What is the Range of WirelessHART?
A common question about the WirelessHART 2.4GHz radio network is, “How far can these devices transmit?” The general rule of thumb for the standard antenna is a maximum range of 225 meters (750 feet). However, in industrial environments, distance alone does not determine the suitability of WirelessHART it’s the overall reliability and adaptability of the network that matter most.
How WirelessHART Transmission Works
WirelessHART devices communicate by transmitting signals via radio waves. These signals travel outward from the transmitting antenna and weaken as they encounter obstacles like walls, equipment, or environmental interference. To ensure reliable communication, the Received Signal Strength Indicator (RSSI) is used. For WirelessHART, a signal strength of -75dB or better ensures a highly reliable link with 99.995% communication reliability.
Distance and Signal Strength in WirelessHART transmitter
Radio signals weaken as they travel further, following an inverse square law. For example:
- At 1 meter, the signal is strong.
- At 2 meters, the strength is 1/4 of the original.
- At 3 meters, it’s 1/9 of the original.
In open environments, the standard WirelessHART transmitter achieves its maximum range (225 meters) at -75dB. Using high-gain directional antennas, much longer ranges can be achieved, but this isn’t practical in most industrial settings.
WirelessHART in Industrial Settings
In complex industrial environments, obstacles like walls, pipes, and equipment can significantly reduce signal strength. For example:
- A typical office wall can reduce the signal by 6dB.
- Passing through two walls can reduce the range of a WirelessHART device to 56 meters.
This is where WirelessHART’s mesh network shines. Each device in the network acts as a repeater, relaying signals between neighboring devices. This design allows the network to bypass obstacles and maintain communication over longer distances. For example:
- A 700-meter span can be covered using three 225-meter hops, each maintaining strong signal strength.
Advantages of WirelessHART Mesh Networks
- Signals can route around or over obstacles, ensuring reliability.
- The network adjusts itself as the environment changes, like new buildings or equipment being added.
- Each repeater amplifies the signal, maintaining strength across multiple hops.
- Even in dense or complex environments, the network can sustain connectivity by using multiple short hops.
Practical Recommendations
- For light-density infrastructure, space devices up to 150 meters apart.
- For medium-density areas, reduce the spacing to 75 meters.
- In high-density industrial plants, a spacing of 30 meters is ideal.