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Frequently Asked Questions

What is an Ultrasonic level sensor?

Ultrasonic sensors use sound waves to measure distance. A sensor would normally be mounted at the top of a tank and direct a sound wave down towards the surface of the product. When the sound wave hits the product it is reflected and returned to the sensor.

How ultrasonic Distance or level sensors work?

Ultrasonic sensors emit a sound pulse that reflects off of objects entering the wave field. The reflected sound, or “echo” is then received by the sensor. AG Electronics
Ultrasonic sensing technology is based on the principle that sound has a relatively constant velocity. The time for an ultrasonic sensor’s beam to strike the target and return is directly proportional to the distance to the object. Consequently, ultrasonic sensors are used frequently for distance measurement applications such as level control.

Ultrasonic sensors are capable of detecting most objects — metal or non- metal, clear or opaque, liquid, solid, or granular — that have sufficient acoustic reflectivity. Another advantage of ultrasonic sensors is that they are less affected by condensing moisture than photoelectric sensors.

A downside to ultrasonic sensors is that sound absorbing materials, such as cloth, soft rubber, flour and foam, make poor target objects.

What affects the range of sensor?

In Liquid A) Side walls of tank, B) Agitator of stirrer in the tank, installation in tall fittings with narrow risers.. C) Extreme foam, vapour, turbulence can absorb and/or deflect away a substantial portion of the return signal. D) Surface temperature

In Solid A) size of the object. B) Angle of the object. C) surface smoothness D) Surface temperature

What is the relationship between temperature and speed of sound?

The higher the temperature the faster the speed of sound. For example, 344 m/s @ 20°C and 349 m/s @ 30°C. The error in the speed of sound related to temperature is 0,17% per °C. This temperature change is compensated for with a built in thermistor on the face of all AGEcho Ultrasonic sensors.

What influence does temperature have on the measuring result?

The running time of the sonic impulse, which is used to determine the distance i.e. the filling level, is directly dependent on the temperature of the gas above the product to be measured. For this reason, every ultrasonic device has an integrated temperature sensor, which enables compensation of the temperature influence.

What is the so-called Blind zone / Dead band of ultrasonic sensors?

Ultrasonic proximity sensors have a small unusable area near the face of the sensor. If the ultrasonic beam leaves the sensor, strikes the target, and returns before the sensor has completed its transmission, the sensor is unable to receive the echo accurately. This unusable area is known as the blind zone or Dead band. AG Electronics
The dead band is the area in front of the electroacoustic Ultrasonic sensor of ultrasonic sensors, in which measurement is not possible. Basically, it represents the time (converted into a distance) which is needed to emit the sending impulse and then activate the receiver.

How it is use for counting and sorting objects?

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Distance measurement, height measurement, or work piece positioning

How can I use more than one Ultrasonic level sensor in the same system?

Spacing between sensors is determined by their beam angles. The sensors must be spaced so they do not interfere with each other. This interference is sometimes called “crosstalk.” AG Electronics
Spacing of Ultrasonic Sensors

Is the range of sensor is depend on size and angle of object?

Yes. The range is given for particular size (1 meter X 2 meter) which should be kept perpendicular to the sensor. They require the transducer face be within 3° of parallel to smooth, flat target objects. AG Electronics
Smooth flat targets require precise sensor alignment

What factor affects the Maximum Sensing Distance of the ultrasonic sensor?

Target size and material determine the maximum distance at which the sensor is capable of seeing the object. The harder an object is to detect, the shorter the maximum sensing distance can be.

Materials that absorb sound — foam, cotton, rubber, etc. — are more difficult to detect than acoustically reflective materials, like steel, plastic, or glass. If detected at all, these absorbent materials can limit maximum sensing distance. AG Electronics
Sensing range with maximum sensitivity

If power is lost, will the ultrasonic level sensor loose its configuration?

No, the sensors have non-volatile memory.

How do I select the best ultrasonic level sensor range for optimum performance?

Select a sensor range that covers the tank height with at least 25% margin. In challenging applications with light foam, vapor and/or turbulence, select a sensor range that is double the tank height. The additional sensor will improve performance in such conditions.

How do I identify the best mounting location for my ultrasonic level sensor?

The sensor should be located so that the acoustic signal path is free of obstructions from side-walls, ladders, pipes, mixers and other instruments. The sensor should be mounted level and/or perpendicular to the liquid surface.

If substantial foam, vapor and/or turbulence are present, install the sensor in a stand-pipe.

What are the exposed materials of the Ultrasonic level sensor and what use is it rated for?

The outdoor sensor line is IP67 rated for water and dust intrusion. This material list allows customers to determine if the part will meet their specific requirements. The sensor and related IP67 products have exposed materials. The list of these materials is Aluminum (covering the Ultrasonic sensor), PVC (the housing material), and Silicone Rubber. Our standard products use Silicon O-Rings for general purpose sealing. The O-Rings are for even more robust sealing in many.

What are the advantages of sensor manufacture in India?

a) Lowest cost
b) Timely delivery
c) Full technical support
d) No restriction in quantity
e) Saves foreign exchange, improve the Indian economy.

Which products can be measured with ultrasound?

The filling levels of almost all products can be measured with ultrasonic sensors. As long as liquids or bulk materials reflect the sound wave sufficiently, measurement is possible. However, the temperature, pressure and composition of the gas above the measured product have significant influence on the measurement! Ultrasound sensors are also limited in their area of application due to the implemented (mostly synthetic) constructive materials.

Can the sensors measure correctly in lime applications?

Lime applications are challenging application to ultrasonic sensors and in many cases cannot measure during filling process due to high dust presence.

Is it possible to measure PVC granulates?

Static discharge produced by the PVC granulates may affect the ultrasonic signal and interfere with the measurement.

Is it possible to measure in Gravel/ Barley/Grain/Soya and similar applications?

Yes, but High dust density may interfere with the measurement, especially during filling time.

Can we use sensor at temperature level above 70º C?

The sensor cannot work above the temperature range 0º -70º C.

What does the 4-20 mA signals represent?

The 4-20 mA represents the sensor's measurement span. The 20 mA set point is normally placed near the bottom of the empty tank, or the greatest measurement distance from the sensor. The 4 mA set point is normally placed near the top of the full tank, or the shortest measurement distance from the sensor. The sensor will proportionately generate a 20 mA signal when the tank is empty and a 4 mA signal when the tank is full.

Can I reverse the measurement span from 4-20 mA to 20-4 mA?

Yes, the sensor can be configured such that the 20 mA set point is empty and the 4 mA set point is full.

What is the maximum 4-20 mA signal distance form sensor to the controller?

The sensor can be installed up to 300 meters from its point of termination using a shielded, 18-20 gauge twisted pair cable and 12 VDC power supply. The total loop resistance should not exceed 900 ohms.

What are the benefits of 4-20 mA signals?

Analog 4-20 mA signals have the following advantages: The same two-wires carry both the sensor power and signal; 4-20 mA is easily converted to a 1-5 VDC input via a 250 Ohm Watt resistor or 1-10 VDC input via a 500 Ohm Watt resistor; 4-20 mA is low current and therefore has a low heating loss through the signal wire; and with shielded cable, 4-20 mA is noise resistant to radiated and inducted interference.

Can we place a loop powered level indicator in series with the 4-20 mA signals?

Yes, as long as the total loop resistance is less than 900 Ohms.
Protective Measures
In wet applications, the sensor should not be mounted in such a way that standing water or other fluids can rest on the sensing face. In general, to maintain operating efficiency, care must be taken to prevent solid or liquid deposits from forming on the sensor face.
The sensor’s face can also be vulnerable to aggressive acid or alkaline atmospheres.
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