Historically plant instrumentation has communicated using an analog 4-20 mA signal. As instruments gain more sophistication, additional information has been made available by taking advantage of protocols like HART (a protocol with digital signal imposed over the analog 4-20mA). This allowed the addition of other variables and  diagnostic information to be sent from a HART enabled device to a HART enabled system.




This technology was pushed further with the introduction of WirelessHART, which is an all-digital wireless communication. All WirelessHART instruments automatically send diagnostic information with every transmission in addition to the four variables sent with the instrument. This information is received by a WirelessHART gateway which integrates the instrument data to the plant control system. It is up to the vendor to ensure the information that is being sent with their instrument is meaningful and actionable.




Often we find that users are not fully aware of the capabilities of these wireless systems with their legacy systems communicating with protocols like Modbus. It is important for users to understand this because it helps alleviate very important questions regarding wireless digital communication. Questions such as: how do I know the instrument is communicating? With instruments like gas detectors, the normal operating state is to be at 0 and should be at 0 unless gas is detected, only introducing a value when gas is detected. Or a common question with all instrumentation, if the device is in a fault state, how do I know what the fault is? The additional diagnostics offered with WirelessHART can often answer these questions.


As the industry continues to move towards wireless communication, take advantage of the upgrade and utilize the information already available to know more about what is going on in your plant with your instruments and tools that are already available to use.


Written by: Andrew Liptak- Gas Detection Product Manger at United Electric Controls

Email: aliptak@ueonline.com

andrew liptak

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