RU2126957C1 - Level position pickup - Google Patents

Abstract

FIELD: check of level of liquid in technological vessels. SUBSTANCE: sensitive element of level position pickup is connected to converter by means of rod and is made up of excitation and test piezoelements placed into streamlined case of insulating material that transmits acoustic vibrations and is resistant to corrosive liquids and coat having low adhesion properties. Excitation and test piezoelements are mechanically tied to case with the use of elements conducting acoustic vibrations and are electrically interconnected through amplifier and band-pass filter to form circuit exciting ultrasonic vibrations. Determination of level position of liquid is based on difference of capabilities of liquids and gases to absorb energy of ultrasonic vibrations. EFFECT: improved operational characteristics. 1 cl, 2 dwg

Description

 The invention relates to instrumentation, and in particular to devices for controlling the level of liquid in technological vessels.

 Known acoustic level switch [1], which uses an acoustically coupled telephone emitter and microphone, an amplifier with a tuning resistor in its feedback circuit. In this case, the microphone is connected to the input of the amplifier, and an electromagnetic relay and an adjustment resistor are connected in series to its output. The use of this detector can lead to false alarms when measuring the level of liquids such as oil, fuel oil due to contamination of the telephone emitter and microphone and because of their icing when measured in difficult climatic conditions.

 Also known is a level position sensor, selected as a prototype [2], containing a sensitive element (SE), including a piezoelectric emitter and a receiver located in the housing and connected to the transducer.

 The described sensor has certain advantages: it is independent of density, unlike discrete level gauges.

 However, the applicability of the sensor is limited. So, for example, when using oil, fuel oil, oil products for monitoring, the constant viscous components present in them (paraffins, bitumen) can lead to contamination of the sensitive element, which can cause false alarms of the sensor. When used in certain temperature conditions, icing of the SE is also possible, which can also cause a false positive.

 The task of the invention is to increase the operational characteristics of the sensor.

 This object is achieved by the fact that in the level position sensor containing the sensing element connected to the rod transducer, as well as the mounting unit, the sensing element is made of piezoelectric elements of excitation and control placed in a streamlined body of insulating material that conducts sound vibrations and is resistant to aggressive liquids, while the piezoelectric elements of excitation and control are mechanically connected to the housing by sound-conducting elements and are electrically connected through an amplifier and a band-pass filter, forming an excitation circuit of ultrasonic vibrations.

 In this case, the housing of the sensitive element is proposed to be made of an insulating material that conducts sound vibrations and is resistant to aggressive fluids, and coatings with low adhesive properties.

 The determination of the position of the liquid level is based on the difference in the ability of the liquid and gases to absorb the energy of ultrasonic vibrations excited in the excitation circuit of two piezoelectric elements, a housing and an oscillation excitation generator. While the SE of the sensor is in the gas medium, the ultrasonic vibrations in its housing are practically not absorbed by the external environment. When the liquid level is higher than the sensitive element, the amplitude of ultrasonic vibrations in its body decreases.

The invention is illustrated by drawings, which show a specific embodiment of the sensor:
in FIG. 1 - design of the proposed liquid level sensor;
in FIG. 2 is a functional diagram of a sensor.

 The level sensor (see Fig. 1) contains a sensing element 1 made of a piezoelectric element 2 and a piezoelectric control 3 placed in a streamlined body 4. The sensing element rod 5 is connected to the transducer 6, and is also equipped with a mounting unit, which in the proposed embodiment is made in the form of a transition sleeve 7.

 In FIG. 2, as already noted, the functional diagram of the sensor is presented, which includes the piezoelectric excitation element 2 and the control piezoelectric element 3 connected through the preamplifier 8 and the bandpass filter 9, which form the ultrasonic vibrations excitation circuit, with the piezoelectric element 2. The piezoelectric control element 3 is connected also with a series-connected detector 10, a comparator 11 and a current switch 12.

 Piezoelectric elements 2 and 3 of the sensing element 1 are placed in the housing 4 from a material resistant to aggressive liquids and having insulating properties, which can be selected stainless steel, for example, grade 12X18H10E, because it conducts sound vibrations well and meets all the requirements for the material for the proposed design. At the same time, it is proposed to protect the housing of the sensitive element with an additional fluoroplastic coating, since it has low adhesive properties and will further reduce the contamination and icing of CE.

 CE 1 with a rod 5, also made of stainless steel, as a material resistant to aggressive liquids, with a fluoroplastic coating, connected to the transducer 6. The transducer 6 is proposed to be constructed in the form of an electronic circuit board located in a molded rectangular case made of aluminum alloy. It is proposed to equip the transmitter housing with a gland with a transition nut for docking a pipe or metal hose. The converter board is connected with a terminal connector for connecting the connecting cable. The sensor is installed on the threaded fitting of the adapter sleeve 7.

 Consider the operation of the sensor.

 The principle of operation of the sensor is based on measuring the degree of attenuation of ultrasonic vibrations excited in the sensing element. The piezoelectric elements of excitation 2 and control 3 with a preamplifier 8 and a band-pass filter 9 form a circuit in which oscillations of the ultrasonic frequency are excited. Ultrasonic vibrations in the housing 4 are transmitted to the control element 3.

 While the sensor 1 is in a gas environment, ultrasonic vibrations in its body are practically not absorbed by the external environment. When the SE 1 is immersed in a liquid, the energy of ultrasonic vibrations is absorbed by the liquid and the amplitude of the oscillations at the input of the preliminary amplifier 8 decreases. The amplitude of the oscillations is read by the detector 10 and controlled by the comparator 11. The comparator 11 closes the current switch 12, which was open in the absence of fluid around the sensing element 1.

 The large difference in the level of the useful signal at the dry / flooded sensor positions makes the device insensitive to possible contamination.

 The proposed sensor design can significantly improve its operational characteristics, as decreases the possibility of icing of SE and pollution by viscous components constantly present in a number of controlled liquids, such as, for example, oil, fuel oil, oil products with a high content of paraffins, bitumen. But even with a layer of ice or dirt a few millimeters thick, false alarms of the sensor will not occur, because CE piezoelectric elements are protected.

Literature:
1. RU, patent 2029921, G 01 F 23/28.

 2. EP, application 0409458, G 01 F 23/28, 01/23/91.

Claims (2)

 1. The level sensor containing a sensing element made of piezoelectric elements of excitation and control, placed in the housing, and connected to the transducer rod, and a mounting unit, characterized in that the housing has a streamlined shape and is made of insulating material that conducts sound vibrations and is stable aggressive liquids, while the piezoelectric element of excitation and control are mechanically connected to the housing by conducting sound vibrations of the elements and are electrically connected through an amplifier and a band-pass filter, Azuya excitation circuit of ultrasonic vibrations.  2. The sensor according to claim 1, characterized in that the housing of the sensing element has a coating with low adhesive properties.

Images