Answering Common Questions about Wireless Instrumentation - Emerson Automation Experts

Answering Common Questions about Wireless Instrumentation

As technologies advance through the adoption phases and into mainstream use, a common set of questions usually emerges. For example, as the IEC 62591 WirelessHART communications standard has moved from its introduction to the market in 2007 to present day, its use has increased widely across industries, geographies and applications. We’ve chronicled many of these stories in the wireless category of this blog.

Emerson's Dale Perry

WirelessHART-Q-AI share this background to highlight a great EE Publishers article, Q&A – Wireless technology in process applications. The question and answer session is with Emerson’s Dale Perry who addresses common questions about WirelessHART, a:

…self-organising protocol utilising a time-synchronised, self-organising, and self-healing mesh architecture.

From the article, I’ll highlight a few of the most common questions I see in my travels through the social networks, and leave the rest for you to read if you’re interested.

How far the wireless communications can travel is a common question. Dale responds:

The transmission distance between two wireless devices is a function of the antenna type and the distance the antenna is above the ground or the structure of the installation. The specified distance is 225 m for a standard antenna mounted 1,8 m above the ground/structure. Optional high gain antennas with transmission distances up to 1 km are available and should be mounted a minimum of 3,4 m above the ground/structure. Since WirelessHART is a self-organising mesh technology with each radio able to communicate with all other radios, networks can cover much longer distances through “hopping” whereby transmitters closer to the gateway relay data for those further away.

Battery life for wireless instrumentation is another common question. He explains:

Contrary to most articles that seem to highlight only update rates affecting battery life, the radio actually consumes little power. Most of the power consumption in a device takes place when making the measurement. The more complicated the measurement or the algorithm to calculate the measurement, the more power is consumed. For example, a vibration measurement might require up to 60 000 samples per seconds for many seconds which takes a lot of power and will result in a shorter battery life. Conversely, a measurement to sample a voltage in a sensor will take very little power which equates to a longer battery life. Manufacturers have an online battery life estimator so users can approximate power draws and corresponding battery life for various measurement applications.

About the need for any special maintenance, Dale answers:

Wireless devices have the same maintenance and calibration requirements as wired devices because they use the same sensor technology as their wired equivalents. The only added maintenance is battery replacement, but this is more than offset by the elimination of wire and cable maintenance in most applications.

Read the article to find answers to other common questions including:

  • What does “self-organising/self-healing mesh” wireless network mean?
  • I heard that in a mesh network if route is blocked the data is routed through another route. How long does it take to switch to another route? Am I going to lose some updates?
  • What happens when the battery goes flat? Do I just lose that device and the part of my network that depends on that device to repeat/relay information?
  • Is wireless approved for safety shutdown applications?
  • Where can I use wireless devices?

You can also connect and interact with other wireless experts in the Wireless group of the Emerson Exchange 365 community.

Posted Thursday, March 26th, 2015 under Wireless.

One comment so far

  1. I personally agree that adding more measurement points is a good way to improve process uptime (i.e. equipment reliability) while at the same time reducing maintenance cost. Other important areas for WirelessHART are energy efficiency and reducing HS&E incidents and response time. Process operations productivity can also be improved.

    I personally believe that perhaps another even greater reason why wired sensors have not been deployed in existing plants to improve in these areas is not just cost but risk: the risk of damaging the existing installation when opening cable trays and junction boxes to lay more cable and connecting more wires. By going wireless, there is no need to open cable trays and junction boxes, so it is very low risk. This of course requires you to use a FULL mesh topology where every device is capable of repeating/routing data from other devices in up to 7 hops or more. This enables the plant to install the wireless gateway at the edge of the plant unit where the backhaul network and power can be connected with ease, without running wires in the middle of the unit. Only WirelessHART (IEC 62591) can do this. Other wireless instrument networks require multiple backbone routers to be installed inside the plant unit with power and backbone network wiring – the cable trays and junction boxes must be opened. The ease of deployment and high reliability of full mesh topology is what has made IEC 62591 so popular.

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