WirelessHART (IEC 62591) is the first open wireless standard for process field instrumentation. Based on the IEEE 802.15.4 radio standard at 2.4 GHz, it uses a self-organising mesh network that has proven reliable in the harsh RF environments of process plants.

Why WirelessHART in Process Plants

WirelessHART solves the installation cost problem of traditional 4-20mA instrumentation: no conduit, no cable tray, no junction boxes. Payback periods of 12-18 months are common for new measurement points on existing equipment where running cable is expensive.

Common applications include:

  • Remote temperature monitoring (heat exchangers, tank farms, storage vessels)
  • Pressure monitoring on inaccessible equipment
  • Flow measurement where cable routing is impractical
  • Corrosion monitoring probes
  • Rotating equipment vibration and temperature

The WirelessHART Mesh Network

WirelessHART devices form a self-healing mesh. Each device can route messages for other devices, providing multiple communication paths to the gateway. If one path is blocked (by interference, equipment obstruction, or device failure), messages automatically route through alternate paths.

The network manager (inside the WirelessHART gateway) manages:

  • Channel hopping across 15 of the 16 IEEE 802.15.4 channels to avoid interference
  • Time-slotted communication (TDMA) for deterministic latency
  • Join and leave procedures for adding or removing devices

Update Rates and Latency

WirelessHART is not a real-time control protocol. Update rates of 1-60 seconds are typical. Do not use WirelessHART for control loops requiring fast response. It is ideal for monitoring, trending, and process optimisation applications where 1-second resolution is adequate.

Security

WirelessHART uses AES-128 encryption and authentication at the device, network, and application layers. All three keys (join key, network key, and session key) must be managed. Most gateway vendors provide centralised key management. Disable devices immediately when removed from service to prevent the use of stolen devices to join the network.

Integration with DCS

WirelessHART gateways connect to the DCS via Modbus TCP, HART-IP, or OPC. Emerson’s Smart Wireless Gateway integrates natively with DeltaV. Honeywell’s OneWireless supports Experion. Most other DCS vendors use OPC DA or Modbus TCP for gateway integration.