METS methane sensor MANUAL
Contents
1. METS methane sensor S N G51 E2783 MANUAL FRANA TECH UNDERWATER SENSORS FOR DISSOLVED GASES Franatech GmbH 1 2 3 4 METS User Manual Release Manual v9 2 1 April 2009 Sensor Parameters April 2010 CONTENTS METS Manual READ ME FIRST 1 1 WARM UP BEFORE DEPLOYMENT 1 2 DRY OUT BEFORE SWITCHING OFF 1 3 OPERATIONAL CONSTRAINTS se SRO 2 ae oe en ee oe N ee eee ane ate Rann eee anne ne Renee eee eee eee mae eee eee ASAE 2 1 5 CHEMICAL AGGRESSION MECHANICAL SPECIFICATIONS INPUT OUTPUT SPECIFICATIONS 3 1 PIN CONFIGURATION 3 2 CONSUMPTION 3 3 COMMUNICATION PROTOCOL FOR DIGITAL OUTPUT 3 4 CALIBRATION FORMULA MAINTENANCE 4 1 CHECK OF THE METHANE DETECTOR 4 2 SEALRINGS 4 3 CONNECTOR 4 4 CHECK AND REPLACEMENT OF THE MEMBRANE Contact Information Franatech GmbH Address for Delivery and Laboratory In der Marsch 8 21339 L neburg Germany Tel 449 4131 603884 Fax 49 4131 603885 Administration Weinbergsweg 19A 21365 Adendorf Germany email info franatech com URL www franatech com Franatech GmbH METS Manual 1 Read me first 1 1 Warm up before deployment After having been stored unplugged the semi co2. 2 Mechanical Specifications Dimensions en 37 Housing diameter 49 mm Length overall 200 mm Weight approx in alr 0 8 kg in water 0 5 kg Materials Titanium Housing and Connector Connector Subconn microcircular MCBH8M 3 Input Output Specifications 3 1 Pin configuration positive supply 9 36 VDC GND rex e sioalmetane SV male face view 7 TxD RS232 RxD RS232 Note both GND pins 2 and 6 are connected together on the electronic board temperature is measured inside the detector room 3 2 Consumption 115 mA 12 VDC switch on peak max 250 mA Franatech GmbH METS Manual 3 3 Communication protocol for digital output RS232 9600 Baud rate 8 Data Bits 1 Stop Bit no Parity Bit symbols used Carriage Return lt CR gt Space lt SP gt Command Query Sensor reply gt The sensor has a PIC address set at AO To read data send the command A0 lt CR gt Sensor reply gt 1 Methane lt SP gt 2 Temperature lt SP gt 3 Reserve lt SP gt 4 Reserve lt SP gt 5 Reserve lt SP gt 6 Reserve lt SP gt 7 Reserve lt SP gt 8 Reserve lt CR gt The output is ASCII Hex as raw data corresponding to voltage To convert to voltage value first convert from Hex to Decimal then multiply by 5 4096 Example Query A0 Reply gt 1 0AF2 2 07FB 3 0714 4 0000 5 0000 6 0000 7 0000 8 0000 The first value would then be OAF2 h 2802 d 2802 5V 4096 3 42 V 3 4 Calibr
3. 3 Connector According to manufacturer s recommendations ensure the connectors are lubricated the recommended lubricant is Molykote 44 Medium but use sparingly Half a match head dose per contact is adequate Franatech GmbH METS Manual 4 4 Check and replacement of the membrane The membrane serves for the desorption of dissolved gasses out of the surrounding water into the gas phase containing the detectors The diffusion is driven by Henry s Law The direction is conditioned to the concentration gradient between water and gas phase and within the membrane itself To clean the membrane it is not necessary to open the sensor Do not scrape the surface although the surface is quite robust it is advised to rinse with fresh water and eventually lightly dab with a fuzz free tissue oil free compressed air may be used Replacing the membrane is only necessary if damages like punctures or deep scratches are visible or if the membrane is folded over at the edge of the flange Eventual bulging is normal When replacing the membrane avoid any contact with the detectors avoid direct exposure of the detector room to dust humidity and particles Handle the membrane generally with care by holding it at the edge Notice after having been pressurized the membrane surface does not have a shiny appearance any more Gouges left by the seal rings are normal The membrane seal ring should be replaced if it looks deformed heavily flattened or show
4. ad Space method The concentration is calculated equivalent under standard 25 C 1atm The calibration is carried out at different concentrations generally 5 and temperatures generally 3 The conversion formula is obtained by a 3dimensional fitting between output voltage concentration and temperature The concentrations and temperatures are chosen first according to the ranges expected at the deployment location second according to the degree of resolution which is needed As a rule the wider the range the poorer the resolution Typical range limits are concentrations between 50 nmol l and 10 umol l and temperatures between 2 and 20 C The certificate with the calibration formula is provided on the next page Franatech GmbH METS Manual 4 Maintenance NOTICE opening the sensor except to replace the membrane without prior consulting and explicit authorization of Franatech leads to loss of guarantee 4 1 Check of the methane detector The detector is a semi conductor Adsorption of hydrocarbons on the active layer leads to electron exchange with oxygen and thus to modification of the conductivity of the active layer which the electronic converts into a voltage The following gives a simple method to control if the sensor needs a recalibration put the sensor in a bucket of methane free water and leave it always under power equilibrate at a room temperature of max 20 C When the displayed or output sensor temperatu
5. ation formula Basically the calibration aims at providing a relation between the sensor signal output and the concentration of dissolved methane lt is carried out in a dedicated apparatus which allows to prepare water with a known concentration of dissolved methane Gas mixtures of methane in air at different concentrations are bubbled in a reasonably air tight tank filled with water Calibration is started at lowest concentration in order to avoid having to change the water after each measure The water is circulated into a small chamber to which the sensor head is attached by means of a flange It is possible to have the sensor directly in the mixing tank however the water must be circulated or stirred by some means Otherwise a dead layer could build itself right before the membrane hampering methane diffusion This can induce an important delay before equilibrium is reached The different concentrations are obtained from commercial certified gas mixtures methane in synthetic air The water temperature is set at a definite value and maintained thermostatically For each concentration the measurement is made first when relative humidity has set around 100 and when equilibrium is reached between the partial pressures of methane in the gas mixture and in the water The signal output stays then level The time needed to attain this is conditioned to the size of the tank A water sample is taken and analyzed with a gas chromatograph using the He
6. hey resist to further drive then give eventually a further turn If you hear or feel grinding or creaking stop at once going farther might cause seizing or damage to the thread If the sensor is to be stowed unused for several weeks or months it is recommended to unmount the membrane rinse it dry it and if no damage is visible put it in place again as flat as possible
7. nductor needs several days to stabilize burning in process A rule of thumb is as many days of warm up as days of storage up to one week Beyond one week storage unpowered allow 7 days warm up whatever the storage duration This can be monitored by the methane voltage output evolution during warm up It is therefore recommended before field deployment to connect the sensor to the energy supply early enough prior to shipping and unplug it just for the shipping The sensor should be powered about 1 2 hour before being put to water To save power if the sensor is run on batteries during measurements it is possible to have the sensor warm up connected to the main supply then unplug it to connect to the battery supply The short interruption should have no influence The same goes after retrieval of the sensor if power has to be switched back to main If the sensor has been stored unpowered for several weeks it is recommended to have it lie powered minimum 6 hours in water in a bucket for instance after the warm up phase is completed The sensor is calibrated at 100 relative humidity Therefore the relative humidity should lie close to 100 This is reached about 30 min after the sensor is put into water the first time after a couple of days out of water If the sensor has been dry for a shorter period the humidity level is reached faster 1 2 Dry out before switching off After deployment it is recommended to let the sensor connected to
8. re has reached approximately 20 C the displayed voltage value for methane should be approximately for G51 E273 2 7V to 3 2V Values outside these ranges are signs of a probable drift if they are repeatedly observed To check the functionality of the methane detector use for instance a cigarette lighter Let gas flow against the membrane or against the detector for less than a second The signal should increase sharply within a few seconds Notice that a too long exposure to such high gas concentrations as in the lighter will drive the detector into saturation whereby it needs afterwards some time to return to background values NOTE As stressed in 1 a too long exposure might also causes a drift therefore the gas lighter check should be made only if there is a doubt regarding the sensor lt is recommended to recalibrate the sensor regularly Conditioned to deployment conditions we recommend between 6 and 12 months in some cases the sensor stays stable for a longer time than 12 months The semiconductors are ageing depending on stress extremely variable conditions of temperature humidity gas composition methane concentrations off on time The calibration should be carried out by Franatech as it disposes of the qualified personal and equipment No guarantee can be given for calibration carried out by the user himself 4 2 Seal rings Only the flange side seal ring should be lubricated see membrane replacement 4
9. s wear or cracks To replace the membrane proceed as follows loosen the 6 flange screws metric M3x8 Leave the head screws in place do not loosen them remove flange screws leave head screws remove the flange by prying it open carefully At the beginning it might be hard to pull after a few mm once the first seal ring appear it pulls out easily Avoid slanting Franatech GmbH METS Manual Turning the sensor downwards allows all parts to fall out flange screws sintered disc support disc The flange has a side seal ring and a membrane seal ring membrane seal ring side seal ring note only the side seal rings should be lubricated The membrane seal ring should absolutely be mounted dry Wipe the inside of the head room carefully to remove grease and water drops Be extremely careful not to touch the detector or let particles dust or water touch the sensor wipe inside the head room carefully Franatech GmbH METS Manual Put back in place first the support ring then the sintered disc and finally a new membrane Place the membrane as flat as possible smooth with finger is possible Align the flange to have the indentation covering the 3 head screws Press the flange evenly gently down until it sits avoid slanting Take care to tighten the flange screws crosswise to avoid slanting Notice Do not overdrive The screws should be driven to the point where t
10. the energy supply for about 15 min before unplugging it If the sensor has to be packaged extend to 30 min to ensure that no humidity gets trapped into the detector room 1 3 Operational constraints Maximum deployment depth is 4000m pressure tested at 480 bar Depressurization recommended max vertical soeed or pressure change rate 2 m s or from 250 to 1 bar in 20 30 min Operational temperature range 2 C to 60 C Response Reaction time 5 to 10 sec too time 5 to 30 min dependent on turbulences 1 4 Storage By risk of freezing store dry packaged DO NOT USE SILICA GEL Protect the membrane which must be free of scratches and punctures 1 5 Chemical aggression The following is valid for conditions underwater in the laboratory and also during work on deck Exposure to 1 H2S in air causes detector breakdown Exposure at 300 vppm H2S in air causes a signal equivalent to 10 vopm methane in air Below this no significant interference Avoid exposure to silicone adhesive soldering vapor hair grooming material hydrocarbons lubricants oil and fuel which might result in a drift of the detector Avoid long exposure to methane concentration above 10 umol l Beyond 1 2 hour at this concentration the sensor might need a couple of hours to recover This depends on the age and stress history of the detector Longer exposure in particular at or beyond saturation level can cause a drift Franatech GmbH METS Manual
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