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Moisture Content Measurement of Bark and Sphagnum Moss Using ECH 2 O Sensor for the Production of Phalaenopsis Wei Fang and Walter Ray Dept. of Bio-Industrial.

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Presentation on theme: "Moisture Content Measurement of Bark and Sphagnum Moss Using ECH 2 O Sensor for the Production of Phalaenopsis Wei Fang and Walter Ray Dept. of Bio-Industrial."— Presentation transcript:

1 Moisture Content Measurement of Bark and Sphagnum Moss Using ECH 2 O Sensor for the Production of Phalaenopsis Wei Fang and Walter Ray Dept. of Bio-Industrial Mechatronics Engineering National Taiwan University Taipei, Taiwan, ROC IHC01832

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11 Objectives  Find a sensor  Establish a water content monitoring system  Work on Sphagnum moss & bark

12 Why is it important to automatically measure water content in the media?  Skillful hand-watering personnel is not easy to find/ to train.  Hobby growers  professional growers  Increasing production area rapidly  Setting up foreign branch  Uniform quality requirement  …etc.

13 Many sensors available

14 ECH 2 O Soil Moisture Probes  Probe Type  Dielectric constant measurement  Measurement Time  10 ms  Resolution  m 3 /m 3 (0.1%)  Power  Requirements: 2.0 2mA to 5  Output: 10-40% of excitation voltage ( mV excitation)  Manufacturer:  Decagon Devices, Inc., USA

15 Campbell, 2004     ECH 2 OmV ECH 2 OmV  2500 mV excitation Converting eqs. provided by the manufacturer are for Soil only.

16 Soil type Sand, % Silt, % Clay, % EC ( mmho cm -1 ) Loamy Sand Sandy Loam Loam Silt Loam-A***0.2 Silt Loam-B Silty Clay Loam Silty Clay Campbell, soil types tested

17 Problem Converting equations for soil can’t applied to other growing media such as Sphagnum moss and bark.

18 雙層塑膠布屋頂 Data logger RI 1203 PC Loadcell Growth media w/ sensor (no plants) HID Lamp continuously on inlet ● ● Simulated greenhouse PE roof Indoor Experimental setup fan mV g / g

19 Conversion from gravimetric moisture ratio to Volumetric moisture ratio g water g media Bulk density m 3 water m 3 media

20 Bulk Density, g/cm 3 Orchiata Bark No. Bulk density Sp. Moss Bulk density NZ Loose Tight Chile Loose Tight China Loose Tight

21 Experiment of Pre-submerge  Before use  Treatment 1: Submerge the barks in water overnight (current practice of most growers)  Treatment 2: No pre-submerge (suggested by the manufacturer)  When use  After filled into the pot,  Watering thoroughly  Allow for drain out  Start recording the sensor output

22 Use it directly, do not submerge the bark in the water before use.

23 Difference due to pre-submerge in Tap water Orchiata bark #9Orchiata bark #5 Orchiata bark #8 w/ w/o

24 Small conclusions  Pre-submerge makes little difference for bark no.8 (smallest particle)  For large particle, without pre-submerge  Hold little water in the beginning  Dry out easily  Require frequent watering  If watering is conducted manually, pre-submerge will normally preferred.  wash-out of add-in Dolomite

25 Orchiata bark #9Orchiata bark #5 Orchiata bark #8 Difference due to pre-submerge in Tap water

26 Bark no.Eqs. R2R2 5 dby = x wby = x dby = x wby = x dby = x wby = x Converting equations derived for ECH 2 O-10 Note: y in g/g, x in mV; pre-submerged overnight

27 3 sources of Sphagnum Moss were investigated Imported from New Zealand (NZ) Chile China

28 Experiment of tightness of Sphagnum Moss filled in a pot

29 Preparation  Before use  Sphagnum moss was pre-submerged in tap water overnight  When use  Pressed until feeling moist not wet (hold with both hands)  Fill the pot with moist sphagnum moss  Watering thoroughly  Allow for drain out  Start recording the sensor output

30 Difference due to tightness of NZ Sphagnum Moss filled into a pot Photos taken after the experiment tight loose

31 Difference due to tightness of Chile Sphagnum Moss filled into a pot

32 Difference due to tightness of China Sphagnum Moss filled into a pot

33 Sp. Moss from Chile has the greatest water holding capability when loosely filled. When loosely filled, 3 types of moss performed quite differently. China Chile Difference due to sources of loosely filled Sphagnum Moss Sp. Moss from China has the greatest mV output due to high EC of dissolved water.

34 sources pHEC, mS/cm NZ Chile China Tap water NZChileChina

35 Small conclusions  Some SOPs are required to fill the pot when using Sphagnum Moss as growth media.  Fixed amount of Moss for fixed size of pot is preferred.  Tightly filled is preferred.  Water holding capability Chile > NZ > China Sphagnum Moss

36 ECH 2 O-10 vs. ECH 2 O-5

37 NZ Chile China Using ECH 2 O-10 in various EC range

38 Using ECH 2 O-5 in various EC range NZ Chile China

39 Small conclusion  ECH 2 O-5 sensor is less sensitive to EC variation, that make it a better sensor compare with ECH 2 O-10

40 Sphagnum MossEqs.R2R2 NZ dby = 0.024x wby = x Chile dby = x wby = x China dby = 0.018x wby = x Converting equations for ECH 2 O-10 on Sphagnum Moss Note: y in g/g, x in mV

41 Sphagnum Moss Eqs. R2R2 NZ dby = x wby = x Chile dby = x wby = x China dby = 0.024x wby = x Linear equations for ECH 2 O-5 on Sphagnum Moss Note: y in g/g, x in mV

42 Polynomial equations for ECH 2 O-5 on Sphagnum Moss Sphagnum Moss Eqs. R2R2 NZ dby = 1E-04x x wby = 8E-06x x Chile dby = 8E-05x x wby = 7E-06x x China dby = 7E-05x x wby = 6E-06x x Note: y in g/g, x in mV

43 Conclusions  ECH 2 O-10 and ECH 2 O-5 can be used to continuously monitor the water content of media used in growing Phalaenopsis. (ECH 2 O-5 is EC insensitive in the range of 0~2.21 mS/cm)  Converting equations were derived for 3 sources of Sphagnum Moss and 3 sizes of Orchiata bark.

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45 Thank you for your attention

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47 What is Permittivity ?  The permittivity of a medium is an intensive physical quantity that describes how an electric field affects and is affected by the medium.  Permittivity can be looked at as the quality of a material that allows it to store electrical charge. A given amount of material with high permittivity can store more charge than a material with lower permittivity.

48 What is dielectric constant ?  The dielectric constant ε r is defined as the ratio: ε r = ε s / εo = ε s / ( 8.85 x F/m) = ε s x 1.13 x  Where ε s : the static permittivity of the material in question, ε 0 : the vacuum permittivity. This permittivity of free space is derived from Maxwell's equations and is equals the ratio D/E in vacuum, where D is the electric flux density and E is the electric field intensity.  In vacuum (free space), the permittivity ε s is just ε 0, so the dielectric constant is unity.

49 Dielectric constant of some materials at room temperature MaterialDielectric constant Vacuum1 (by definition) Air Teflon2 Paper3 Soil Minerals4 Rubber7 Methyl Alcohol30 Water80 Barium Titanate1200


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