Membrane Pressure Transmitter Design

Contents

Introduction

1. Sensor Purpose, Operation and Design

2. Analysis of errors occurring in the instrument

3. Technical sketch justification

4. Calculation of static and dynamic parameters of the sensor

4.1. Calculation of sensitive element (corrugated membrane)

4.2. Calculation of sensitivity of converter elements

4.3. Motion Sensor Calculation

4.4. Determination of membrane natural oscillation frequency

4.5. Calculation of the instrument sensitivity threshold

Literature

Introduction.

The rapid development of modern aircraft instrumentation and the creation of new types of aircraft lead to tougher requirements for flight control automation. Sensors with electrical output signals, which are necessary for control of operation modes of all aircraft units and aerobatic navigation flight mode, such as accelerometers, altimeters, angular velocity sensors, pressure gauges, tracking systems, fuel meters, integrating gyroscopes, gyroscopic integrators of linear accelerations, etc. play a huge role in this.

The operating conditions of aircraft instruments differ significantly from the operating conditions of ground-based measuring devices, therefore, when designing them, these conditions must first be taken into account. Aircraft devices operate in a wide range of changes in ambient temperature, under the influence of moisture, dust, vibrations, accelerations, etc. Thus, the main indicators of the efficiency and quality of aircraft devices are high accuracy and reliability when operating in difficult operating conditions, small dimensions and weight, as well as low cost.

Pressure sensors (pressure gauges, vacuum meters, barometers) are widespread in aircraft instrumentation. They are designed to measure the fuel pressure supplied to the engine, oil, air pressure, pressure drop in the engine gas paths, as well as variable pressures in the engine combustion chambers.

The purpose of the course work is to develop a pressure sensor. This work develops a schematic diagram of the sensor, performs a technical sketch of its design, calculates the main static and dynamic parameters of the device and performs working drawings of individual units and elements.

The explanatory note presents the following sections:

1. Purpose, operation and design of the sensor. This section describes the purpose and operation of the device, analyses and justifies its schematic diagram.

2. Analysis of errors occurring in the instrument. This section analyzes the main sources of errors and describes how they can be reduced.

3. Justification of technical sketch. This section describes the design and operation of the device and its elements, analyzes the advantages and disadvantages of the used elements and provides justification for the selection, selection and justification of structural materials.

4. Calculation of static and dynamic parameters of the sensor. This section describes methods and results of calculation of converter elements, static and dynamic parameters of the designed instrument.

3. Justification of technical sketch.

The development of the technical sketch is carried out on the basis of the analysis of the technical literature and the selected analogue, that is, the instrument from among those developed and mastered by the industry, which is closest in composition of the elements, structural diagram and dimensions to the given pressure sensor.

The dimensions of the instrument under development are 30 * 30 * 40 mm. Sensor elements are arranged in cylindrical housing made of aluminium Al2 (GOST 158393). This alloy has high casting properties, satisfactory corrosion resistance, can work for a long time at sufficiently high temperatures. It is designed to make thin-walled parts of complex configuration.

The sensitive element is a corrugated membrane with high sensitivity and linearity of static characteristic. The membrane is made of beryllium bronze BrBNT1.7 (GOST 1817578). This material has high strength and wear resistance, very good elastic properties.

The transfer-multiplier mechanism is a device that provides the necessary angular movement of the brush along the winding of the potentiometer with a small movement of the rigid center of the membrane. For the developed device, a tangent cam gear is chosen, since it is easy to manufacture and has a constant gear ratio during small movements of the pusher.

The axis of the movable system is made of structural steel 40KHN2MA (GOST 454371), which has high strength, ductility and viscosity. This is facilitated by a high nickel content. The disadvantage of this steel is the difficulty of cutting them. Journals pressed into axle are installed in cylindrical supports. The bushing and bearing are made of corundum, which, like other technical stones, has high strength, hardness, wear resistance, has a very small coefficient of friction. Bushing and bearing are filled into housing strut.

The displacement sensor is a potentiometer connected according to a rheostatic scheme. The characteristic of potentiometers is quite accurate and stable and depends little on the influence of external conditions (temperature, humidity). Potentiometers have a relatively high output voltage, which does not require subsequent amplification in many cases. However, the potentiometer has one significant drawback: its sliding contact causes abrasion and wear of the brush and wire. Therefore, potentiometers are in some cases replaced by more reliable non-contact electrical elements, and yet the simplicity of the design and small dimensions of potentiometers remain attractive to designers.

The carcass material shall have sufficient mechanical strength and rigidity, moisture resistance and heat resistance so as not to deform when the temperature and humidity of the air change. The frame must also remove heat from the potentiometer winding, which allows a larger current to pass through it. The potentiometer frame is made of AMg2 alloy (GOST 478497), which has all the listed properties. In addition, AMg2 is well polished, which is necessary for the manufacture of potentiometers. The winding wire material shall have high electrical resistivity, low thermal coefficient of electrical resistance, strength, corrosion resistance and wear resistance. In this device, the winding is made of an alloy PdCp40 that satisfies all these conditions. The disadvantage of this material is the high cost. The wire is wound tightly onto the frame, turn to turn, after which the surface is covered with a thin uniform layer of varnish to protect the turns from displacement. Insulation layer covered with wire is partially cleaned in one place to form contact track along which brush moves.

The brush is made of two wires of platinum-iridium alloy fixed on the brush holder. The length of the brush should be such that no resonance phenomenon is observed during vibration.

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