Universities of Leeds, Sheffield and York

Transcription

1 promoting acce to White Roe reearch paper Univeritie of Leed, Sheffield and York Thi i the author pre-print verion of an article publihed in the IEEE Senor Journal White Roe Reearch Online URL for thi paper: Publihed article: Hobby, MJ, Thoma, RE, Gacoyne, M, Paron, DR, Keevil, GM, Peakall, J and Carrivick, JL (2013) MEMS-integrated load cell for meauring preure, eroion, and depoition in dynamic environmental flow. IEEE Senor Journal, 13 (2) ISSN X White Roe Reearch Online eprint@whiteroe.ac.uk

2 MEMS Integrated Load Cell (MILC) 1 A MEMS Integrated Load Cell (MILC) for meauring preure, eroion & depoition in dynamic environmental flow M J Hobby, R E Thoma, M Gacoyne, D R Paron, G M Keevil, J Peakall, J Carrivick Comment [JLC1]: Peronally I think that the ue of acronym in title i to be avoided. Comment [JLC2]: I thi ymbol ued/permitted in the target journal? I would have thought that and would be more appropriate. Abtract A MEMS Micro Electro-Mechanical Sytem-baed load cell ha been integrated with ignal conditioning circuitry, temperature and tilt enor for meaurement of ediment-fluid interaction and flow under turbulent condition. Such an intrument i of great value for improving undertanding ofquantifying turbulent flow and ediment dynamic within flood event and river or coatal eroionetting, for example. Senor enitivity wa teted to a ma of 0.5g but can be hown theoretically to extend to 50mg. The enor wa found to have no attenuation of frequencie up to 2.5Hz and would therefore be uitable for monitoring turbulent flow. Laboratory flume experiment, imulating a dam burt, demontrate the applicability of the enor for meauring highly dynamic and tranient flow phenomena in unprecedented detail. Index Term MEMS, flood, eroion, flow, load cell, environmental monitoring M I. INTRODUCTION EASURING turbulent flow propertie uch a dynamic fluid preure, hear tree, and the aociated eroion, tranport and depoition of particle at the fluidediment interface i of paramount importance for advancing our knowledge of a range of complex environmental flow, uch aincluding thoe that occur during avalanche, debri flow, flood or longer-term and/or larger-cale event Error! Reference ource not found.[6], [5][7], [8][8]. However, ucceful monitoring of uch patially-ditributed procee over the range of relevant temporal cale i notoriouly difficult. Exiting laboratory-baed technique including acoutic [14] or laer [11] Doppler velocity probe, echoounder [2], terretrial (ground-baed) LiDAR and cloerange photogrammetry [3] generally capture only either patial or temporal variability and have to neglect the other dimenion. Thi focu on a ingle dimenion can introduce ignificant uncertaintie when attempting to quantify fundamental procee in ytem that exhibit coincident and/or concurrent patio-temporal change. In addition, the preure field and/or the hear tre exerted at the flowediment interface ha often only been etimated through extrapolation of in itu velocity meaurement [5], and to date, preure tranducer or electrical conductivity probe [12][13] have only captured gro bed-ediment tranport rate [1] or preure on tatic concrete lab [12]. Recent advance in Micro Electro-Mechanical Sytem (MEMS) now enable the contruction of load cell array at the laboratory cale with potential to meaure the dynamic preure induced by turbulent flow and ediment tranport procee. Herein, we preentthe aim of thi paper i to preent the development and initial application of a ingle MEMS Integrated Load Cell (MILC). MEMS load cell-baed laboratory device. The MILC that ha i been integrated with an accelerometer and a thermitor, to make upporting obervation of enor orientation and temperature, repectively, and wa combined with low noie ignal conditioning electronic and encloed within a mall-footprint intrument houing. Thi In order to demontrate the deign of the device i and it capability capable of obtaining very detailed patio-temporal proce information at the edimentflow interface,. The intrument ha been termed the MEMS Integrated Load Cell (MILC). In the preent paper, we herein: firt i) outline the deign of the intrumentation. Second, we, ii) decribe initial tet and calibration. Third, we, iii) demontrate the quality and validity of laboratory flume data obtained uing the device. Finally, we, iv) outline potential extenion of the deign and ugget avenue for deployment that will help improve our ubtantive undertanding of geophyical flow. II. INSTRUMENT OVERVIEW The rationale behind the Scientific pecification of a enitive and accurate preure enor device for laboratory application mainly concern the deirei abolutely neceary for for thequantification of the mallet patio-temporal reolution of preure meaurement while whilt till allowing the broadet poible application range. To enable the detection of turbulence-induced fluctuation of preure, the an intrument mut be capable of meauring preure variation < 1 Pa active over a patial extent < 2000 mm 2 and at a ampling rate > 20 Hz. In mot environmental fluid dynamic laboratorie, the maximum operating depth of water i of the order of 1m and therefore, the intrument mut alo be capable of meauring maximum tatic loading of ~9810 Pa. Finally, the intrument mut be rugged, reitant againt impact and abraion and capable of operating reliably over a range of temperature condition in electrically noiy environment. A. Principle of Operation The laboratory intrument decribed herein meaure the Comment [JLC3]: I do not know what thi acronym i, which i not helpful becaue the abtract hould tand-alone. I have inerted the full definition Comment [JLC4]: I it correct for the target journal to lit reference alphabetically, becaue thi reult in thee citation number being out of equence in the manucript? i.e. I would expect number 1 to be firt! Comment [JLC5]: Rather vague can we quantify what hort time-cale we are talking about?

3 MEMS Integrated Load Cell (MILC) 2 weight of a column of fluid and/or ediment directly above a MEMS load cell. The load cell itelf meaure the force acting upon a plate of fixed area. The meaured load i thu directly proportional to the preure. which wa choen due to it low drift propertie. The Honeywell FSS erie ue piezo-reitor in a Wheattone bridge configuration. The piezo-reitor are machined from ilicon and actuated directly by a tainle teel ball. The nominal reitance of the bridge wa meaured to be 4.6kΩ. The differential bridge output i reported to range from 0.12mVg -1 to 14mVg -1 and therefore need to be amplified before digital converion (Fig. 2Fig. 2). SPI Fig. 1 - Meaurement principle behind the MEMS Integrated Load Cell (MILC), demontrating the combined meaurement of fluid and ediment Within the context of an experimental flume facility, the total preure meaured by the load cell, P T, ha two component: the preure due to the ediment (if any) within the flume, P, and the preure due to the fluid, P f (Fig. 1Fig. 1): P P P T f Note that the term fluid doe not differentiate between purely clear-water flow and water containing a finite amount of upended matter. P i dependent on the thickne of ediment within the column (h ), the aturated bulk denity of that ediment (ρ ) and the gravitational contant (g): P h g Similarly, P f i dependent on the total height of the column (h T ) and the fluid denity (ρ f ): Pf ht h f g Auming no intantaneou change in the water urface elevation, when ediment i eroded the volume of ediment in the meaurement column reduce and the volume of water increae by an equal amount. Converely, a ediment i depoited, the volume of water in the meaurement column reduce and the volume of ediment increae by an equal amount. Defining the change in the thickne of ediment, Δh, a poitive for eroion and negative for depoition, the change in preure, ΔP, caued by Δh can therefore be decribed by: P g h g h f g h Dynamic variation in preure can thu be meaured and the thickne of ediment inferred. B. Electronic Sytem Deign The ytem i baed around a Honeywell FSS erie load cell, f RS485 RX RS485 TX Fig. 2 Schematic block diagram of the MILC The differential ignal from the load cell i amplified uing an intrument amplifier. The gain of the amplifier i et to 25.7 uing tandard value reitor with a low temperature coefficient, maintaining conitent gain acro the temperature range. The gain i et to maximize enitivity while enuring the amplifier i not aturated prior to the load cell reaching it maximum load. A imple low-pa (LP) filter i ued to minimize aliaing ditortion and maximize ignal-to-noie ratio. The breakpoint of the filter i et to ~160Hz, o a to be above any frequency of interet. Preciion component were not ued in the filter ince the breakpoint wa choen relatively arbitrarily. To enure the ADC input wa not overloaded (which would caue fatal damage to the ADC), a Schottky diode clamp to the digital poitive rail (+5V) wa ued. Maximum linear headroom wa achieved by uing a diode with a low turn-on voltage. The load cell and ADC are both fed by preciion voltage reference, which can be adjuted uing preet reitor during the calibration proce. Two additional enor have been incorporated within the deign. Firt, a MEMSIC dual-axi accelerometer, the axe of which are aligned with the horizontal, i included to enable the MILC intrument to be oriented at angle other than normal to the gravitational field vector. Thi accelerometer wa elected becaue of it mall form factor, requiring le circuit board pace. Second, a Betatherm thermitor bead ha been placed a

4 MEMS Integrated Load Cell (MILC) 3 cloe to the load cell a poible to allow account to be taken of change in the mechanical repone of the load cell with change in temperature. Internal peripheral communication i carried out uing a Serial Peripheral Interface (SPI) bu. SPI bu mater and intrument control i carried out on an Atmel ATmega644 microcontroller, which ha an embedded 10-bit ADC. Thi wa conidered uitable for the temperature meaurement and accelerometer tilt meaurement but a higher degree of accuracy wa required for the load cell. Therefore, an ADI AD7680 ADC wa ued, due to it availability in a mall form factor (SOT-23 package). The Effective Number of Bit (ENOB) of thi device i ~ The circuit deign wa plit acro two circuit board: the analog ignal conditioning and the digital proceing. Thi wa done to minimize noie and interference from the high peed witching of digital communication line. The ADC wa placed on the analog ignal conditioning board, which communicated with the digital board uing SPI. Special care wa taken to minimize the effect of interference from thi ource by careful routing of digital ignal return path. Analog and digital ground were kept apart and linked at one point, cloe to the power input. The dual-deck circuit board are hown in Fig. 3Fig. 3. Digital proceing PCB Analog ignal conditioning PCB Fig. 3 Dual-deck approach to the circuit deign to minimize noie and interference from high peed digital communication line. The cale i in centimeter. An array of MILC i required to make patially-ditributed meaurement of preure, and thu turbulent velocity fluctuation, and/or eroion and depoition of ediment. Data from each MILC mut be ynchronized to other unit in the array. A real-time data logger i therefore ued to gather data from the array, with individual MILC attached to a RS485 bu. MILC unit are addreed individually in oftware uing a node ID. When not driving the bu, the MILC driver witche to high impedance, freeing the line for other intrument in the array. A DataLink layer wa defined to it above the Phyical layer provided by the RS485 tandard a hown in Fig. 4Fig. 4. Communication i initiated with a tart bit equence followed by 5 bit for the actual command. The econd byte i alway the node ID. An ID of 0 indicate a broadcat command. All intrument in the array are intructed to perform a meaurement uing a broadcat command with data being ubequently collected by a pecific addreed command. Fig. 4 Data communication packet tructure ued in MILC DataLink layer C. Mechanical Deign The MILC i preently houed inide a 29mm radiu cylindrical hell that i plit into five ection (Fig. 5Fig. 5). Particular attention i drawn to the rubber diaphragm, which i clamped in place by the top flange and form a watertight eal with the main hell. Thi diaphragm provide the contact between the fluid outide the intrument and the load cell. To maximize enitivity to load variation, bra plate are affixed to the top and bottom of the center of the diaphragm to locally increae it tiffne. The edge of the diaphragm are free to move o that change in load above the top plate are tranmitted a faithfully and quickly a poible to the load cell. The circuit board fit nugly inide the outer houing, but a crew fed from the bottom of the intrument prevent any lack in the ytem. In addition, becaue thi crew drive the circuit board, and therefore the load cell, into the diaphragm it can alo be ued to manually tare the intrument and enure that the load cell i within it linear operational range. The crew head i covered by a cap which i ealed with an O-ring. Cabling feed through the bottom flange and watertight eal. An O-ring i ued to eal the bottom flange to the main hell, with ix crew clamping it in place. The top flange, main hell and bottom flange are preently contructed of bra, owing to it availability, trength and reitance againt abraion within harh laboratory condition. Thi hell ha been teted in up to 1m deep water with no ign of water ingre. Modern polymer are an attractive alternative to bra becaue they provide imilar trength propertie, ignificant material cot Formatted: Default Paragraph Font

5 MEMS Integrated Load Cell (MILC) 4 aving and permit rapid ma-manufacture uing injectionmolding procee. III. TESTING THE ANALOG CIRCUITRY DESIGN A erie of tet were conducted to enure that the amplitude repone of the ytem wa linear, the frequency repone wa above 20Hz and noie wa minimal. Two different methodologie were adopted. Firt, the ignal conditioning circuitry wa modeled in SPICE oftware (National Intrument MultiSim) to imulate the amplitude repone, frequency repone and output noie. The load cell wa modeled a a Wheattone bridge with all reitance et to 4.6kΩ. Preciion voltage reference were modeled a perfect voltage ource in erie with a thermal noie ource producing the ame level of noie a quoted in the component dataheet, and the amplifier wa modeled uing the SPICE model upplied by it manufacturer. Second, phyical tet were conducted on a prototype, a per the final dual deck deign, to identify amplitude repone and output noie. During thee tet, the load cell wa removed from the circuit board and imulated uing a Wheattone bridge of 4.6kΩ reitor. One reitor in the bridge wa replaced with a variable reitor to adjut the output of the bridge. A. Amplitude Repone Both teting methodologie were employed to tudy the amplitude repone of the load cell ignal conditioning circuitry. Uing the firt modeling method, the output of the load cell wa monitored a the reitance of one reitor in the bridge wa adjuted. Thee tet clearly identified the linear region of the amplifier between floor and ceiling point at ~0.7V and 5.1V, repectively (Fig. 6Fig. 6 circle ). The clamping diode did not caue any degradation of linearity up to 5V (maximum poible input value of ADC). The econd prototype method demontrate the ame linear repone, extending lightly lower (Fig. 6Fig. 6 croe ). Bra top flange, held in place with ix CSK crew. Top plate and rubber diaphragm. Provide watertight eal. Tranfer external load to internal load cell. Bra enor hell. Square channel machined out from inide to ecurely houe circuit board Rubber O-ring between hell and bottom flange to enure watertight eal Fig. 6 Modeled (o) and prototyped (+) analog ignal conditioning electronic circuitry demontrating the linear operation, within limit, of the MILC front end. The input load cell wa imulated uing reitor in a Wheattone bridge configuration. B. Frequency Repone To tudy the frequency repone of the intrument, the modeling method wa ued. An AC ource wa placed in erie with the Wheattone bridge, with one reitor et lightly lower than the other to produce a DC offet. The AC ource wa wept from 0.1Hz to 500Hz. The imulated amplitude and phae repone are hown in Fig. 7, demontrating flat repone in exce of 20Hz. Bra bottom flange, held in place with ix CSK crew. A locating crew act through center hole to force circuit board, and therefore load cell into contact with diaphragm. Bra cap to eal locating crew. Rubber O-ring enure watertight eal Fig. 5 Schematic of mechanical layout of the MILC

6 MEMS Integrated Load Cell (MILC) 5 to infer a maximum load of 584g at 5V. Uing the known urface area of the top plate (506.7mm 2 ), the denity of water at 10 C (999.7kgm -3 ) and the gravitational acceleration (9.807m -2 ), thi MILC unit i therefore capable of meauring preure in water column up to 1.15m deep. The adjutment crew could be looened to obtain a greater range, at the rik of operating outide the linear region for mall weight. Greater range can alo be achieved by decreaing the amplifier gain, which in turn decreae reolution. Fig. 7 Modeled normalized frequency repone of analog ignal conditioning circuitry, demontrating flat repone up to 20Hz (indicated vertical by the dahed line). C. Noie Both teting methodologie were employed to tudy the noie introduced by the ignal conditioning circuitry. The noie wa invetigated at the point the ignal conditioning circuit connect to the ADC. The model predicted a total output noie of 33.3μV rm. Converely, 25,000 meaurement of voltage (taken at 1Hz) made from the prototype yielded a total output noie of 650μV rm. The difference i thought to be due to an overimplification in the model. A. Calibration- Voltage againt Temperature A noted previouly, it i known that the mechanical repone of load cell i temperature-dependent, thu neceitating the incluion of a temperature enor to calibrate the ytem. To characterize thi changing repone and thu quantify the calibration required, the MILC wa firt placed in an ice bath to decreae it temperature. The intrument wa then removed and both output voltage and temperature were logged a the intrument warmed to room temperature. The unit wa then heated to 50 C. Output voltage and temperature were logged a the intrument ubequently cooled to room temperature. Raw load and temperature data from both experiment were concatenated and filtered uing an 8-point moving-average filter, to minimize random noie in voltage and temperature ignal. IV. CALIBRATION & TESTING A. Calibration- Load againt Voltage To calibrate the MILC, a range of calibrated weight (500g, 200g, 100g, 50g, 20g, 10g, 5g, 2g, 1g, and 0.5g, equivalent to preure of ~9680Pa, ~3870Pa, ~1940Pa, ~968Pa, ~387Pa, ~194Pa and ~96.8Pa, repectively) were placed on the MILC and ~700 data point were collected at a frequency of 100Hz. The adjutment crew wa tightened until the MILC output increaed above 0.7V, demontrating that the load cell wa in contact with the diaphragm and the unit wa operating in it linear region. Data wa averaged acro all the point for each load and plotted againt the applied load (Fig. 8Fig. 8). Linear regreion yielded coefficient of determination, R 2, cloe to 1.0 for all intrument teted. Small load caued a greater pread about the linear fit. Thi i due to the decreaed load not diplacing the bra plate of the intrument to a large a degree a greater load. Further tet were carried out uing a fixed load to bia the intrument and then adding maller load. The coefficient for each individual MILC varied lightly, with an average lope of 151gV -1 (±6gV -1 ) and offet of 171g. The variation in lope i due to the tolerance in component value and remain fixed for an individual MILC ytem. The variation in offet i caued by the adjutment crew, which i ued to enure the unit i operating within the linear region of repone, and can be adjuted between experiment. The data obtained in thi tet can be extrapolated Fig. 8 Applied tatic load (in gram) againt MILC meaurement (in Volt).

7 MEMS Integrated Load Cell (MILC) 6 Fig. 9 Variation in MILC output with varying temperature. The linear bet fit line i hown a the white line. Data wa gathered from two experiment where the MILC wa allowed to return to room temperature from either operational temperature extreme. Limited data wa obtained between approximately 28 C and 38 C. Linear regreion characterized the relationhip between temperature, T, and change in meaured voltage, ΔV, a (white line; Fig. 9): V T The coefficient of determination for thi fit (R 2 ) i B. Noie The total ytem noie, ε T, i given by: T i q R 2 =0.97 ΔV= T where ε i i the noie at the input to the ADC (650μV rm; IIIC) and ε q i the root mean quare error in the ADC, given by [9] a: V f 1 2 q 12 2 ENOB where V f i the full range of the ADC (5.0V) and ENOB i the Effective Number Of Bit, which can be calculated from the information within the dataheet to obtain ~13.83 [10][9]. ε q i therefore found to be 99.1μV rm and ε T i 658μV rm. Following calibration, it i known that the load cell output change by ~330μV for a 50mg change in applied load (~0.97Pa change in preure). Thu, noie i the limiting factor in the enitivity of the MILC to preure fluctuation. To oberve the required voltage level below the level of noie, the noie mut be diminihed through overampling. Thi ha the additional benefit of increaing the ENOB and hence increaing the reolution. Overampling ha therefore been implemented onboard the MILC intrument, inviible to the uer, producing a ingle average reult baed on a number of ample. Overampling onboard the MILC intrument ha the advantage that RS485 traffic i minimized. Converely, overampling onboard ha the diadvantage that the MILC become unreponive for the time to take a ingle ample (~2.5µ) multiplied by the overampling factor. The overampling factor invoked by the MILC can be et to a power of 2, from 2 0 up to 2 10 (1024), o a to enable diviion via a imple bit hift. Total noie diminihe a: 1 T N T 0 N where ε T (N) i the total noie with an overampling factor of N and ε T (0) i the total noie with no overampling. Thu, with the overample factor et to 64 (2 6 ), the noie diminihe to 82μV rm, equivalent to ~12mg change in load (~0.23Pa change in preure). Uing the maximum overample factor of 1024, the noie can be further reduced to 20.5μV rm. With thee level of electronic noie, the repone of the intrument i dominated by the mechanical tructure of the hell. However, ince the return packet data i limited to 2 byte the ENOB cannot be greater than 16, equivalent to an overample factor of Thi i achieved by the MILC with an overample factor of 32 (2 5 ) [10]. Further increae of temporal reolution can be obtained by requeting more ample from the MILC within a given time period. However, thi reult in a compromie on the overall data throughput, which i dependent on the maximum frequency of data required or the number of MILC intrument on any ingle RS485 bu. C. Frequency Repone To quantify frequency repone of the MILC, the intrument wa placed at the bottom of a graduated cylinder with an internal diameter of 73mm and a peritaltic pump wa ued to firt fill and then empty the cylinder at variou rate. The pump outlet wa clamped a few millimeter above the center of the top plate of the MILC in order to limit tube motion that might induce water motion in the cylinder and therefore periodically diturb the water urface. Fig. 10 Time erie data, howing the MILC and pump tachometer data while the pump output i directed toward the top plate of the MILC.

8 MEMS Integrated Load Cell (MILC) 7 MILC data. Thee are hypotheized to be due to the pump tachometer proceing and do not repreent real ocillation in the cylinder. Fig. 11 Comparion of data in the frequency domain between the MILC intrument and a peritaltic pump delivering pule of water onto the top plate of the MILC at a rate of 2.5Hz. Tachometer data i offet in the y-axi to enable clearer comparion. The Waton-Marlow peritaltic pump employed herein i readied for ue by clamping pecially-manufactured ilicon tubing full of water inide a circular pump caing. A a cam haft fitted with three roller rotate at a uer-configurable rate (in revolution per minute), the tubing i compreed againt the caing and water i forced to move through the tubing. Thu, by etting the revolution rate to 50rpm, the three doe that are outputted per pump haft revolution yielded a doage frequency of 2.5Hz. A digital tachometer on the cam haft that produce 343 pule for every revolution wa ued to monitor the fractional rotation of the haft. To enable comparion of data from the MILC and the tachometer, their output were logged ynchronouly with a National Intrument Compact RIO real time logging computer. The voltage-temperature calibration of the unit ( IVB) wa applied to the MILC data, and then the data from a ingle fill cycle were linearly detrended to remove the overall trend of increaing load. A the cylinder filled, the magnitude of the load fluctuation detected by the MILC diminihed over time (Fig. 10), a the preure impoed by each doe of water became a maller and maller fraction of the total hydrotatic preure of the water in the cylinder. To identify and compare the main ytem harmonic, both dataet were ubjected to a Fat Fourier Tranform (Fig. 11). Note that the tachometer data ha been offet on the y-axi to facilitate comparion. The 2.5Hz fundamental can be clearly een in both the tachometer and MILC output, with no decreae in amplitude (Fig. 11). Although thi tet cannot prove that the MILC repond at it target pecification (20Hz) owing to limitation of the peritaltic pump, it i not unreaonable to expect to be able to monitor turbulent load/preure fluctuation within the frequency meaurement made. Needle to ay, variation will be averaged acro the vertical column. There are two further ub-harmonic at lower frequencie in the tachometer data that are not apparent in the V. INITIAL RESULTS With MILC ytem characteritic fully quantified, the ytem wa deployed and teted during flume experiment conducted at the Sorby Environmental Fluid Dynamic Laboratory (SEFDL) at the Univerity of Leed. Following [4][5], a imple dam-break et-up wa contructed within a m (l w d) flume. Four MILC unit were intalled at downtream ditance of 1.5 and 2.5m from the a dam break releae lock gate. The MILC unit were poitioned at cro-tream ditance of 0.05 and 0.15m, repectively. To initiate dam break outburt flood, a gated lock-box wa filled to a depth of 0.5m with clear water. The lock gate wa then raied intantaneouly by 80 mm, permitting water to flow out from below the raied gate and acro the flume floor that wa uniformly covered in ~75mm of mobile fine gravel (median grain ize, D 50 = 5mm; [4]). At each downtream ditance, one MILC unit wa covered by a porou cap that permitted loading only by water, while the other wa loaded by both water and gravel. Each experimental run lated for ~30. Flow depth/head variation throughout the flood wave were recorded by the intrument. Flow were alo monitored through the flume wall with ide-looking high-peed 50fp video camera. The reult how the performance of the MILC in relation to the depth calculated uing the video camera record. Fig. 12 how the temporal variation of the total flow depth (h T ) or tage and the aociated temporal variation of the relative preure meaured by the MILC (note that the hydrotatic preure ha a component due to the water and the ediment in the ediment+water cae). A the flood front arrive, relative preure rapidly fall to le than hydrotatic in both the water only and ediment+water cae, before lowly recovering to (near) hydrotatic from ~3-4 after the releae of the lock gate. Thi rie i commenurate with the gradual decreae in water depth and flow velocitie following paage of the flood peak. The delay between flood peak arrival at 1.5m and 2.5m i clearly oberved. Comment [JLC6]: Should thi be [4]?

9 MEMS Integrated Load Cell (MILC) 8 Fig. 12 Temporal evolution of the tage (= total flow depth, h T) at 1.5m (a) and 2.5m (b) downtream. The relative preure of the outburt flood a it propagate acro a bed of fine gravel i hown for both ediment and water at 1.5m (c) and 2.5m(e). Relative preure for water only i hown at 1.5m(d) and 2.5m(f). Fig. 13 Temporal evolution of the tage (= total flow depth, h T) of the outburt flood at 1.5m(a), 2.5m(b) downtream and the aociated eroion a it propagated acro a bed of fine gravel, again at 1.5m(c), 2.5m(d) downtream. The inferred change in bed elevation aociated with the paage of the flood wave hown in Fig. 12 are highlighted in Fig mm of eroion i etimated to occur a the highly turbulent flood front pae the MILC, with ediment tranported from uptream almot completely in-filling the ediment bed following paage of the flood front. Net eroion i etimated to be 1-3mm. However, while whilt our obervation ugget that the latter etimate i realitic, the maximum cour depth do not appear to be o. We hypotheize that thi i either caued by change in the poroity of the ediment bed, cauing (unmeaured) change in it bulk denity or more likely to the generation of a quaiuction effect during the paage of the highly turbulent flood wave, reducing preure to le than hydrotatic. The latter hypothei i upported by preure meaurement on immobile bed. VI. SUMMARY Thi paper ha preented the development and teting of a novel MEMS baed enor capable of recording micro-cale preure variation in geophyical flow in a laboratory etting. The linearity, noie and frequency repone have been quantified and found to be within, or cloe to the initial pecification. In it current form, the MILC ha been hown to be capable of recording the depth/head variation of a dambreak outburt flood flow at high temporal reolution and to a high degree of accuracy. It The development and application of MEMS load cell i of particular importance ince the reduced (and, with continuing technological advance, reducing) ize of uch enor could potentially increae the patial reolution of meaurement to the order of 1mm while retaining their temporal reolution (>100Hz). Both of thee pecification improve upon preently available technologie uch a X and X. The larget phyical element of any MEMS enor tend to be the houing that enable integration with other component. The ucceful demontration of a ingle MEMS enor to meaure particulate flow i an important tep toward realizing many load cell on a ingle ilicon ubtrate for example. The further extenion of the preent work from ingle enor to large array of enor hold ignificant promie for enabling improved undertanding of the mot complex geophyical and edimentological flow. We therefore conider that MILC ha have ignificant potential for examining ediment tranport procee and quantifying the patio-temporal extent of eroion and depoition induced by a range of geophyical flow. It The relatively low power of operation (le than 0.5W), together with it rugged, waterproof houing, mean that imilc t alo lend itelfwill alo be uitable to for long-term field intallation a well a the laboratory application imilar to thoe preented herein. The A MILC may could alo be ued to examine other type of particulate flow and capture the dynamic of bedform migration in and and/or gravel, examine the detailed dynamic of turbidity driven current, or indeed examine now avalanche and/or the impact of raindrop/hailtone on the Earth urface. The development and application of MEMS load cell i of particular importance ince the reduced (and, with continuing technological advance, reducing) ize of uch enor could potentially increae the patial reolution of meaurement to the order of 1mm while retaining their temporal reolution (>100Hz). Both of thee pecification improve upon preently available technologie. The larget phyical element of any MEMS enor tend to be the houing that enable integration with other component. The ucceful demontration of a ingle MEMS enor to meaure particulate flow i an important tep toward realizing many load cell on a ingle ilicon ubtrate for example. The further extenion of the preent work from ingle enor to large array of enor Comment [JLC7]: Our meaurement? Or omeone ele? Formatted: Indent: Firt line: 0.36 cm Comment [JLC8]: Plu it i virtually non-invaive, compared to other method? Comment [JLC9]: Thi paragraph i a bit rambling, and pecific to the deign of the MILC I would trim it down and I have moved it upward to place it firt in thi ummary ection, o a to finih with the mot hard-hitting real-world application tuff Comment [JLC10]: A bit random not part of the geophyical flow type phenomena poken about earlier I ugget delete Comment [JLC11]: Plu it i virtually non-invaive, compared to other method?

10 MEMS Integrated Load Cell (MILC) 9 hold ignificant promie for enabling improved undertanding of the mot complex geophyical and edimentological flow. REFERENCES [1] Bergman, N., Laronne, J. B. and Reid, I., Benefit of deign modification to the Birkbeck bedload ampler illutrated by flahflood in an ephemeral gravel-bed channel. in Earth Surface Procee and Landform, 32: , [2] Bet, J. L. and Ahworth, P. J., A high-reolution ultraonic bed profiler for ue in laboratory flume. in Journal of Sedimentary Reearch A, 64: , [3] Butler, J. B., Lane, S. N., Chandler, J. H. and Porfiri, E., Throughwater cloe range digital photogrammetry in flume and field environment. in Photogrammetric Record, 17(99): , [4] Carrivick, J. L., Jone, R. and Keevil, G., Experimental inight on geomorphological procee within dam break outburt flood. in Journal of Hydrology, 408: , doi: /j.jhydrol , [5] Cou, R. and Well., M.G., A comparion of the hear tre ditribution in the bottom boundary layer of experimental denity and turbidity current. in European Journal of Mechanic B / Fluid, 32: 70-79, [6] Ernt, G. G. J., Spark, R. S. J., Carey, S. N. and Burik, M. I., Sedimentation from turbulent jet and plume. in Journal of Geophyical Reearch, 101(B3): , [7] Felix, M., Sturton, S. and Peakall, J., Combined meaurement of velocity and concentration in experimental turbidity current. in Sedimentary Geology, 179: 31-47, [8] Garcia M. H., Depoitional turbidity current laden with poorly orted ediment. in Journal of Hydraulic Engineering, ASCE, 120(11): , [9] Glover I. and Grant M., Digital Communication. Prentice Hall, 1024 pp, [10] Ket, W., ADC Input Noie: The good, the bad, and the ugly. I no noie good noie? in Analogue Dialogue, 40-02, [11] Liu, Z., Adrian, R. J. and Hanratty, T. J., Large-cale mode of turbulent channel flow: tranport and tructure. in Journal of Fluid Mechanic, 448: 53-80, [12] Melo, J.F., Pinheiro, A.N. and Ramo, C.N., Force on plunge pool lab: Influence of joint location and width in Journal of Hydraulic Engineering, ASCE, 132(1): 49-60, [13] de Rooij, F., Dalziel, S. B. and Linden P. F., Electrical meaurement of ediment layer thickne under upenion flow. in Experiment in Fluid, 26: , [14] Takeda, Y., Intantaneou velocity profile meaurement by ultraonic Doppler method. in Japan Society of Mechanical Engineer, International Journal Serie B, 35(1): 8-16, Comment [JLC12]: Thi paragraph i a bit rambling, and pecific to the deign of the MILC I would trim it down and place it firt in thi ummary ection, o a to finih with the real-world application tuff