SU750293A1 - Apparatus for measuring temperature - Google Patents

Description

The invention relates to devices for measuring temperature and can be used in various fields of technology, in particular, in systems of operational and automatic monitoring and control of productive technological processes in the chemical, food and other industries. A device for temperature measurement is known, comprising a temperature-sensitive element filled with a working (thermometric) fluid, a separating elastic element (bellows or membrane) and a device for converting thermal expansion of the liquid into an output signal of the device 1. The closest in technical essence to the present invention is a device for measuring temperature, comprising a temperature-sensitive element, comprising a separating bellows placed in a housing filled with a working fluid, with a float placed in it, and a force-to-output conversion mechanism 23. A disadvantage of the known device is that the accuracy of temperature measurement and large inertia are not high enough, due to the presence of friction units and a significant amount of working fluid in the temperature-sensitive element. The accuracy of the device is directly proportional to the amount of working fluid in the temperature-sensitive element, and an increase in the amount of working fluid leads to an increase in temperature inertia, i.e. to reduce accuracy. The aim of the invention is to improve the measurement accuracy and reduce the inertia of the device. The goal is achieved by the fact that in the device for temperature measurement the float is made of two cavities, a sealed partition between which is connected to a movable rim of the separating bellows and has a channel that informs the working cavity of the temperature-sensitive element with the upper cavity of the float, the lower part communicated with the atmosphere, with the outer end

The upper cavity of the float is connected to the force-to-output conversion mechanism, while the lower part of the float is placed in the working fluid 1C with a gap of about 0.51.00 mm relative to the inner surface of the housing of the temperature-sensitive element. The schematic diagram of the device is shown.

The fixed side of the separating bellows 2 is welded to the case of the thermosensitive element 1. In the case, there is a float 3, divided by a partition 4 into two cavities, the lower 5 and the upper b. The partition 4 is welded to the movable side of the bellows 2. The working cavity of the temperature-sensitive element (the cavity between the housing 1, the bellows 2 and the float 3) is filled with working (thermometric) fluid 7. Moreover, the working fluid completely surrounds the lower part 5 of the float 3 and through the channel 8 of a small section, drilled in the partition 4, communicates with the cavity of the upper part b of the float 3, partially filled with the same liquid. The upper part of the float 6 (the space above the working fluid) through the capillary coil 9 is in communication with the atmosphere. The upper outer end of the float 3 by the rod 10 is connected with the lever system of the pneumo-force transducer 11, the node of the nozzle-valve 12 of which processes the output signal of the device. The housing 1 of the temperature-sensitive element of the device is mounted on the process tank 13, the temperature of the medium in which is controlled. The dimensions of the float 3 are made so that the gap between the outer surfaces of the lower part 5 of the float and the inner surfaces of the lower part 5 of the float and the inner surfaces of the housing 1 and the bellows 2 is kept to a minimum sufficient to separate these surfaces - about 0.5- 1.0 mm. Thus, the amount of work. fluid 7 is minimal.

The amount of working fluid filling part of the volume of the upper cavity b of the float 3 and the volume of this cavity are calculated depending on the coefficient of volumetric expansion of the working liquid and the measurement limit of the device. Criteria for such a calculation are the requirements that at the minimum temperature measured by the device the level of working fluid 7 in the upper cavity 6 of the float 3 should not be lower than the partition wall 4, and at the maximum temperature should not exceed the base of the capillary 9.

The unit works in the following manner.

In the initial position, at a steady-state temperature of the controlled medium in the tank 13, the kinematic system of the device is in equilibrium, due to the equality of the immersing and pushing forces acting on the lower part of the float 5 immersed in the working fluid 7,

: i)

Pb

about,

+

P

where FP is the working force of the temperature-sensitive element;

RP immersing force acting on the float is equal to the weight of the float;

F, the buoyant force acting on the float, depending on the volume of the part of the float immersed in the working fluid and on the density of the working fluid.

When the temperature of the controlled medium changes, the equilibrium / expressed by equation (1) is violated. For example, as the temperature rises, the density of the working fluid decreases, and the buoyant force acting on the float decreases by

 Rzh / t-s

(2)

where D F.J. - change of pushing force;

VP is the external volume of the float part immersed in the working fluid (the lower part 5 of the float 3); : pjj, - initial working density

liquid;

| 3 - coefficient of temperature volumetric expansion of the working fluid;

At is the change in temperature of the controlled medium (and the working fluid);

g is the acceleration of the force of gravity. At the same time (with the same change in the temperature of the working fluid At) the volume of the working fluid 7 in the temperature-sensitive element will increase. This increase in the volume of the working fluid is determined by the expression

 (3)

where - the change in the volume of work

liquids; Vjj - the initial volume of the working

fluid.

This additional volume AV, of the working fluid through channel 8 flows from the working chamber of the temperature-sensitive element into the upper cavity b of the float 3, raising the level of the working fluid in this cavity. This increase in the level of liquid in the upper cavity b of the float 3 leads to an increase in the weight of the float by

(C)

l p f-Rzh65 Where dsp - change in weight poplabka.

Claims (2)

Claim 1. A device for measuring temperature, comprising a heat-sensitive element, including a separation bellows with a float placed in a housing filled with a working fluid, and a mechanism for converting the force into an output signal, characterized in that, in order to increase the accuracy of measurement and reduce inertia device, the float in it is made of two cavities, a sealed partition between which is connected to the movable side of the separation bellows and has a channel that communicates the working cavity of the thermal sensing an element with an upper cavity of the float, the lower part of which is filled with a working fluid, and the upper is in communication with the atmosphere, the outer end of the upper cavity of the float with a mechanism for converting the force into an output signal. 2. · The device according to claim 1, characterized in that the lower part of the float is placed in the working fluid with a gap of the order of 0.51.0 mm relative to the inner surface of the body of the heat-sensitive element.