ITLE20010007A1 - ULTRASONIC LEVEL SENSOR. - Google Patents

Description

Ultrasonic level sensor - Instrument for measuring the level of liquids through the use of ultrasound compatible with multiple indicator instruments.

-State of the art

Currently there are systems of continuous detection of the liquid level operating on various principles:

1) when the resistance is changed mechanically:

1. yes with slider moved by float 2. both with magnetically actuated electrical contacts

2) with pressure variation

3) by microwave

4) by use of ultrasounds but require an external power supply and are compatible with a single indicator instrument.

5) by vibration.

Summary

The various electronic circuits that make up the system operate as follows: they activate an ultrasonic capsule and process the return echo, picked up by u: ultrasound microphone, determine the time taken by the signal in the path between the two transducers and then calculate the distance from the liquids such as half of that path. They determine the signal to be sent to the indicator instrument for the correct positioning of its index, in proportion to the liquid present and according to the type of instrument connected. They obtain the power supply voltage from the display instrument.

The system is also equipped with a programming unit capable of adapting the sensor to any (up to 2500mm) and any tank

indicator that operates on the principle of variation of resistance.

DESCRIPTION OF THE OPERATION OF THE INDICATOR INSTRUMENT. (See Fig: l Annex 1)

The indicator instrument is made with two coils arranged at 90 degrees and a magnetic needle.

The sensor is applied between the S and GND terminals, while battery power is supplied from the and GND terminals. The change in resistance of the sensor modifies the field produced by the coils and allows the index to move as desired.

- Description of the invention and Tables

The system consists of (See Fig: 2, Annex 1): two ultrasonic elements, i.e. a transmitter (1) and receiver (2), a micro-controller (3), a temperature probe (4), an amplifier circuit- squarer (5) and an interface circuit (6) with the indicator instrument (7).

The transducers are covered with liquid-tight material but transparent to ultrasound.

PRINCIPLE OF OPERATION The operation of the sensor is based on the time taken by an acoustic wave to travel a round trip in an environment of the type indicated in figure 3 in Annex 1.

The pulse emitted by the transducer (TX) is reflected from the liquid surface following the path (1) and returns to the sensor (RX), following the path (2) and taking a time T.

By measuring this time and knowing the velocity V and the depth of the tank Pr, the height of the liquid is determined as follows:

1)

2) Pi

TO INDICATE

The CONTROL CIRCUIT, using this result, sends to the indicator instrument a signal eg o proportional to allow the correct positioning of its index.

The signal sent to the instrument is of the ON-OFF type, the modulation of the on and off times determines the position of the index. In the OFF period, the voltage across the instrument is used to charge a capacitor capable of powering the electronics in the ON period.

Description of the functions performed by the various blocks of the level sensor:

(See Fig. 2, Annex 1)

1) The interface circuit (6) has the task of obtaining the power supply of the electronics and of moving the index of the indicator instrument.

2) The micro-controller (3) has the task of activating the transmitter (1), determining the time taken by the return echo, calculating the level and then setting the instrument index in proportion to the liquid present, according to the programmed parameters.

3) The transmitter (1) transforms the electrical signal sent by the micro-controller into ultrasonic pressure.

4) The receiver (2) transforms the return echo into an electrical signal.

5) The amplifier-squarer circuit (5) modifies the signal to adapt it to the levels required by the micro-controller (3).

6) The temperature probe (optional) (4) has the task of detecting the ambient temperature to allow the micro-controller to appropriately correct the calculations according to the different signal propagation speed.

Attachment 1, Fig. 4, shows the electrical diagram of the sensor, and Fig. 5, shows the diagram of the programmer.

DETERMINATION OF THE DEPTH OF THE TANK (self-calibration)

Using sensors with a high working frequency it is possible to make the instrument self-calibrating as it is also able to detect the echo coming from the bottom of the tank (See Fig. 5, Annex 1):

The impulse emitted by the transducer is reflected for the first time by the liquid surface following the path (1) and returns to the sensor after a time: t1. After t2, there is a second pulse, reflected from the bottom, which returns to the sensor.

By measuring these times and knowing the two speeds Va and VI, the height of the liquid can be determined:

Claims (8)

- Claims 1) Compatible with all indicator instruments that operate on the principle of variation of resistance. 2) Connection à "two wires", therefore, compatible with all systems as it is powered by the indicator instrument itself. 3) Possibility of working in an environment with risk of explosion. 4) Adaptable to all tanks up to 2500mm. 5) Not attackable by hydrocarbons and sea water. 6) Absence of moving parts. 7) Small size. 8) Programmable from the outside or self-programmable for the recognition of the depth of the tank