Oxygen Level Monitoring in an Oxygen Cyl

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IEEE-Intenational Conference On Advances In Engineering, Science And Management (lCAESM -2012) March 30,31,2012 592

Oxygen Level Monitoring in an Oxygen Cylinder

Santhosh K v, B K Roy, Member, IEEE, Pankaj Kumar Bhowmik Department of Electrical Engineering

National Institute of Tecnology, Silchar, India

_

Abstract- This paper aims at designing an oxygen level monitoring technique in an oxygen cylinder. The amount of oxygen present inside the oxygen cylinder is very vital information when such cylinder is in use for supply of oxygen to a critical patient. The amount of oxygen present inside the cylinder is measured by the pressure at the outlet nozzle. The pressure is measured using a high precision MEMS Pressure Sensor. The output of the MEMS pressure sensor is voltage of the order milli. An ampliier is used to amplify this milli volt signal.

A microcontroller is used in cascade to process the signal and display the pressure of oxygen cylinder. Also a buzzer is given which cautions the attendants of patient whenever the level of oxygen is below a pre-decided value. The signal is further transmitted to the monitoring station through wireless communication module. Graphical display is used at monitoring station to indicate the pressure in the oxygen cylinders to initiate actions like replacement of empty cylinders with illed ones.

Experimental results show that. The aims set for this paper are achieved satisfactorily.

Indx Terms- Oygen Cyinder, MEMS Pressure Sensor, Lab VIEW,

I. INTRODUCTION

O

xygen is our primary life-support. The air we breathe is so vital that without it we would rapidly die. Clean air is made up of several gases of which Oxygen is the most important to us. Clean air contains 19%-21 % Oxygen. The generation and maintenance of all our body processes are supported by four basic life-support components:

carbohydrates, water, proteins and energy. Most Scientists agree that oxygen is actually the over-riding key ingredient in all four life-support components. The oxygen concentration in a healthy human body is approximately three times than that of air. When body oxygen falls to extremely low levels for prolonged periods of time, the body may become a breeding ground for harmul bacteria, viruses, ungi, parasites and other infectious agents. Most of these are anaerobic, i.e. they cannot live in an oxygen-rich environment. Some research indicates that when the oxygen content of the body is within the nomal level, infectious microorganisms have a more dificult time for

breeding and multiplying. The partial pressure of oxygen in normal blood should be approximately 97%. Within each red blood cell there are iron-rich hemoglobin molecules.

Approximately 97% of the oxygen carried to the cells is attached to these hemoglobin molecules and 3% of the oxygen supply dissolved in the blood plasma. When the blood oxygen levels remain low for extended periods of time, the cells cannot get an adequate and consistent supply of oxygen and there may be dificulty in resisting the invasion of microorganisms resulting in lessening of natural life-support

[1]- [4].

Under this circumstance when lungs of a human body fail to take appropriate amount of oxygen inside the body, an oxygen cylinder is used to pump oxygen to the human body. Thus appropriate arrangement for supply of oxygen rom an oxygen cylinder can be termed as one of the live saving device. It is very important to continuously monitor the status of such devices. Seldom it is seen that the amount of oxygen contains inside the cylinder is unnoticed. When the patient's feels uncomfortable due to non availability of oxygen in cylinder, suddenly there are rushes and may lead to severe consequences.

So this paper proposes a technique which will keep track of the oxygen levels centrally in the cylinders present in a hospital. It also does the local measurement of oxygen level in the cylinder and a buzzer beeps when the oxygen level in the oxygen cylinder is dropped below a pre-decided value so that attendant of a patient can be alert along with on duty nurses and ward boys for additional backup. For this purpose a MEMS pressure sensor is used to measure the pressure followed by an ampliier to ampliy the output of MEMS pressure sensor. The output of ampliier is sent to a micro

controller to process the signal and display the actual pressure and a buzzer beeps when the pressure drops below a predeined lower level. Further, oxygen level is also transmitted to the monitoring station using wireless communication to keep track of the status of the cylinders.

Since the oxygen cylinder is portable, the power needed for the proposed device is derived rom a battery. It is important to monitor the condition of battery; this is also taken care in the proposed technique. At the monitoring station LabVIEW

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IEEE-Intenational Conference On Advances In Engineering, Science And Management (lCAESM -2012) March 30,31,2012 593 sotware is used to accept the data and graphically displays the

levels on the ront panel.

The paper is organised as follows: ater introduction in Section-I, Section-II deals with the experimental setup, a brief description on MEMS pressure sensor is given in Section-III.

The output of the sensor is ampliied and transmitted; a brief discussion on data conversion unit is discussed in Section-IV.

Section-V deals with the problem statement followed by proposed solution in Section-VI. Finally, result and conclusion is given in Section-VII.

II. EXPERIMENTAL SETUP

The proposed measurement technique is carried out with the help of an experimental set up as shown in Fig 1. Here a pressure nozzle is used to sense the pressure head of the oxygen cylinder. MEMS pressure sensor is used at the end of the nozzle to sense the oxygen pressure. Once the pressure is sensed by the MEMS pressure sensor, it is passed to the data conversion unit and micro-controller to process the data. The output is displayed using a LCD display and activates the buzzer when required. The F transmitter module is designed to transmit the oxygen level data to the monitoring station. An additional circuit is added to indicate battery level. A red LED will glow if the battery level is low else a green LED will glow. The Fig. l shows the circuit board for realizing the above mentioned unctions. The circuit board is shown in Fig.

1 can be placed on the oxygen cylinder and the F receiver is placed at the monitoring station to acquire signals and initiate

Fig I. Experimental setup of the proposed technique

The block diagram representation of the proposed technique is given in Fig 2 and Fig 3. Fig 2 shows the block diagram of circuit board with transmitter module placed on the oxygen cylinder, Fig 3 shows the block diagram receiver

MEMS Pr�\sllr�

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Fig 2. Block diagram of the circuit board with transmiter block placed on the oxygen cylinder

>C with LabVIW Fig 3. Block diagram of the receiver block at monitoring station

III. MEMS SENSOR

The SX series of pressure sensors provides the most cost effective method of measuring pressures. These sensors are speciically designed to be used with non-corrosive and non

ionic media, such as air and dry gases. Convenient pressure ranges are available to measure differential pressure. The absolute devices have an intenal vacuum reference and the output voltage is proportional to absolute pressure. The differential devices allow application of pressure to either side of the diaphragm and can be used for gage or differential pressure measurements. This product is packaged either in SenSym's standard low cost chip carrier "button" package, a plastic ported "N" package or a dual inline package (DIP). All packages are designed for applications where the sensing element is to be integral to the OEM equipment. Because of its high-impedance bridge, the SX series is ideal for portable and low power or battery operated systems. Due to its low noise, the SX is an excellent choice for medical and low pressure measurements. Here SX 150 which is an absolute device is used. Fig 4 shows the picture of the sensor used for the proposed system. [5],[6].

Fig 4. SX 150 sensor

IV. DATA CONVERSION UNIT

module connected to the PC placed in monitoring station. _3.1_Amplier

Since the voltage output of the MEMS sensor is in the order of a few milli volts, it requires an ampliier to bring it in the order of volts. For the purpose a non inverting ampliier designed using LM 324, operational ampliier is used. The gain of the ampliier can be controlled by varying the ratios of R, and R2 as shown in Fig 5

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Rz

Fig 5. Ampliier using LM 324

3.2 Wireless communication (F module)

For acquiring the information on oxygen cylinder pressure and monitoring the same at the monitoring station, it is required that the data should be transmitted using wireless communications rom the transmitter module to the receiver module. _Fcommunication is used for this purpose. This _RF

module comprises of a RF Transmitter and a RF Receiver.

The transmitter/receiver (TxlRx) pair operates at a requency of _{434 MHz.} A _F transmitter receives serial data and transmits it wirelessly through F at its antenna connected at pin4 (HT640). The transmission occurs at the rate of lKbps - 10Kbps.The transmitted data is received by a F receiver (HT648) operating at the same requency as that of the transmitter.

V. PROBLEM STATEMENT

The output of data conversion unit is voltage coresponding to the pressure at nozzle of the oxygen cylinder. The objectives of the proposed technique are as follows:

1. Process the signal from amplfier and display the pressure of oxygen ylinder.

2. Activate buzzer once the pressure in the oxygen cylinder drops below the predefined level

3. Communicate with the monitoring station using wireless communication.

4. Disply the pressure of all oxygen ylinders in use present in the hospital At the monitoring station utilizing Lab VIEW plaform.

VI. PROBLEM SOLUTION

The objectives mentioned in the previous section are caried out by using steps in the block shown in Fig 2 and Fig 3. It is clear rom Fig 2 that the signal corresponding to the oxygen pressure is sensed by a high precision MEMS pressure sensor.

The output of MEMS pressure sensor is ampliied using a non inverting ampliier and is fed to the micro-controller for processing. Here PIC 16F877 micro controller is used [7]. The unctions of the PIC micro-controller can be summarized as given below:

l. The signal rom ampliier is connected to the analog pin AO and reference to pin A2 of micro-controller.

2. Convert the analog signal to 8 bits digital signal using an inbuilt ADC. The digital data is now available in ADRESL

3. Move the digital data to W register and compare the data with the lookup table to compute the actual pressure.

The look up table is initialized by the user which gives

the relation between the digital output of the ampliier and the display data corresponding to actual pressure.

4. Initialize the LCD display connected on Port B (BO-B2) and Port D (DO-D7) to display the actual pressure.

5. Compare the digital data with the preset lower limit and if found less, activate the buzzer connected on the Port B5 through a relay.

6. Convert the data corresponding to pressure into serial data using USART register and transmit through _F module connected through Port C6 and C7.

The circuit board is tied with the oxygen cylinder. The power for this circuitry is derived rom a battery source. Since the oxygen cylinder is portable. Now if the battery is completely discharged, the whole system will not unction and will not serve the purpose. So two LED which gives indication about the battery are used on the board. If green the battery is good and if red the battery need to be replaced.

The transmitted data rom all oxygen cylinders in use are received at monitoring station using F receiver module. The monitoring station can be at nurse's duty room/ doctor's duty room. The status of oxygen level in all the cylinders in use are displayed at monitoring station for effective in time follow up actions. The proposed task at the monitoring station is caried out using LabVIEW platform. The LabVIEW platform consists of two panels, namely the ront panel and block diagram panel. The panel where the user can control or get the indications is known as ront panel and the block diagram panel where the actual program is coded. LabVIEW programs is not textual, these are program by the interconnections of palates (deined functional blocks). Fig. 6 shows a ront panel view of the proposed technique. Fig. 7 shows the block diagram view of program needed to achieve the proposed objectives [8],[9].

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OYGEN YUNDER PRESSURE

dab Port

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:0- Mesd Psre ¹¹j- : i-1.

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Fig 6. Front panel view of the display in the monitoring station

The ront panel consists of a 'start' button to control the initiation of the process and a 'stop' button to halt the process.

A string indicator 'measured pressure' which display the actual pressure, a visual display 'pressure indicator' to indicate the oxygen pressure are used. A waning text box which displays 'GOOD' when the oxygen pressure is in the prescribed range and 'CHECK' when the oxygen pressure is below the prescribed level are used in ront panel. A LED indicator glows when the oxygen pressure is less than the predeined level in the ront panel.

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= �"�o"""" �'''''"�. - ''''U." .. t_·

1M t"��_ T��!;"�_'_.o1 ^_^{I.. , ._}^i�

FIg 7. Block diagram view of the program in LabVIEW at monitonng statIon

The block diagram panel consists of palates which accept the serial data rom the F receiver module connected to the RS232 cable of the Pc. These data are then converted to parallel data. The pressure corresponding to these data is computed. Two indicators, one numeric and other tank type indicator are connected to display the actual pressure both in numeric and on visual mode. Further, this data is compared with the predeined level based on the outcome. A warning is displayed like GOOD or CHECK. A LED indicator to indicate the status of oxygen pressure in the cylinder is also connected.

All these unction blocks are placed in a while loop since the whole process should be carried out continuously. The condition for the while loop is given with the help of start button. There is a stop button to stop the process.

VII. RESULTS & CONCLUSION

The proposed measuring technique was subjected to test and the results were compared with the available pressure measuring instrument and tabulated in the Table l. The display at predeined level of oxygen pressure was set to 3.5 MPa the monitoring station is shown in Fig 8 and Fig 9.

Table I Result of the proposed measuring technique

SI.

No

2 3

Available Proposed

Instrument in technique in

MPa MPa

17.01 17.01

lO.35 10.35

3.25 3.25

I �:r .",.11: .^{.. ·,}.. , ''J' ", ) .• , ... . , I •• · ... ' . �v .. 1 ... . 1' ... ,,-1 •

Fil: ^Ct ^'Jw -r;:(1 p::te ^T:ob ^indo_ I:lp

� "]I13,�pli"""r.t I-��

OYGEN CYHDER PESSURE

Buzzer Off Off On

.tat

P�HLle Ind ::no·

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MeasurEd Presul! -j.'.-

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17.01 5

O

Fig S. Result shown on the front panel of the monitoring station when oxygen pressure is in prescribed rnge

=oJ;, ·�·i-- r-"o.". Of" ·' I" T, ,�� W""-,. H"'"

� �ll ·f .. ·"·;, .. ' .... F ... ·I�� ^•

OXYGEN CYNDER PSSURE data Port

Md Prrgllr8 3.25

1S ', -

STOP

W.Jrm·, .. \�.:

CII:CK

Fig 9. Result shown on the ront panel of the monitoring station when oxygen pressure is below the prescribed rnge

From Fig 8 and Fig 9, it is seen that the pressure of oxygen cylinder is monitored using numerical display and visual display. The unit of the numerical display can be set as per requirement of hospital staf. Visual display is very useul since it gives a feeling on the status of oxygen available in cylinder. On duty staff needs more attention when the time for replacement is knocking the door. A waning message as 'CHECK' along with a glow of LED indicates this critical time.

The results in table- l show that the proposed technique produces result which is matching with that obtained using a standard pressure measuring instrument. Buzzer was ON when the pressure level was less than the predeined value of 3. 5MPa. The user riendly display and alert at patient attendant's end and at monitoring station is expected to be highly beneicial to reduce the causalities due to non

replacement of oxygen cylinder at proper time.

Implementation of such a system at big hospitals and hospital where the ration between patient and nurses/doctors is high will be beneicial with respect to effective utilization of man power and life saving device.

REFERENCES

[I] Laurent Bertoletti, Patrick Mismeti, Herve Decousus, "Trends in Cause

Speciic Mortality in Oxygen-dependent", Am. J. Respir. Crit. Care Me. 2010; lSI: A3460.SX-150 Datasheet, Invensys sensor systems 2010.

[2] Hilary M. Womble, Richard P. Johnston, Richard M. Schwartzstein, David H. Roberts, "The Efect Of Supplemental Oxygen On Mximal Consumption Of Oxygen And Ventilatory Parameters In Chronic Obstructive Pulmonary Disease" Am. J. Respir. Crit. Care Me. ^2010;

lSI: A3572.

[3] Dr. Morris F. Keller, Kathryn Rose Mandel Keller, "Oxygen: A Critical Matter of Life-Support", Natural Healing Research Associates, 2007.

[4] "Oxygen Cylinders", Instruction manual, Wright & Filippis, Inc. 2001 [5] Hsu, "MEMS & Microsystems Design & Manufacture", Tata Mc-Graw

Hill Publication, 2002.

[6] C. J. Kauman, Rocky Mountain Research Lab., Boulder, CO, private communication, May 1995.

[7] PIC 16FS77 datasheet, Microchip Inc 2001

[S] Mhesh.L.Chugani, "Lab VIEW Signal Processing", Prentice-Hall India, 1995.

[9] National Instruments, LabVIEW Help Manual.