blocks and analog signals from sensors on the other side. Now, we can get all kinds of status and operations data via IO-Link, and we're just about to launch the ability to fire in outputs across the gap, too, to do jobs like drive valves and collect more inputs."     

Beyond gathering traditional sensor points in more places, many users demand more frequent and data-intensive inputs, such as video. "Our two-year-old WirelessHART adapter hooks onto existing transmitters to get process and building equipment signals onto their networks inexpensively, and gets power from a 5- to 10-year battery or a local loop," says Justin Shade, product marketing specialist for wireless at Phoenix Contact. "We see a need for higher-volume data transfers for remote PLC programming and video surveillance, often from multiple Internet protocol (IP) cameras. So, this past January, we released WiFi radios that can run at 300 Mbps instead of the previous 56 Mbps."

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