In a previous blog post, "General Characteristics of HART Communication", I went over the important aspects of HART, which is a wired communication technology that has been in existence since the 1980s. Naturally, technology does progress, and just like telephones moving from land lines to wireless, wired HART is moving to WirelessHART. Let's explore what you should know about WirelessHART, and what improvements it can offer to your plant communication.
First off, we're all pretty comfortable now using wireless technology in our day-to-day living. You probably have a smartphone, maybe a tablet or laptop at home using a wireless router to connect to the Internet. Your TV and programming might also be wireless. When it comes to HART, around 35 % of installed field devices use HART communication. Based on our most recent data, that equates to perhaps 42 million field devices using HART.
When you buy a standard 4 mA...20 mA field device today, about 70 % of manufacturers include the HART communication protocol built right into the device. DCS systems and AMS systems also typically have a HART interface. Since HART has been around for a while and is well established, it's considered a standard in the process automation world.
When WirelessHART was developed, the legacy of HART communication was a key consideration. WirelessHART needed to offer an open and interoperable standard. The newest revision of HART, Version 7, has added a wireless network as an alternate physical layer to the conventional 4 mA...20 mA loop used by field devices. There are many manufacturers out there for these types of products. You should be able to buy from any of them, and the products should all play nice in the sandbox together. It shouldn’t matter where the products come from. They go into your plant and work together as long as they meet the agreed-to specification that has been set up by the HART Foundation. Regardless of source, these field devices will work, talk, and function together.
Wireless HART also:
- Is as easy to use as its predecessor wired HART
- Enables wireless access to existing HART field devices
- Uses the same procedures and the same configuration, maintenance, and diagnostic tools
- Is easy to learn. If you know HART, you'll know WirelessHART with minimal training
- Is usable anywhere in the world
- Uses hardware like radios, which are off-the-shelf available
The radio frequency for WirelessHART is 2.4 GHz ISM band. The advantages of this frequency are that it can be used worldwide, and no permissions are necessary. This band was dedicated early on to the scientific and medical community, so there are no charges or expenses that are paid for its use. It is freely accepted and used worldwide, and with a few rare exceptions, there are no restrictions for using it. The hardware is also low cost and available pretty much anywhere, due to the WLAN standard IEC802.15.4. The WLAN standard allows improvements to be made on the weaknesses of the 2.4 GHz ISM band, which is basically a limited range and, in general, decreased reliability of a wireless network.
The transmission range of the 2.4 GHz frequency is about 200 meters, which may seem rather limiting to you when you consider the size of many industrial plants. Don't worry, WirelessHART can work around this transmission range quite easily.
Another consideration is that you may have occasional conflicts if there are WLAN or Bluetooth chipsets operating nearby, as these also use the 2.4 GHz ISM band. This might affect the WirelessHART transmission reliability, and it may even be jammed by these other operations. As always, it is wise to be mindful of what else is going on nearby, so that you can solve these frequency problems before you start your project.
So if you're contemplating a move from wired HART to WirelessHART, keep in mind that WirelessHART provides a common standard for wireless automation in the process automation industry, and enables an abundance of new applications that will benefit process facilities and their operations.