CN104568054B - A kind of heated type difference thermal resistance liquid level sensor and its method for measuring liquid level - Google Patents

Abstract

The invention belongs to the field of sensor technology and thermal parameter measurement, in particular to a heating type differential thermal resistance liquid level sensor and a method for measuring liquid level. In this method, the same part of two armored thermal resistors of the same structure and quality as the sensitive element is placed at the position of the liquid surface to be measured, and the heating wire of one of the sensitive elements is heated by electricity, which is used as the measuring element, and the other The heating wire of the sensitive element is not energized, and it is used as a compensation element; as the liquid level changes, the resistance difference of the thermal resistance wire in the two sensitive elements is measured through the resistance measurement circuit, and the liquid level height and resistance obtained according to the test The relationship between the differences is calculated to obtain the liquid level height. The liquid level sensor provided by the invention has the advantages of simple structure, reliable performance, high sensitivity and strong anti-interference ability.

Description

A heating type differential thermal resistance liquid level sensor and its method for measuring liquid level

technical field

The invention belongs to the field of sensor technology and thermal parameter measurement, and in particular relates to a heating type differential thermal resistance liquid level sensor and a method for measuring the liquid level.

Background technique

At present, the liquid level measurement of many liquid storage tanks/containers or liquid storage tanks in the industry mostly uses differential pressure liquid level gauges, float level gauges, magnetic liquid level gauges, ultrasonic liquid level gauges, radar liquid level gauges, etc. Some of these liquid level gauges need to open holes on the liquid storage tank/container or liquid storage pool, which brings a risk of leakage; some are affected by medium density fluctuations; some are not reliable; some have a short service life; some are not suitable for high temperature , high pressure, high radioactivity and other harsh environments. Therefore, there is an urgent need for a liquid level measuring instrument that does not need to open holes in the liquid storage tank/container or liquid storage pool, has high reliability, long service life, and is suitable for use in harsh environments.

Contents of the invention

The object of the present invention is to provide a heating type differential thermal resistance liquid level sensor with simple structure, reliable performance, high sensitivity and strong anti-interference ability and a method for measuring liquid level.

The technical scheme of the present invention is as follows: a heating type differential thermal resistance liquid level sensor, including two armored thermal resistors with the same structure and equal quality as sensitive elements, and the armored casing of the armored thermal resistors is provided with a thermal resistor Wire and heating wire, insulating material is provided between the thermal resistance wire, heating wire, and armored sleeve, and the thermal resistance wires of the two sensitive elements are connected with the resistance measuring circuit; the heating wire of one of the sensitive elements is energized Heating, the heating wire of the other sensitive element is not energized.

Further, in the above-mentioned heating differential thermal resistance liquid level sensor, wherein, the two armored thermal resistances are insulated and connected through a thermal insulation bracket, and are separated by a certain distance.

Further, the above-mentioned heating type differential thermal resistance liquid level sensor, wherein the thermal resistance wire is nickel wire; the armored sleeve is made of 316L stainless steel; the insulating material is MgO; The heating wire is made of Ni80Cr20 material.

A method for measuring liquid level using the above-mentioned heating type differential thermal resistance liquid level sensor. In this method, the same parts of two armored thermal resistances with the same structure and equal mass as sensitive elements are placed at the position of the liquid surface to be measured, and one of them is The heating wire of the sensitive element is heated by electricity, which is used as the measuring element, and the heating wire of the other sensitive element is not energized, which is used as the compensation element; as the liquid level changes, the two sensitive elements are measured by the resistance measuring circuit The resistance difference of the medium thermal resistance wire is calculated according to the relationship between the liquid level height and the resistance difference obtained by the test to obtain the liquid level height.

Further, the above-mentioned method for measuring liquid level with a heating type differential thermal resistance liquid level sensor, wherein the relationship between the liquid level height and the resistance difference is H=A+BΔR or H=A+BΔR+CΔR ² ,

H is the liquid level height, ΔR is the resistance difference, A, B, C are the constants determined by the experiment.

Further, the above-mentioned method for measuring liquid level with a heating type differential thermal resistance liquid level sensor, wherein the resistance difference is obtained by differentially connecting the thermal resistance wires in the two sensitive elements, or measuring the two independently. It is obtained by subtracting the resistance value of the thermal resistance wire in the sensitive element.

The beneficial effects of the present invention are as follows: the present invention utilizes the obvious difference in heat transfer performance between gas (steam) body and liquid (such as water), and the temperature difference between the sections of the two sensitive elements in the liquid is very small, that is, the two sensitive elements The resistance difference between the sensitive elements is very small, and the temperature difference in this section in the gas (steam) body is large, that is, the resistance difference is also large. As the liquid level increases, the total resistance difference between the two sensitive elements becomes smaller, that is, the higher the liquid level, the smaller the total resistance difference between the two sensitive elements. With the help of this law, the relationship between the liquid level H and the thermal resistance value difference ΔR is derived, so that the liquid level can be continuously measured by ΔR. The invention has the advantages of simple structure, reliable performance, high sensitivity and strong anti-interference ability.

Description of drawings

Fig. 1 is a structural schematic diagram of a heating type differential thermal resistance liquid level sensor.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

The liquid level sensor provided by the present invention uses two armored thermal resistors of the same structure and equal quality as sensitive elements, and the thermal resistance wire in one of the sensitive elements is heated by heating wire to sense the liquid level, which is called a measuring element. . The other is not heated by electricity, and it is used to measure the ambient temperature and compensate for the influence of the ambient temperature, which is called a compensation element. The thermal resistances of the two sensitive elements are connected differentially or output independently, and the resistance values are subtracted to form a resistance difference. The specific resistance measurement method is a well-known technology in the art, and will not be repeated here. The liquid level sensor utilizes the obvious difference in heat transfer performance between gas (steam) body and liquid (such as water), and the temperature difference between the section of the two sensitive elements in the liquid is very small, that is, the temperature difference between the two sensitive elements The difference in resistance is very small, and the temperature difference in this section of the gas (steam) body is large, that is, the difference in resistance is also large. As the liquid level increases, the total resistance difference between the two sensitive elements becomes smaller, that is, the higher the liquid level, the smaller the total resistance difference between the two sensitive elements. With the help of this law, the relationship between the liquid level height H and the thermal resistance difference ΔR is derived through experiments H=A+BΔR or H=A+BΔR+CΔR ² , where the constants A, B and C are usually determined by experiments To determine, which relational formula to use can be determined according to the linear relationship between the liquid level height and the resistance difference obtained by the experiment. Thus, the liquid level can be continuously measured by ΔR.

As shown in Figure 1, a heating type differential thermal resistance liquid level sensor provided by the present invention is composed of two armored thermal resistances 1 and 2 of the same structure and equal quality as sensitive elements, and the armored thermal resistances of the armored thermal resistances The casing 6 is provided with a thermal resistance wire 3 and a heating wire 5, an insulating material 4 is provided between the thermal resistance wire 3, the heating wire 5 and the armored casing 6, and the two armored thermal resistances 1 and 2 They are insulated and connected to each other through the heat insulating bracket 7, and are separated by a certain distance to ensure that they will not affect each other, and the two thermal resistance wires are connected to the resistance measuring circuit. Place the same part of two armored thermal resistors with the same structure and quality as the sensitive element at the position of the liquid surface to be measured, and the thermal resistance wire in one of the sensitive elements is heated by the heating wire to make it higher than the surrounding gas ( A certain temperature of the vapor) body medium, generally about 30-50°C, is used to sense the liquid level; the other is not heated by electricity, and is used to measure the ambient temperature. The thermal resistance of the two sensitive elements is differentially connected or output independently to obtain the resistance difference, and the relationship between the liquid level height and the resistance difference is obtained through experiments, so as to continuously measure the liquid level.

A specific example of the present invention is that the outer diameter of the armored casing 6 is 4.5mm, the inner diameter is 4.0mm, and the material is 316L stainless steel; the thermal resistance wire 3 adopts nickel wire with a purity of 99.2%; the insulating material 4 adopts MgO, the purity 99.4%; the material of the heating wire 5 is Ni80Cr20. The total length of the sensor is 2000mm. In H=A+BΔR, A=2.68X10 ³ , B=-45.69. In addition, the thermal resistance wire 3 can also be replaced by raw materials such as platinum or copper.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies, the present invention also intends to include these modifications and variations.

Claims (2)

1. a kind of method of heated type difference thermal resistance liquid level sensor measurement liquid level, it is characterised in that：The heated type difference Thermal resistance liquid level sensor includes two armoured thermal resistances (1,2) with quality such as structures as sensing element, the armouring Hot water radiation wire (3) and heater strip (5) are equipped in the armor sleeve (6) of thermal resistance, the hot water radiation wire (3), heater strip (5), Insulating materials (4) are equipped between armor sleeve (6), the hot water radiation wire of two sensing elements is connect with resistance value measuring circuit；The party Method will be placed in tested liquid level position as the two of sensing element same sections with the armoured thermal resistance of the quality such as structure, wherein The heater strip electrified regulation of one sensing element, uses it to as measuring cell, the heater strip no power of another sensing element, It uses it to as compensating element,；With the variation of liquid level, hot water radiation wire in two sensing elements is measured by resistance value measuring circuit Resistance difference, according to test obtained liquid level and resistance difference between relationship liquid level is calculated, it is described Relationship between liquid level and resistance difference is

H=A+B Δ R or H=A+B Δ R+C Δ R²,

H is liquid level, and Δ R is resistance difference, and A, B, C are the determining constant of test.

2. the method for heated type difference thermal resistance liquid level sensor measurement liquid level as described in claim 1, it is characterised in that：Institute The resistance difference stated is obtained by will measure after hot water radiation wire progress difference connection in two sensing elements, alternatively, independent measurement Subtract each other to obtain after hot water radiation wire resistance value in two sensing elements.