Transcript Moisture Content Measurement of Bark and Sphagnum Moss Using ECH2O Sensor for the Production of Phalaenopsis Wei Fang and Walter Ray Dept.

Moisture Content Measurement of
Bark and Sphagnum Moss Using ECH2O
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
ECH2O Soil Moisture Probes
 Probe Type
 Dielectric constant measurement
 Measurement Time
 10 ms
 Resolution
 0.002 m3/m3 (0.1%)
 Power
 Requirements: 2.0 VDC @ 2mA to 5 VDC
@7mA
 Output: 10-40% of excitation voltage (250-1000
mV @ 2500 mV excitation)

Manufacturer:
 Decagon Devices, Inc., USA
-5
-10
-20
Converting eqs. provided by the
manufacturer are for Soil only.
q = 0.000695 mV - 0.29.......... ......(ECH2O- 20 )
q = 0.000936 mV - 0.376.......... ....(ECH2O- 10 )
@ 2500 mV excitation
Campbell, 2004
7 soil types tested
Soil type
Sand, ％
Silt, ％
Clay, ％
EC（mmho cm-1）
Loamy Sand
87
3
10
0.04
Sandy Loam
79
9
12
0.34
Loam
47
29
24
0.09
Silt Loam-A
*
*
*
0.2
Silt Loam-B
3
71
26
0.12
Silty Clay Loam
3
68
29
0.09
Silty Clay
17
41
42
1.48
Campbell, 2004
Problem
Converting equations
for soil can’t applied to
other growing media
such as Sphagnum
moss and bark.
Indoor Experimental setup
HID Lamp
continuously
on
g/g
Simulated
greenhouse
雙層塑膠布屋頂
雙層塑膠布屋頂
PE roof
RI 1203
inlet
Growth media
w/ sensor (no
plants)
fan
●
Loadcell
●
PC
mV
Data logger
Conversion from
gravimetric moisture ratio to
Volumetric moisture ratio
g water
g media
Bulk density
m3 water
3
m
media
Bulk Density, g/cm3
Orchiata
Bark No.
5
8
9
Bulk density
0.2656
0.28499
0.33752
Sp. Moss
NZ
Bulk density
Loose
0.1434
Tight
0.2879
Loose
0.1362
Tight
0.3024
Loose
0.1368
Tight
0.2481
Chile
China
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
w/
Orchiata bark #5
Orchiata bark #9
Orchiata bark #8
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
Difference due to pre-submerge in Tap water
Orchiata bark #5
Orchiata bark #9
Orchiata bark #8
Converting equations derived for ECH2O-10
Bark no.
Eqs.
R2
db
y = 0.0094x - 2.5492
0.8941
wb
y = 0.0049x - 1.3258
0.8715
db
y = 0.0075x - 2.0518
0.8906
wb
y = 0.0032x - 0.8758
0.8792
db
y = 0.0086x - 2.4096
0.9580
wb
y = 0.0044x - 1.2168
0.9565
5
8
9
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
tight
loose
Photos taken after the experiment
Difference due to tightness of Chile Sphagnum Moss
filled into a pot
Difference due to tightness of China Sphagnum Moss
filled into a pot
Difference due to sources of loosely filled Sphagnum Moss
China
Sp. Moss from Chile
has the greatest
water holding
capability when
loosely filled.
Sp. Moss from
When loosely filled,
China has the
3 types of moss
greatest mV output
performed quite
due to high EC of
differently.
dissolved water.
Chile
NZ
Chile
sources
pH
EC, mS/cm
NZ
4.665+ 0.07
0.203+ 0.01
Chile
4.65+ 0.03
0.143+ 0.02
China
4.743+ 0.07
0.498+ 0.02
Tap water
7.2+ 0.03
0.06+ 0.01
China
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
ECH2O-10
vs.
ECH2O-5
Using ECH2O-10 in various EC range
Chile
NZ
China
Using ECH2O-5 in various EC range
Chile
NZ
China
Small conclusion
 ECH2O-5 sensor is
less sensitive to
EC variation, that make it a better sensor
compare with ECH2O-10
Converting equations for
ECH2O-10 on Sphagnum Moss
Sphagnum Moss
db
NZ
wb
db
Chile
wb
db
China
wb
Note: y in g/g, x in mV
Eqs.
y = 0.024x - 6.4422
y = 0.0022x - 0.6037
y = 0.0248x - 6.4717
y = 0.0023x - 0.5934
y = 0.018x - 4.2573
y = 0.0016x - 0.3546
R2
0.9292
0.9421
0.9618
0.967
0.8037
0.7025
Linear equations for ECH2O-5
on Sphagnum Moss
Sphagnum Moss
NZ
Chile
China
Eqs.
R2
db
wb
y = 0.0299x - 6.2301
y = 0.0025x - 0.5243
0.9331
0.9351
db
wb
db
y = 0.0257x - 5.7949
y = 0.0023x - 0.5212
y = 0.024x - 4.6515
0.9083
0.9084
0.9312
wb
y = 0.0023x - 0.4458
0.9308
Note: y in g/g, x in mV
Polynomial equations for ECH2O-5
on Sphagnum Moss
Sphagnum Moss
Eqs.
R2
db
y = 1E-04x2 - 0.0368x + 4.8699
0.9902
wb
y = 8E-06x2 - 0.0032x + 0.431
0.995
db
y = 8E-05x2 - 0.0303x + 3.6158
0.9804
wb
y = 7E-06x2 - 0.0027x + 0.3136
0.9786
db
y = 7E-05x2 - 0.0191x + 1.841
0.9797
wb
y = 6E-06x2 - 0.0018x + 0.1797
0.9798
NZ
Chile
China
Note: y in g/g, x in mV
Conclusions
 ECH2O-10 and ECH2O-5 can be used to
continuously monitor the water content of
media used in growing Phalaenopsis.
(ECH2O-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 εr is defined as the ratio:
εr= εs / εo = εs / ( 8.85 x 10-12 F/m) = εs x 1.13 x 1011
 Where
εs : the static permittivity of the material in question,
ε0 : 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 εs is just ε0,
so the dielectric constant is unity.
Dielectric constant of some materials at room temperature
Material
Vacuum
Air
Teflon
Paper
Soil Minerals
Rubber
Methyl Alcohol
Water
Barium Titanate
Dielectric constant
1 (by definition)
1.0005
2
3
4
7
30
80
1200