In this nineth installment of our technical discussion of the WirelessHART protocol, we look at the smart devices which make-up the nodes of the industrial network and ask the question “Is a smart device really smart?”
How smart is your car?
When it comes to determining the intelligence if a network device, you might consider the IQ of your car. All cars can tell you something about their status: remaining fuel, current speed, engine temperature, etc. Most cars can tell you if a door is open or a seatbelt is unfastened. More recent models can also identify your location or warn you of an impending collision.
In the same way, network nodes in a WirelessHART network can communicate with the network manager to update its status. Is it low on power? Who are its neighbors? But just like a car can’t drive itself to a given destination (not yet, anyway), a smart device in a WirelessHART network cannot determine the path, channel, or time a message should utilize on the network.
Why smart devices are dumb
Smart devices have a lot of knowledge about themselves and their status, but not a lot about the network. Network information is concentrated in the network manager to save power. Requiring a node device to keep track of and calculate network traffic details would require more circuitry and consequently consume more power. Industrial network sensor and control devices simply can’t be that power hungry.
Generally, the nodes are smart enough to answer requests for status information and to utilize table information given to them by the network manager. Most of the time, the devices are purely table-driven devices. It’s like a washing machine in that you tell it what you want it to do, then leave it to go through the cycles on its own. It can communicate its status or tell you about a problem, but it can’t choose the cycle or fix itself.
The network manager
It should be obvious by this time even smart devices cannot operate effectively in a WirelessHART network without the network manager. Next-time in out technical discussion, we will examine the function of the network manager more closely.