Wireless Wasted with Thumbs

The most common implementation of Industrial Wireless, especially WirelessHART is to install a “thumb” on the ‘spare’ outlet of a conventional HART transmitter so that the HART information can be accessed wirelessly practically anywhere. In my mind this is a step back because most control systems support HART communications directly via their AI and AO cards. Why therefore would you install a parallel system to access the information available directly from a wired connection you already have?


If your control system’s I/O cards do not have a native HART modem, wired “HART strippers,” basically smart terminal blocks, have been available for a number of years to use RS-485 or another network to bring the diagnostic information back to an asset management system to make full use of the data.
If you are like most people (approximately 80% of installations do not make effective use of their HART data) and simply consider a HART handheld communicator as a replacement for a screwdriver, I am sure your technicians must be able to access the device from grade somewhere along the loop so there is no need to have a more expensive wireless handheld and full infrastructure (access points, etc.) because there is no access to the wire.

The best thing about the thumb implementation is that you do not need to worry about batteries because the system scavenges power from the wired analog loop. I suppose you could also make a case that if you wanted to access the HART data without installing the “HART Stripper” system which requires lifting and landing every wire that might be valid as well though hardly an economic reason to install a complete wireless infrastructure. (It might be argued that it could be a risk management decision however.)

HAPPY CANADA DAY everyone!

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  • Kanduski, have you priced a wireless HART adapter? Compare it to the cost of a HART multiplexor. I just brought in about 200 HART points from an old ESD system that doesn't support HART IO, for less than $90 per point, using "stripping" term assemblies with RS-485 data gathering. That includes labor! Try to get a Thum or any of its competitors for less than $100.

    As for lifting and landing every wire - I think this is likely even with the "Thum" since the wires are co-terminated in the device, aren't they?

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