Ultrasonic Distance Sensor
Measures distance by timing an ultrasonic pulse echo — output is proportional to the target distance.
01 / Recognize it
What this sensor looks like
Learn the housing, active face, mounting, and connector before you meet it on a machine.
Hardware recognition
Know what to look for
Use the silhouette, active face, and connection style to identify the device before checking its part number and datasheet.
- Body and mounting
- Usually a cylindrical or rectangular housing with one or two round acoustic faces.
- Active face
- The transducer face must point squarely at the target and remain unobstructed.
- Cable and terminals
- An M12 connector or cable carries power and switching or analog output.
02 / Understand the principle
Watch cause become a PLC signal
Follow the physical event through the sensing element and into the exact controller value.
Signal story / live loop
Ultrasonic Distance Sensor: cause to controller
Now showingPhysical event
Liquid surface moves → Echo time changes → %IW72 = 2,600 mm
03 / Test and commission it
Commission it on the bench
Move the process, adjust the setpoint, invert the logic and inject faults. Watch the PLC value respond immediately.
Commissioning bench
Ultrasonic Distance Sensor
PLC channel
%IW72
RAW 9677
Engineering value
1400 mm
Measured distance
Channel healthy
Signal is inside the expected operating range
Commissioning note: Keep the target outside the blind zone and avoid angled surfaces that deflect the echo.
Field guide
An ultrasonic sensor measures distance by emitting a burst of high-frequency sound (40-400 kHz, above the range of human hearing) and measuring the time it takes for the echo to return from a target surface. Since the speed of sound in air is approximately 343 m/s, the round-trip time divided by two gives the distance: distance = (time × speed_of_sound) / 2.
The sensor has a blind zone — a minimum distance near the face where the echo returns before the transmitter has switched to receive mode. Typical blind zones are 30-300 mm depending on the model. Targets closer than the blind zone are not detected reliably.
The beam width is another key specification. Wide beams average the return from a larger area, which can give misleading readings when a target has an irregular or angled surface. Narrow-beam models (pencil-beam) are used for precise measurement of irregular objects.
Output options include 4-20 mA (proportional to distance), 0-10 V, or discrete switching (when the target enters a set window). Most modern sensors also offer IO-Link for digital configuration without changing the wiring.
Temperature affects the speed of sound (it increases with temperature by about 0.6 m/s per °C). Premium sensors include a temperature compensation circuit; budget models require an ambient temperature correction factor in the PLC scaling.
Use this when…
- Measuring fill level in a tank without contacting the liquid
- Detecting pallet height or stack level on a conveyor
- Providing distance feedback for a robotic arm or gantry
Where you will see it
Silo level
Ultrasonic sensors mounted at the top of grain silos measure the distance to the grain surface, giving continuous volumetric fill level.
Web tension
Ultrasonic sensors on dancer rollers measure displacement, feeding a PLC PID block that controls unwind brake torque.
Next skill
Connect it to PLC logic
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