Ultrasonic Sensor Technical Information

OMRONCONFIDENTIAL

Version 1 Jan 07

1. What is Ultrasonic sensor?2. Omron’s Range of Ultrasonic Sensors3. Ultrasonic Sensor Terminologies4. Application Examples5. Guidelines for selection of Ultrasonic Sensor

Topics

The ultrasonic sensor generates sound wave and measures the time of flight of this wave from sensor to and from the object and calculates the distance to the target. A simple teach-in setting defines the distance at which the sensor will switch.

Sensing performance is not affected by object color, surface and texture.

objectTransmitter

Receiver

Sound waves

1. What is Ultrasonic Sensor?

Dead ZoneDistance between the sensing face and the minimum sensing range.

Dead zone

Ultrasonic sensor Sensing zone

Tone Burst

If object is too near to the sensor (within the dead zone), the tone burst leading edge can strike the target and return in echo to the sensor before the trailing edge left the transducer. The echo generated can reflect off the face of the sensor and goes back to the target. This multiple echo can cause error.

1. What is Ultrasonic Sensor?

Background suppressionUltrasonic sensor measures the elapsed time from the sensor to the target object and back from it. When the sensor is adjusted to sense the object at a given distance, a timing window is established. The sensor accepts and acknowledge the echoes received within the window. Signal echoing from background materials will not trigger the sensor.

Ultrasonic sensor

t= 50ms

Background

Object

T= 80msThe sensor recognizes that the timing for the echoes is longer than expected and will not trigger an output.

1. What is Ultrasonic Sensor?

Factors that affect sensing distance: Object Material Object Size

Size of flat target

Sensing Distance

Cardboard

Sponge

Metal

3X3 12X12 50X50

10%

30%

55%

75%

Sponge absorb most of the sound wave, therefore the sensing distance is the shorter. The bigger the object, the longer is the sensing distance.

1. What is Ultrasonic Sensor?

1. E4C-UDA - Digital Amplifier Ultrasonic Sensor 3 types of sensor heads with different sensing distance to choose from (30cm, 80cm or 100cm) Amplifier is available in twin output and analog output models Almost straight directional pattern

2. Omron’s Range of Ultrasonic SensorsLatest

2. E4DA - Ultrasonic Displacement Sensor Sensing distance from 30 to 70mm High speed response of 2ms High resolution of 0.2mm Enables the detection of minute object Hold function eliminates chattering

3. E4PA-N - Ultrasonic Displacement Sensor (long sensing distance) Sensing distance from 50 to 6000mm Long sensing distance suits a variety of applications A setting plug with temperature compensation function makes setting of

measurement range easy Equipped with new mutual interference prevention function

4. E4E2 - Compact Ultrasonic Sensor Sensing distance till 500mm Ideal for detecting transparent film, transparent bottles and clear plastic

containers Compact, vertical design with built-in amplifier allows easy mounting on small

conveyor lines Sensing distance = 500mm Equipped with stability indicator

5. E4B - Ultrasonic Proximity Sensor Available in through-beam & diffuse-reflective models Sensing distance zone setting for the ultrasonic beam (1m for through-beam & up

till 700mm for diffuse-reflective) Stable detection of a variety of objects regardless of color, transparency, or

material (metallic/non-metallic) of objects Narrow ultrasonic beam width of 8°, enables minute object detection (as small as

20 x 20mm) Detects objects smoothly while largely suppressing interference from background

objects

2. Omron’s Range of Ultrasonic Sensors

2. Omron’s Range of Ultrasonic Sensors6. E4C - Ultrasonic Proximity Sensor

Available in through-beam (500mm) & diffuse-reflective models (100 to 350mm)

Stable detection of a variety of objects regardless of color, transparency, or material (metallic or non-metallic) of objects

Separate amplifier design allows sensor head to be compact as M18 Reflective models with limited sensing zones ensure smooth object detection

without being influenced by background objects Incorporates a sync selector to prevent mutual interference

7. E4B - Ultrasonic Proximity Sensor Sensing distance zone setting for the ultrasonic beam Stable detection of a variety of objects regardless of color, transparency, or

material (metallic/non-metallic) of objects Narrow ultrasonic beam width of 8°, enables minute object detection (as

small as 20 x 20mm) Detects objects smoothly while largely suppressing interference from

background objects

3. Ultrasonic Sensor TerminologiesTerms ExplanationDirectional Characteristics

The ratio of the sound output (needed to transmit the specified sound energy to the targeted object) of the non-directivity transmitter to the sound output of the directivity transmitter is called the directivity gain.As the frequency and vibration area increase, the directivity grows sharper and sound waves are emitted with greater efficiency.The directivity of a sensor unit used as an ultrasonic switch is 8° to 30° (sound pressure half-angle).The directivity is also strongly affected by the shape of the sensor horn and the vibration mode of the transducer, and thus the sensor unit shape, operation frequency, and transducer type are selected to provide the desired operation range.

F.S (Full Scale) This indicates the range of the rated detection distance. Each model has a different value.

Limit Zone(Reflective Models)

Not only the maximum detection distance but also the minimum detection distance can be adjusted, in connection with or independently of the maximum distance. This detection range is called the limit zone (zone limit).

3. Ultrasonic Sensor TerminologiesTerms ExplanationLinearity When the relation between the distance and the linear output at fixed temperature

and voltage conditions is shown as a graph, this is the percentage of the maximum error with respect to an ideal straight line.

Multi-reflection This occurs when ultrasonic waves that have already reflected from the detection object once reflect from the sensor head surface, nearby walls, or the ceiling back to the detection object, and then back to the sensor.For e.g. in the case of double reflection, the same ultrasound waves are received as a single reflection but at twice the distance.

Non-sensitive zone & Uncertainty zone (Reflective models)

The non-sensitive zone is the interval between the surface of the sensor head and the minimum detection distance resulting from detection distance adjustment. The uncertainty zone is the area close to the sensor head configuration and reverberations.Detection may occur in the uncertainty zone due to multi-reflection between the sensor and the object.

Received Waves Transmitted ultrasound waves that are received at the transducer, and which are either direct or reflected from an object. Normally expressed as a converted voltage, or as a sound pressure.

3. Ultrasonic Sensor TerminologiesTerms ExplanationReflection & Transmission

Ultrasound waves move straight forward in a uniform medium, and are reflected and transmitted at the boundary between differing media. This phenomenon is affected by the type and shape of the media. A human body in air causes considerable reflection and can be easily detected.

Side Lobe Directivity is indicated using a graph showing the sound level as a length from the center as the angle is shifted away from the angle of the transducer center, where the sound level (sound strength) is a maximum. As the angle increases from the center, the directivity decreases, and then after a certain point increases.This is called the side lobe, and can result in stray reflection off peripheral objects that will affect the detection characteristics.

Speed of Sound The speed of sound "C" in air is C ≈ 331.5 + 0.61 θ (m/s), where θ is the air temperature (°C). The speed of sound changes as the air temperature changes, and this results in temperature-based distance measurement error.

Transducer This is a device which uses electrical energy to generate ultrasonic waves, and which also converts ultrasonic vibrational energy

Transmitted Waves Ultrasound waves that are emitted in the specified direction when the transducer is connected to the oscillator. Normally expressed as a voltage applied to the transducer, or as a sound pressure.

4. Application Examples

Detection of Transparent LCD Substrate Detection of Position of Remaining Glass Substrates in Cassettes

Detection of Thin, Clear Film Detection of Transparent Tray

4. Application Examples

Detection of Tires Detection of Liquid Level

Control of Rubber Sheet Tension Detection of Sheet Sag

5. Guidelines for Selection of Ultrasonic Sensor

1. Sensing Method Through-beam => E4E2, E4C, E4B-T

Reflective => E4B-LS/RS, E4C-LS, E4PA-N

2. Sensing Distance

(Longest up till 6metres => E4PA-N)

3. Directional Characteristics

(Straight directional pattern => E4C-UDA Series)

4. Built-in Amplifier / Separate Amplifier Built-in Amplifier => E4E2, E4B, E4PA-N

Separate Amplifier => E4C, E4C-UDA

5. Output Configuration

NPN/PNP Open Collector Configuration, Terminal Selection

Current / Voltage Output

6. Response Frequency