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Distance Measurement – Understand & Optimize#

Chapter goal

Goal: Understand how distance measurement works and learn which parameters optimize it.

Prerequisite

For this chapter the Radar Sensor Blob UI app on the CMTK is helpful. It is available in the App Store (installation info in the manual).

The Radar Sensor Blob UI also exists as a plugin for the Balluff Engineering Tool (BET). Plugins are shipped with the BET. Using BET you can connect Balluff IO-Link masters via Ethernet or USB.

Optimization is possible without visualization – you will simply miss raw data insights.

How it works#

Factory settings make the sensor determine the distance of the strongest target. Relevant parameters are listed below; their effect is described afterwards.

Parameter table
Parameter
Section
Parameter name		 Index
Subindex		 Default
Lower limit measurement range
Sensor Measurement Config
Measurement Range.Lower		 514
1		 300 mm
Upper limit measurement range
Sensor Measurement Config
Measurement Range.Upper		 514
2		 15000 mm
Target search mode
Radar Sensor Configuration
Target search mode		 271
2		 Strongest target
Minimum target search distance
Radar Sensor Configuration
Minimum distance for target search		 271
3		 150 mm
Maximum target search distance
Radar Sensor Configuration
Maximum distance for target search		 271
4		 15000 mm
Minimum target strength
Radar Sensor Configuration
Minimum target strength		 271
5		 3 dB
Averaging count
Radar Sensor Configuration
Number of averaging		 271
1		 10

Find the parameters in the CMTK under Parameters (IODD) → Parameters after selecting the sensor under Connected devices.

CMTK parameters

Parameter overview

You can ideally visualize their relationship with the Radar Sensor Blob UI. Open it under Radar sensor, refresh once with Update or enable Auto Update.

Radar Sensor Blob UI

Magnitude#

Magnitude (blue line) shows the reflection strength of an object at a certain distance. The higher the value, the stronger the reflection. See also Commissioning.

Target search mode, search window and minimum target strength#

In the standard mode Strongest target the sensor selects the highest magnitude peak within the search window (min/max target search distance; black rectangle). A target must also lie above the threshold (dashed red line = minimum target strength).

Important

The strongest value must be a pronounced peak (peak = central value with both neighbors smaller). The visualization shows rastered values. The computed value can lie slightly outside the search window although the peak visually still appears inside – in this case it is discarded.

Measurement range#

The measurement range splits into safe and unsafe portion. In the near range the sensor can detect objects but accuracy drops significantly (> ±10 mm). The effective limit depends on application, environment and target reflection. Unsafe values are signaled via LEDs (yellow blinking) and via process data.

Measurement range warning

Configuration#

Optimize distance measurement#

If multiple objects cause the wrong target to be chosen or values fluctuate strongly, you can adjust settings. The settings are under Radar Sensor Configuration. Typical workflow comprises four steps:

1. Configure search window#

Set min and max target search distance so irrelevant targets are excluded (values in mm).

Search window

2. Configure target search mode#

If the search window is insufficient, switch from Strongest target to Nearest target (first object above threshold).

Target search mode

3. Configure minimum target strength#

Increase or decrease minimum target strength to ignore weak targets or allow additional ones.

Minimum target strength

4. Configure averaging#

Adjust averaging (moving average of last n measurements) – more smoothing vs. reaction speed.

Averaging

Examples#

Configuration scenarios

In each example minimal configuration changes show how the respective object can be detected. Deviations from the defaults are highlighted in bold.

Example 1

Object Search window Target search mode Minimum target strength
1 300–15000 mm Nearest target 3 dB
2 300–15000 mm Strongest target 3 dB
3 6000–15000 mm Strongest target 3 dB

Example 2

Object Search window Target search mode Minimum target strength
1 300–15000 mm Strongest target 3 dB
2 2000–15000 mm Strongest target 3 dB
3 6000–15000 mm Strongest target 3 dB

Example 3

Object Search window Target search mode Minimum target strength
1 300–15000 mm Nearest target 3 dB
2 300–15000 mm Nearest target 12 dB
3 300–15000 mm Strongest target 3 dB

Example 4

Object Search window Target search mode Minimum target strength
1 300–15000 mm Strongest target 3 dB
2 2000–15000 mm Nearest target 3 dB
3 2000–15000 mm Strongest target 12 dB

Configure measurement offset#

If you mount the sensor further away (to bypass near‑range inaccuracy) you can set a measurement offset.

Parameter table
Parameter
Section
Parameter name		 Index
Subindex		 Default
Measurement offset
Sensor Measurement Config
Offset Distance		 193
0		 0 mm
Preset distance
Sensor Measurement Config
Preset Distance		 194
0		 0 mm
Teach Preset (Command)
Sensor Measurement Config
Standard Command		 2
0		 Teach Preset

Configure measurement offset

You can enter the offset manually (value is subtracted from measurement) or calculate it automatically.

Examples

Example 1: Measured value is currently 1.5 m but should be 1 m. Difference 500 mm. Enter 500 mm into Measurement offset.

Example 2: Measured value is currently 1.5 m but should be 2 m. Difference −500 mm. Enter −500 mm into Measurement offset.

For automatic configuration place the object at a defined position (e.g. 2 m), enter that value (2000 mm) into Preset distance and execute Teach Preset. The offset is set so the measured value afterwards is 2000 mm.