remote ch4 measurement final presentation[1] s 711

8/6/2019 Remote CH4 Measurement Final Presentation[1] s 711

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Jack Driscoll

PID Analyzers: Sandwich, MA 02563 ([email protected])

Kyungsue Han, Walter Johnson, Jiwoon Kim, Francesca Little, Pol Perov, Natalia

Perova, James Porter

Suffolk University: Boston, MA 02114 ([email protected])

Presented at Pittsburgh conference Paper # 250-45P 2009 #Pittcon
mailto:[email protected]:[email protected]


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ObjectiveOur goal was to develop and test a wireless methanedetection system for monitoring of methane

production in landfills and septic systems. Nitrogen

in septic systems is a problem on Cape Cod because

the majority of sewage is handled by septic systems.

We were interested in measuring methane levels

produced by septic systems to determine if sufficientquantities were available for capture and reuse in the

system to remove nitrogen.


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Methane Data Monitoring SystemDescription Schematic of system

The CH4 (combustible gas)sensor is connected to an

amplifier board which thentransfers the signal to a radiofrequency mote fortransmission to the basecomputer in a nearby building.

There is a solar powered batterybox that supplies poser to thesensor and amplifier circuit.The layout is shown in thediagram.


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System DescriptionSensor and Amplifier RF Crossbow Mote

The sensor head has a range of 0 to5% methane and constitutes half of

a Wheatstone bridge circuit. Theoutput voltage is about 10mV per% methane.

The second part of the bridge ispart of the amplifier board whichamplifies the differential signal by10 or 100 times (gain controlled bya switch). The output goes to aninput of the analog to digitalconverter board MDA300 which isattached to the Crossbow moteMICA2.

The microcomputer /RF transmitter(mote) sends data at 433 MHz to a basecomputer located in an office about 50m

away.

The mote is programmed to operate in alow-power mode in which it sleeps mostof the time (low power) and awakes every5 minutes for 30 seconds to takemeasurements and send data. It can run

several months on two 1.5 V AAbatteries.

The data packet from the mote containsthe mote battery voltage, humidity, andtemperature inside the mote box.


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Mote Box and Relay Control The mote and amplifier board are

enclosed in a weather-proof box

(see yellow box in figure) sitting

outside the septic tank. The sensor

head (inside the tank) is at the endof a 1 to 2 m 3 wire cable.

The amplifier together with the

sensor head, when activated,

draw 110 mA from a +6 volt battery

source but only 7mA from a -6 volt

source. This power is provided by

a solar powered battery box

connected to the mote box by a

cable (see diagram)

The MDA300 board attached to themote has several analog inputs and arelay that can be used to control thesensor circuit. When the mote wakesup to take data it closes this relay and

supplies 6 volts to other relays. Theserelays connect the +6 v and -6V to theamplifier and the sensor for 30seconds. (Response time of the sensoris 10 sec) At the end of this time, themote measures the output voltage ofthe amplifier, broadcasts the data ,

opens the relays to disconnect thebatteries, and goes back to sleep.

This mode of operation decreases thepower consumption of the board byabout a factor of ten compared tocontinuous supply of power.


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Solar Panel DescriptionSolar Panel Arrangement

Four solar panels, 3 x 5 , werefixed to the top of the battery box

to maintain the +6V and the -6Vneeded by the electronics. In fullsun, each panel can supply up to70mA at 7V. The largest drain wasthe +6V battery source so this wasmonitored using one of the analoginputs to the MDA300 board

attached to the mote.

The graphs show that the solarpanels are sufficient to keep thebatteries charged even in harshwinter conditions.

6V battery and mote battery voltages

0

1

2

3

4

5

6

7

6-Feb 11-Feb 16-Feb 21-Feb 26-Feb

Time

Voltage


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0

50

100

150

200

250

300

Sew

age(gal)

Time

Sewage Input vs Time (per day)


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0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

Feb-14

adc0 (v)

Sensor Voltage vs Time


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0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

adc0(v)

Time

adc0 (v) vs whole period


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Future plans

We will use a temperature controlled box with air (nomethane) to study changes in output voltage as a function

of temperature and time over a period of months. This will

allow us to check the drift of the sensor and determine the

time intervals needed for recalibration.

We will also place a thermocouple at the location of the

methane sensor as an additional input to the mote to

monitor ambient temperatures inside the septic tank. Thiswill help in understanding methane production inside the

septic system in different environmental conditions.


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ConclusionWe have developed and demonstrated a solar-powered

wireless methane data collection system. The data are

consistent with sewage flow conditions as stated by the

septic test facility. This device will allow the facility todetermine detailed behavior of different types of septic

systems and test the viability of collection and reuse of

methane to eliminate nitrogen from septic systems.

Acknowledgements: We are very appreciative of

the assistance of personnel at the Barnstable

County Alternative Septic System Test Center

remote ch4 measurement final presentation[1] s 711

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