October 23, 2017 at 6:44 pm #1200RFMicronRFMicron Ambassador
The read range of a sensor is the maximum distance over which a sensor can communicate with the reader. To operate, a sensor must receive at least a minimum amount of power from the reader, as indicated by the orange line in the plot below. If the power received by the sensor is below this threshold, the sensor will not be able to communicate with the reader.
The power (in watts) received by the sensor declines as the square of the distance between the sensor and the reader’s antenna. This is shown by the blue curve in the plot. Over short distances, the received power is much greater than the threshold, resulting in successful communication. The power in excess of the threshold is wasted. The farther the sensor is from the reader, the lower the power it receives. At distances beyond the maximum read range, the communication breaks down.
Curve showing the power received by the sensor relative to distance from reader
Maximum read range varies from sensor to sensor. The design of the antenna and circuit of the sensor define the upper limit of the read range. This is the read range advertised in our datasheets. Environmental factors such as noise, multipath reflections from surrounding surfaces, objects between the sensor and reader, moisture, the material on which the sensor is placed, reader output power, antenna gain and polarization, receiver sensitivity and proximity to metals can adversely affect read range. Depending on what factors are at play, sometimes the read range can be shorter than expected.
To maximize your read range in a real-life situation, experimentation is necessary. Under adverse conditions, a read could fail even at short distances, but this may be remedied by changing the environment. Removing interfering objects, orienting the sensor differently, or even moving the reader/antenna might be necessary to achieve the maximum read range.
Our flexible sensors can work over distances from 4 to 9 meters. Usually our RFM3200 sensors have a maximum read range of 7 meters. However, our longest-range sensor is the RFM3240 Long-Range Rugged Wireless Temperature Sensor, which can be read from up to 19 meters away.
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