At two meters the book is less well lit and may be difficult to read and at three meters, too dark to read. If you turn on a small light in a room and place a book one meter away, you may find that the book is well lit and legible. The role of distance in weakening a radio signal is analogous to the effect of distance on visible light. A signal strength less than -75dB will still work, but not at the 99.995% reliability that Emerson aspires to. This is a very conservative figure that leaves headroom to overcome temporary changes to the environment that reduce signal strength – obstructions, noise or even heavy rain. We recommend a signal strength of -75dB to maintain a highly reliable communications link. For a reliable radio link, the received signal needs to be stronger that the minimum strength that the receiving radio can detect, and stronger than any noise.Įmerson instruments and the wireless gateway measure and report the incoming signal strength as a “Received Signal Strength Indicator” or RSSI. Eventually, the signal reaches a receiving antenna that amplifies the signal (and any noise) before the signal reaches the receiving radio. As the radio waves travel, they will hit objects that absorb or reflect some of the signal, weakening it. ![]() Even directional antennae transmit in all directions, just much stronger in one direction than others. ![]() The radio waves (electromagnetic) then travel outwards in all directions. Let’s look at radio signal strength in theory, and then a practical example.įor a simple wireless path, the transmitting radio generates a signal at its nominal power level, which is then amplified by its antenna. Interestingly, in an industrial setting, distance is only a part of the story and is not a determining factor for the suitability of WirelessHART for the majority of installations. Emerson’s Craig Abbott provides some technical considerations for your IEC 62591 WirelessHART field device network.Ī frequently asked question about the WirelessHART 2.4GHz radio network is “How far can these devices transmit?” Depending on local units of measurement, the rule of thumb distance for the standard antenna is 225 meters or 750 feet.
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