Design and Implementation of a Pressure Sensor on ...

Design and Implementation of a Pressure Sensor on Proteus: Four Sensing Intelligent Nodes Based System with a Central Monitoring Unit 1 1 Samreen Amir ,*, Ali Akbar Siddiqui1, Nimrah Ahmed , Bhawani Shankar Chowdhry2 and Ian Grout3 1

Sir Syed University of Engineering & Technology, Karachi, 2Mehran University of Engineering & Technology Jamshoro, 3University of Limerick

[email protected],[email protected],[email protected] ,[email protected],[email protected]

Abstract. This paper provides an overview of designing a Pressure sensor with its implementation on Proteus. We have worked on the concept of Autonomous Nodes with Control Unit (CU) and Master Unit (MU). When the pressure of gas increases in the pipe, the sensor senses it and the control unit will receive transmission from the active node, either to open or close the valve and actively communicates the result to master unit , whenever the status of signal changes. All the autonomous nodes are connected to MU. This system is designed to cope up with the excessive pressure of gas as to reduce the risk of accident. Keywords: PIC16F627A, Spring Based Inductive Pressure Sensor, Multisim, and Proteus.

1

Introduction

Pressure sensor is the devices that measures pressure, usually of liquids or gases and is stated as force per unit area. It can be Absolute, Vacuum Pressure Static, Gage, and Dynamic Pressure. Pressure can be measured by several derived methods like, Hydrostatic pressure, elastic deformation, behavior of gases, dynamic pressure. Pressure compresses with increase in external pressure and expands as the pressure drops. It can be categorized in terms of their pressure range, design, cost, performance, operative temperature range and the kind of pressure they determine. Piezoelectric sensors cannot sense static pressures and are used to measure fast varying pressures resulting from explosions, blasts or other cause of vibration, and are sensitive to temperature change. It can be used from about 3 psi to about 14,000 Pounds per Square Inch (psi). Absolute pressure sensor measures the pressure relative to perfect vacuum and can achieve accuracy at high temperatures. Differential pressure sensor measures the difference between two pressures, and measures flow rate or fluid levels .The potentiometric pressure sensor offers a method for obtaining an elec-

tronic output from a mechanical pressure gauge. Its pressure range is 5 and 10,000 psi. They are used in many different applications like monitoring, calibration, Level and depth sensing, weather instrumentation, aircraft, industrial process control, etc. Sensor features depends on the construction, material and dimension of structure [1]. There are several pressure sensors, their selection can be made according to our demand, but few factors should be kept in mind such as indoor and outdoor usage, vibration, electrical and mechanical interference, shock , toughness , Power consumption , accuracy, safety, temperature range, and hazardous areas like gas and oil applications. Electrical interface allows the user to attach the output of sensor to the system by means of Cables or connector’s .It can be chosen upon the environmental situation depending on the output signal. Mechanical interface describe the process link [2]. For designing Pressure sensor tools are rare, some companies are trying to develop Computer Aided Design tools for MEMS (Micro Electro Mechanical System), still they are not meeting their goal [3]. Some has designed sensor to monitor oil pressure in particular range of temperature by using FEA (Finite Element analysis) software ANSYS (Analysis System) tool [4]. The other paper focuses on the design and simulation of micro fluid sensor which can be attached to any pipe and they have been designed and simulated on MEMS tool Comsol multiphysics [5]. Micro pressure sensors are used to monitor and measure pressure in various environments by using data mining software tool machine language- WEKA (Waikato Environment for Knowledge Analysis) [6]. In this paper we have designed a sensor on Proteus which was founded in 1988. It enables our pressure sensor to tackle the pressure of Gas pipeline. Gas is transported by means of gas pipelines in a compressed state; therefore in the incident of gas leakage this can be hazardous as there is stored energy [7]. The purpose of the gas pipeline application is to check critical notification about the gas and are not only limited to transmission, gathering and distribution systems. Gas can be stored for the time being in the pipeline, through line packing which can provide gas at the time of requirement. Under some situation when the pressure and temperature increases to some extent it is possible to cause spur-of-the-moment combustion of flammable gas [8]. Monitoring gas pipelines is a significant job for safety and economical operation, loss avoidance and environmental safeguard [9]. Whenever pressure of gas increases in our pipeline, expands and contracts with the decrease of the pressure this expansion and contraction is monitored and controlled by our proposed system. Sensor node gathers information and can also communicate with each other if necessary. RF (Radio Frequency) communication is used for transmission and reception of information between sensor nodes and main CPU. In most wireless systems, a designer has two limitations: it must function over a definite distance and within a time frame transfers some amount of information. Two parameters must be considered when determining range i.e. transmitting power and receiver sensitivity. Receiver sensitivity refers to the minimum level signal the radio can demodulate. For better receiver sensitivity, lower data rates are required so it will give more range. Thus 19200 baud module has less sensitivity than 9600 baud rate and the data transferred will miss out some of the data [10]. Higher data rates require more transmission power in minimum time. Here we are working with 9600 baud rate. In our proposed

system we have designed a spring based inductive pressure sensor. This sensor will be placed inside the pipeline for measuring the pressure, when the force is applied on the spring, it contracts and it changes its area, which causes its Induction to change as well.

2

System Overview

2.1

System description

In our proposed system, we have introduced PIC16F627A for operating the relays connected to valve as well as to transmit the condition of the valve that either they are ON or OFF. PIC16F627A is a flash based 8-bit microcontroller capable of executing a single instruction in approximately 200 nanoseconds. It features an internal 4MHz oscillator, and 128 bytes of EEPROM data memory, it also has a USART (Universal Synchronous Asynchronous Receive Transmitter) that is used to communicate with other devices serially either by wired or wireless communication [11]. The purpose of PIC16F627A microcontroller is to monitor the pressure in the Gas line and adjust the valve according to the condition required, the calibration is done in accordance that if the pressure in the line rises up to 20 psi (Pounds per square inch) our PIC16F627A microcontroller will turn OFF the valve and then update this knowledge to the main CPU. This main CPU will display the status of the values, which are wirelessly interfaced with the nodes via RF Transceivers. In our proposed system we have designed four identical nodes, and each node is wirelessly apart from each other are interfaced with the main CPU. We have designed a spring based inductive intelligent pressure sensor capable of measuring the pressure in psi; eq (1) demonstrates the formula for the conversion in psi. When force is applied on the pressure sensor it contracts.

(1) When this contraction occurs, the area of that spring changes, and change in the area of the spring will directly affect the inductance of the Inductor. When a force in applied on the spring the area of that spring will change accordingly. When this contraction occurs, the area of that spring changes, and change in the area of the spring will directly affect the inductance of the Inductor. When a force in applied on the spring the area of that spring will change accordingly. (2) Where, L is Inductance, N is the number of turn of winding, µ is the relative permittivity, A is the Area, ᵖis the length. (3)

Where,

is the Impedance,

is the Reactance.

Often it is required to measure the pressure in unsteady environmental conditions, the measurement of the time varying pressure sensor it of utmost importance and in response to such kind of cases, phenomena like the time or frequency response of pressure measuring systems consists of Valves etc. are required and it is important not to neglect various other parameters. Mathematical model of the Inductive sensor resembles to that of a simple RL circuit, with the Inductive change that occurs when the area contracts, (4) The equation (4) is the first order Time Domain representation, and by applying Laplace Transform we can convert it into frequency domain which is represented by equation (5). (5)

Fig. 1. Step Response of uncompensated sensor at 20 psi

In our system area and length are the two factors affecting our Inductive Transducer. Fig.1 shows the step response of an uncompensated result of the inductive sensor’s transfer function. Due to this change in the induction there will be a certain change in the Inductor Voltage (VL); this is basically the Voltage that has to be fed to the PIC16F627A microcontroller for the purpose of controlling the valve, and to update the status of the value to the main CPU via RF Transceiver. Table.1. Shows the changes occurs due to the certain change in Inductance (L) when affected by the force.

Table 1. Showing the changes occurring in different parameters. Area 2

2 mm 2 4 mm 2 6 mm 2 8 mm 2 10 mm 2 12 mm 2 14 mm 2 16 mm 2 18 mm 2 20 mm

Change in Inductance (L) 10uH 9uH 8uH 7uH 6uH 5uH 4uH 3uH 2uH 1uH

3.77mV 3.39mV 3.02mV 2.64mV 2.26mV 1.88mV 1.51mV 1.13mV 0.753mV 0.377mV

Pressure in (psi) 20 19 18 17 16 15 14 13 12 11

Table.1 represents the changes occurring up till the value where the valve will turn off. It also clearly shows the approximate change in the value of VL. This means the change in 1uH Inductance will change the VL by 0.38mV approximately.

Fig. 2. Block Diagram of the Whole Hardware System.

Fig.2 demonstrates a complete block diagram of our proposed system, which shows all four nodes with transceivers, interfaced wirelessly with main CPU. Each valve is

also interfaced with our PIC16F627A microcontroller which is controlled by the Relay separately.

2.2

Software Description

In our proposed system, we have used MicroC pro for programming or PIC16F627A. Micro C pro consists of all the libraries and tools to design our desired software. The simulated design of our complete hardware is built on Proteus. The ISIS Schematic Capture of Proteus is used for the designing purpose. Multisim is used to design an inductive Transducer. Matlab is also used to simulate the result of the designed sensor to observe the parameters more closely. Fig.3. is the flow chart of complete software Model in stepwise manner. After system initialization each PIC16F627A microcontroller of separate nodes continuously monitor the Sensors interfaced to each of them, and will only turn the value OFF only if the Pressure reaches to 20 PSI, and simultaneously will also update the main CPU via RF Transceiver about the status of the Valve that either it is in On condition or OFF.

Fig. 3. Block Diagram of the Software System

3

Results

The results of our proposed system are tested on the Proteus environment clearly showing the working system model. Fig.4 demonstrates the status of the valves that

were updated by the PIC16F627A microcontroller wirelessly, whether the valves are in On or OFF condition.

Fig. 4. Complete Simulated System Model on Proteus

Fig. 5. Complete System with Valve Status.

Fig.5. Result represents an individual Node with serial communication, which is use for interfacing the RF Transceiver that communicates the main CPU with each of our Nodes.

Fig. 6. Single Node of a complete System

Fig.6. represents an individual Node with serial communication, which is use for interfacing the RF Transceiver that communicates the main CPU with each of our Nodes. The Inductive Transducer is tested using variable Inductor, and implemented on the Multisim environment, thus the following results were accumulated.

Fig. 7. Represent the output at 10uH

Fig.7 result demonstrates an output at 10uH, at this point the Area of the spring is of 2 mm2. This means that the spring is contract at the point representing the reading has reached to its maximum value that is 20 PSI; we can clearly see the voltage output is 3.77mV as shown in Table (1). This is the voltage that is fed to our PIC16F627A microcontroller for processing after converting it in Digital format using ADC.

Fig. 8. Represent the output at 9uH.

Fig.8 result demonstrates an output at 9uH, at this point the Area of the spring is of 4mm2. This represent that the spring has contracted and the Pressure has reached to the 18 PSI. Which represented the voltage output is 3.39mV as demonstrated in the Table (1).

Fig. 9. Represent the output at 1uH.

Fig.9 result demonstrates an output at 1uH, at this point the Area of the spring is of 20mm2 .This represents that’s the spring has not contracted enough and the pressure is at low level that is 11 psi, and there is no danger to a Gas Line. Which represented the voltage output is 0.377mV as demonstrated in the Table (1). These results are taken in accordance to the system operation.

Fig. 10. Represent the graphical output of parameters such as psi with respect to Area, and L with respect to VL.

Fig. 11. Represent the graphical output of the parameters, that shows the how changes occurs in different parameters involve in the sensor system such as psi with respect to area, and Voltage with respect to inductance.

4

Conclusion

In our proposed system, we have introduced an idea of cheaper way to measure pressure in environment such as Pipelines. The entire system is simulated, and compiled in Proteus environment. The design of the pressure sensor using variable inductor is implemented in Multisim environment. Apart from our work, many different software tools are used to construct these sensors, which are either costly or unavailable for the commercially or for a small industry. Our proposed system performed according to our desired parameter, and can easily be implemented in Industry for the monitoring purpose of gas, and fluids etc.

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