The transmitter used in industrial automation control transmits and detects the working variables of the liquid, such as pressure, liquid level, temperature, flow, specific gravity, etc., for monitoring and controlling the operation of the process.
Diaphragm pressure transmitter is an automatic instrument for measuring fluid pressure in the industrial field. It is mainly composed of a pressure measuring probe, a capillary tube, a filling liquid and a pressure transmitter. One end of the pressure measuring probe is provided with an elastic metal diaphragm. A closed cavity is formed between the diaphragm and the pressure measuring probe; the pressure measuring probe has a filling port for filling the closed cavity with filling liquid; one end of the capillary is connected to the closed cavity, and the other end of the capillary is connected to the pressure transmitter Head; Filling liquid (such as silicone oil, fluorine oil, etc.) is filled into the closed cavity through the filling port. When the closed cavity and capillary are filled, the filling port can be blocked. When in use, the measured medium is brought into contact with the elastic metal diaphragm, and the fluid acts on the elastic metal diaphragm to deform the elastic metal diaphragm under pressure. According to Pascal’s law, part of the pressure of the fluid in the closed container changes and the size remains unchanged The ground is transmitted in all directions, and the capillary tube and the airtight cavity on the pressure measuring probe communicate with each other and are in a closed state. Therefore, when the elastic metal diaphragm is deformed, the fluid pressure acting on the elastic metal diaphragm will be filled through the capillary The liquid is transferred to the pressure transmitter, and the pressure transmitter converts the detected pressure into a standard electrical signal and displays it, thus realizing the measurement of fluid pressure.
Existing diaphragm pressure transmitters have the following shortcomings: when the temperature of the measured medium is too high or the temperature rises and falls sharply, the filling liquid will undergo a large change in volume due to the nature of thermal expansion and contraction, and the volume of the filling liquid The change will cause internal pressure, which will act on the pressure-sensitive diaphragm of the pressure transmitter, which will distort the pressure signal received by the pressure transmitter, which will affect the measurement accuracy and increase the measurement error.
For the existing diaphragm pressure transmitter, when the temperature of the measured medium is too high or the temperature rises and falls sharply, the filling fluid will undergo a large change in volume due to thermal expansion and contraction, which will cause the pressure transmitter to receive The pressure signal is distorted, which affects the measurement accuracy and increases the defect of measurement error. The present invention provides a diaphragm pressure transmitter.
The invention includes a pressure measuring unit, a pressure conducting unit and a pressure transmitting unit which are sequentially connected; a sealed cavity is formed between the pressure measuring unit and the pressure conducting unit; and the sealed cavity is provided with a liquid metal filling liquid for conducting pressure. A heating device is arranged outside the pressure measuring unit and the pressure conducting unit; the heating device is used for heating the liquid metal filling liquid in the sealed cavity.
The heating power of the heating device is 1-300W. The side of the sealed cavity is provided with a liquid metal filling port for filling the sealed cavity with liquid metal filling liquid. The pressure measurement unit includes a pressure measurement probe; the pressure transmission unit includes a capillary tube; one end of the pressure measurement probe is provided with a pressure sensing module for detecting the pressure of the measured medium, and the other end of the pressure measurement probe is connected to the pressure transmission unit through the capillary tube; the pressure sensing module A sealed cavity is formed between the capillary and the capillary tube. The inner diameter of the capillary is 2-30mm. The pressure transmitting unit includes a pressure transmitting head; the pressure transmitter is used to convert the pressure difference signal transmitted by the pressure sensing module through the liquid metal filling liquid into an electric signal and display it.
The pressure sensing module includes an elastic metal diaphragm. The shape of the elastic metal diaphragm is circular; the area of the metal diaphragm is 0.5-100 cm2. Liquid metal filling fluids include, but are not limited to, any of the following and combinations thereof: bismuth-based, indium-based and tin-based alloys with a melting point lower than 230°C.
The diaphragm pressure transmitter of the present invention includes a pressure measurement unit, a pressure transmission unit, and a pressure transmission unit, and a sealed cavity is formed between the pressure measurement unit and the pressure transmission unit, and a liquid metal filling liquid for transmitting pressure is arranged therein. Since the thermal expansion coefficient of liquid metal is much smaller than the non-metallic filling fluid (such as silicone oil, fluorine oil, etc.) commonly used in existing transmitters, the measurement accuracy can be improved when measuring fluid media with high temperatures or drastic changes in temperature. Liquid metal has a high boiling point, that is, it has a very wide liquid temperature range, so it can measure the pressure of a higher temperature fluid; and most low melting point metals (except mercury) have very low volatility, so they are used as filling fluids for high temperature fluids When pressure is measured, its own loss is very small.