From a car’s reversing alert to a factory’s automated assembly line, distance sensors are the invisible technology that allows machines to “see” and measure the world around them. They measure the space between themselves and an object, converting this data into an electrical signal. But not all sensors are created equal. The technology you need to measure a water tank level is very different from that needed for a high-speed robot.
Furthermore, once you have the measurement, how do you get that data to where it needs to go, especially from a remote location? This is where modern communication technologies like LoRaWAN come in, transforming simple sensors into powerful, connected smart devices. This guide explains the main types of distance sensors and, critically, how to choose the right combination of sensor and network for your needs.
The Quick Answer
The most common distance sensors are Ultrasonic (using sound), Laser/Time-of-Flight (using light), and Infrared (using IR light). The right choice depends on your required range, the accuracy, the target material (solid or liquid), and the environment (indoors or outdoors). A separate but equally important choice is the communication technology. For remote, battery-powered applications like tank or flood monitoring, LoRaWAN is the dominant choice, offering long-range, low-power data transmission that other technologies like Wi-Fi or Bluetooth cannot match.
Understanding the Sensor Technology (The “How”)
First, you must choose the sensor itself. This is the component that actually performs the measurement.
Ultrasonic Sensors
Ultrasonic sensors work like a bat’s echolocation. They emit a high-frequency sound pulse and then “listen” for the echo. By measuring the time it took for the sound to travel to the object and back, the sensor can calculate the distance. They are excellent for measuring liquid levels in tanks or for detecting large objects, and they are not affected by the colour or transparency of the target.
Laser (LiDAR / Time-of-Flight) Sensors
Laser-based sensors, often called LiDAR or Time-of-Flight (ToF) sensors, are far more precise. They emit a single, focused pulse of laser light. The sensor’s circuitry measures the time-of-flight it takes for that light to hit a target and bounce back. Because light is much faster and more focused than sound, these sensors offer pinpoint accuracy and a much longer range. They are ideal for high-speed robotics, 3D mapping, and precise object detection.
Infrared (IR) Proximity Sensors
These are the simplest and cheapest types. An IR sensor continuously beams out infrared light. If an object gets close enough, the light bounces off it and is “seen” by a detector on the sensor. These are not good for measuring exact distances but are perfect for simple detection, such as in an automatic hand-soap dispenser or a robot that needs to know when it’s about to hit a wall.
The Connectivity (The “How it Talks”)
A sensor’s data is useless if it stays on the sensor. This is where communication protocols come in. You must differentiate the sensor (what measures) from the network (what transmits).
Why LoRaWAN is a Game-Changer
LoRaWAN (Long Range Wide Area Network) is not a sensor; it’s a radio technology that has revolutionised remote monitoring.
- What it is: A wireless protocol designed specifically for sending small packets of data over very long distances using very little power.
- The Benefits: A sensor (like an ultrasonic one) connected to a LoRaWAN transmitter can run for 5-10 years on a single battery. It can send its data (e.g., “Tank 70% full”) over several kilometres to a central gateway, even from deep inside a building or a rural field.
- Use Cases: This makes it perfect for smart bins, water tank monitoring, and flood alerts. The LoRa Alliance is the official body that standardises this powerful technology.
Other Communication Options
- Wi-Fi / Bluetooth: These are high-data, short-range, and high-power. They are great for smart home devices that are plugged into the wall, but a battery-powered sensor would be dead in a few days.
- Cellular (4G/NB-IoT): This is the main alternative to LoRaWAN. NB-IoT (Narrowband IoT) is a similar low-power technology that uses the existing mobile phone network. It’s a great choice, but it often comes with a higher subscription cost and may still use more power than LoRaWAN.
How to Select the Right Solution
Follow this three-step process to get the right device.
Step 1: Define Your Target and Environment
First, what are you measuring?
- Range: Do you need to measure 10cm or 100 metres?
- Target: Is it a solid (like a wall), a liquid (in a tank), or a dark/transparent object (which can be hard for IR/Laser)?
- Environment: Is it indoors, or outdoors in the rain, dust, or fog?
Step 2: Choose the Sensor Technology
Based on your answers, you can choose the sensor.
- Best for liquids in tanks: Ultrasonic.
- Best for long-range & high-accuracy: Laser (LiDAR/ToF).
- Best for simple, short-range detection: Infrared (IR).
Step 3: Choose Your Connectivity
Now, how will you get the data?
- Is it remote, outdoors, or battery-powered? LoRaWAN is almost certainly your best choice.
- Is it indoors, near a power socket, and needs to send lots of data (like video)? Wi-Fi is the better fit.
Real-World Applications
Tank Level Monitoring
Placing an ultrasonic sensor at the top of a water or fuel tank, connected to a LoRaWAN transmitter, allows a facilities manager to get daily updates on tank levels without ever leaving their desk.
Flood and Water Level Monitoring
Authorities can place LoRaWAN-enabled ultrasonic sensors in rivers, drains, and coastal areas. These devices can send an instant alert when water levels rise to a dangerous point, providing an early warning system to protect properties and lives. This proactive monitoring is a key part of modern community safety, complementing government advice on flood preparedness.
Conclusion
Choosing a distance sensor is a two-part decision. First, you must select the right sensing technology (like ultrasonic or laser) for your specific target and environment. Second, you must choose the right communication technology to get that data. For the growing world of remote, battery-powered monitoring, LoRaWAN has emerged as the clear winner, enabling sensors to operate for years while sending vital data from kilometres away.
