1

The Factory Automation

Sensor Handbook
Proximity Sensors – The Basics

1 Detecting Height
Differences

2 Positioning

3 Detecting the Presence/

Absence of Holes

Expert Advice and Troubleshooting Guide for Selecting Proximity Sensors

 Expert Advice and Troubleshooting Guide for Selecting Proximity Sensors

1. Detecting Height Differences

Typical Application

Detecting overlapping thin targets

Tips
Calculate the capability for detecting minute
height differences based on the catalog
specifications:
[Hysteresis] < Detectable height difference
When temperature fluctuations exist:
[Hysteresis + Temperature fluctuation]
< Detectable height difference

Advantages of the separate-amplifier type over the built-in amplifier type for height
difference detection
■ Self-contained type and amplifier-in-cable type:
The sensitivity and hysteresis are fixed within a certain range allowing for a margin of variation.
Detection of height differences is available when the temperature drift is taken into account. (Please
note that this type is not best suited for demanding detection of minute height differences.)
■ Separate amplifier type:
The variable sensitivity allows you to adjust the sensitivity. Stable detecting operation is expected for
more demanding detection of minute height differences.
Hysteresis Temperature fluctuation
Reset distance Hysteresis refers to the
absolute value of the
Detecting difference between the
distance detecting distance
(distance from the
detecting surface to the
Hysteresis operating point) and the After a
reset distance (distance negative shift
Operating distance The target cannot be detected.
Operating Return from the detecting
point (ON) point (OFF) surface of a sensor head Temperature fluctuation refers to the effect of ambient
to the reset point). temperature within the rated operating range on the detecting
distance of a sensor. Expressed as the percentage of change
from the operating distance obtained at a temperature of +23°C.
Example
What is the detectable height difference for the EH-308 with a detecting distance of 1.0 mm?
Specifications: EH-308 + ES-M1
Temperature fluctuation of the sensor head Temperature fluctuation of the amplifier (ES)
Hysteresis
(-10 to + 60°C) (0 to + 50°C)
0.04 mm ±10% of detecting distance at +23°C ±8% of detecting distance at +23°C
(The temperature fluctuation with a detecting distance of 1 mm)
• EH-308: Detecting distance 1.0 mm x temperature fluctuation ±10% = ± 0.1 mm
(In detecting the height differences, the deviance for the negative direction will be ignored.)*1
• Amplifier (ES): Detecting distance 1.0 mm x temperature fluctuation ±8% = ± 0.08 mm
(In detecting the height differences, the deviance for the negative direction will be ignored.)*1
Therefore, the minimum detectable height difference will be:
0.04 (hysteresis)+0.1 (temperature fluctuation)+0.08 (temperature fluctuation of the amplifier)=0.22*2
*1. Refer to “About temperature fluctuation” above.
*2. Height differences smaller than 0.22 mm may be detectable. The calculation is based on the worst conditions of the specification values.
 Technical Data

Secrets for stable detection of minute height differences

✰ The smaller the setting distance, the better the detection stability.
Reason The hysteresis becomes smaller as the distance becomes smaller, resulting in a greater
capability for height difference detection.
✰ The longer the stable detecting distance, the better the detection stability.
Reason The hysteresis becomes to half the original value when it is set at half the stable
detecting distance or shorter.

[Hysteresis Data]
Without temperature fluctuation (Typical)
Environment: 23°C constant
Target: Iron plate for the ES, and aluminum plate for the ET
Units: mm
Sensor head EH-303A EH-308 EH-614A ET-305 ET-110
(Stable detecting distance) (0.8 mm) (2 mm) (5 mm) (1 mm) (2 mm)
1 0.050 0.040 0.050 0.010 0.010
Hysteresis at 1, 1/2, 1/4
of the stable detecting 1/2 0.020 0.020 0.018 0.005 0.005
distance
1/4 0.014 0.016 0.012 0.002 0.002

Hint The detectable height difference in an environment where temperature fluctuation (ES: -10 to +
60°C, ET: 0 to 50°C) applies for the sensor head will be as follows: ES: up to 10% max. of
detecting distance, ET: up to 20% max. of detecting distance. (Some EH models excluded.)
Hysteresis Theoretical Values

With temperature fluctuation (Typical)

Environment: Variable within the range of - 10 to + 60°C (ES) and 0 to 50°C
Target: Iron plate for the ES, and aluminum plate for the ET
Units: mm
Sensor head EH-303A EH-308 EH-614A ET-305 ET-110
(Stable detecting distance) (0.8 mm) (2 mm) (5 mm) (1 mm) (2 mm)
1 0.130 0.240 0.550 0.210 0.410
Hysteresis at 1, 1/2, 1/4
of the stable detecting 1/2 0.060 0.120 0.268 0.105 0.205
distance
1/4 0.034 0.066 0.137 0.052 0.102

* When temperature fluctuation is applied to the amplifier, 8% of the detecting distance will be added.
Example: When performing detection with the EH-614A at a distance from the target of 2.5 mm, the
detectable height difference will be 0.268 + 2.5 x 0.08 = 0.468 mm.
 Expert Advice and Troubleshooting Guide for Selecting Proximity Sensors

2. Positioning
Typical Application

Positioning of a workpiece
Tips
For the positioning accuracy, refer to “Repeatability
(The ES Series)” in the catalog specifications.

Definition of repeatability
ON
ON

Standard
detecting
target

Tolerance range

Repeatability indicates the tolerance range of the

detecting position when a standard target is
subject to repeated detection under set conditions.

Detection method for ensuring high accuracy of “Repeatability”

When a target approaches the sensor When a target approaches the sensor
head in a perpendicular direction: head in a horizontal direction:

Standard target Direction of

for detection movement of L/4
the target Standard target
for detection
Stable detecting
distance 1/2 of the stable
detecting distance Direction of
movement of
the target
L

Adjust the sensor to be turned ON precisely Adjust the sensor to be turned ON precisely
within the stable detecting distance according to the example illustrated above.
illustrated above.
 Technical Data

(Typical) Units: mm
Sensor head EH-303A EH-305 EH-108 EH-614A EH-402

Maximum tolerance 0.003 0.002 0.004 0.004 0.002

Maximum tolerance: The maximum deviation between the detecting distances with the ON position at
the first detection as “0”.

Measurement Method
Use the standard target for each sensor head and adjust the sensitivity so that the ON is triggered when
1/4 of the sensor head is covered at 1/2 of the stable detecting distance. Measure the errors between
the ON positions when the target repeatedly approaches from the same direction.

1/2 of the stable detecting

distance (mm) Standard target

Hint Generally, the repeatability of positioning in the horizontal direction is lower compared with
positioning in the perpendicular direction. However, if detection is performed with the recom-
mended setting procedure(*), it is possible to obtain repeatability close to the data for
perpendicular positioning listed in the catalog. The effect of temperature fluctuations will be
reduced as well.
At the set sensitivity, the shorter the detecting distance, the lower the effect of temperature
fluctuations.

* Sensitivity adjustment at which the sensor is ON when 1/4 of the sensor head is covered at
1/2 of the stable detecting distance.
 Expert Advice and Troubleshooting Guide for Selecting Proximity Sensors

3. Detecting the Presence/Absence of Holes

Typical Application

Detecting the presence/absence of an eyelet

The structure of the proximity sensor and the magnetic field

The proximity sensor, which is called a high frequency oscillation type, generates a magnetic field
ahead of the sensor head. The operating principles of the EV Series and ET Series are different;
however, both types detect the change in the magnetic field caused by the target.
* The EV Series detects the stop of oscillation. The ET Series detects the attenuation of
oscillation.

Shielded type Non-shielded type

The side face of the sensing coil is The side face of the sensing coil is not metal-
encased in a metal shielding. shielded. This type provides a longer detecting
Can be embedded in a metal base. distance compared to the shielded type.
However, special cautions must be taken for
the mounting position, since this type is easily
affected by surrounding metal.

When the aperture of the hole is not large enough for releasing the magnetic field generation, the
detection may fail.

Make sure that the hole is larger than the outer diameter of the sensor head when performing
detection of eyelets.
 Technical Data

Secrets for detecting smaller eyelets

✰ Choose the shielded type.
Reason Smaller magnetic field is better suited for smaller eyelet detection compared to the non-
shielded type.

✰ The smaller the sensor head, the better the detection accuracy.
Reason The smaller the head diameter, the smaller the magnetic field.

✰ Perform detection within a stable detecting distance.

Reason To achieve stable detection (with separate amplifier model).

The smallest hole for stable detection:

Shielded type: Size of outer diameter or greater.
Non-shielded type: Three times the size of outer diameter or greater.

[Actual measurement of hole-detection (Typical)]

Environment: 23°C constant
Target: Iron plate for the ES, and aluminum plate for the ET
Units: mm
Sensor head EV-118M EV-118U EM-005 EH-308 ET-110
(Stable detecting distance) (5.0 mm) (10 mm) (1.0 mm) (2.0 mm) (2.0 mm)
Hysteresis at 1, 1/2, 1/4 1 ø18 ø54 ø5 ø8 ø10
of the stable detecting
distance 1/2 ø18 ø54 ø5 ø8 ø10

The spread of the magnetic field of the sensor in hole-detection

Target Target
Oscillating magnetic field Oscillating magnetic field

Hole
Hole
Coil Coil

The hole should be as large as the head diameter for releasing the magnetic field even if a hole
smaller than the diameter of the sensor head can be detected, because the sensing coil is wound to
nearly the same size as the sensor head diameter. Detection of holes smaller than the head
diameter may result in unstable operation (chattering, etc.).
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