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:
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
Objectives Find a sensor Establish a water content monitoring system Work on Sphagnum moss & bark
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.
Many sensors available
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
Campbell, 2004 ECH 2 OmV ECH 2 OmV 2500 mV excitation Converting eqs. provided by the manufacturer are for Soil only.
Problem Converting equations for soil can’t applied to other growing media such as Sphagnum moss and bark.
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
Conversion from gravimetric moisture ratio to Volumetric moisture ratio g water g media Bulk density m 3 water m 3 media
Bulk Density, g/cm 3 Orchiata Bark No. Bulk density Sp. Moss Bulk density NZ Loose Tight Chile Loose Tight China Loose Tight
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
Use it directly, do not submerge the bark in the water before use.
Difference due to pre-submerge in Tap water Orchiata bark #9Orchiata bark #5 Orchiata bark #8 w/ w/o
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
Orchiata bark #9Orchiata bark #5 Orchiata bark #8 Difference due to pre-submerge in Tap water
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
3 sources of Sphagnum Moss were investigated Imported from New Zealand (NZ) Chile China
Experiment of tightness of Sphagnum Moss filled in a pot
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
Difference due to tightness of NZ Sphagnum Moss filled into a pot Photos taken after the experiment tight loose
Difference due to tightness of Chile Sphagnum Moss filled into a pot
Difference due to tightness of China Sphagnum Moss filled into a pot
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.
sources pHEC, mS/cm NZ Chile China Tap water NZChileChina
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
ECH 2 O-10 vs. ECH 2 O-5
NZ Chile China Using ECH 2 O-10 in various EC range
Using ECH 2 O-5 in various EC range NZ Chile China
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
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
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
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
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.
Thank you for your attention
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.
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.
Dielectric constant of some materials at room temperature MaterialDielectric constant Vacuum1 (by definition) Air Teflon2 Paper3 Soil Minerals4 Rubber7 Methyl Alcohol30 Water80 Barium Titanate1200