Fast, Accurate Water Potential
Measurements
Use the WP4C to measure water potential in 5 to 10 minutes. Range:
-0.1 to -300 MPa*
Versatile
The WP4C can be used to measure the water potential of any porous
material. It"s typically used to analyze soil, soilless substrates, plant
material, and seeds, but it has been used to measure a variety of unusual
things, including apples, bricks, oil, and insect carapaces.
Easy Operation
Simply place the sample in a round sample cup (4cm in diameter and 1cm
tall) and set the cup in the lexan sample drawer, slide in the drawer and turn
the knob to seal the chamber. After about 5 minutes, the WP4C will beep
and show your final water potential reading.
Precise Mode
Measurements can be inaccurate if they"re made too soon. When run
in Precise Mode, the WP4C checks to make sure the sample has reached
equilibrium before displaying a final reading.
Faster Equilibration
The WP4C"s nickel Teflon sample chamber coating is hydrophobic.
Less water absorption in the sample chamber means faster equilibrium.
Finely Tuned Calibration
The WP4C sensor is durable and easy to clean. The instrument can
be calibrated using saturated salt solutions (mix your own or order
single-sample vials of standards on the accessories tab). New algorithms
let you fine-tune calibration for excellent accuracy (±0.05 MPa or better).
Plug WP4C Data into HYPROP Data Evaluation Software
The HYPROP FIT Software can be used
to plug in water potentail data collected by the WP4C for fitting different
water retention models (i.e. van Genuchten, van Genuchten Bimodal, Brooks &
Corey).
Learn More
How Does it Work?
Chilled Mirror Dewpoint Technique
The WP4C measures water potential by determining the relative humidity
of the air above a sample in a closed chamber (an AOAC-approved method; also
conforms to ASTM 6836). Once the sample comes into equilibrium with the
vapor in the WP4C"s sealed chamber, the instrument finds relative humidity
using the chilled mirror method. This method entails chilling a tiny
mirror in the chamber until dew just starts to form on it. At the
dewpoint, the WP4C measures both mirror and sample temperature with 0.001°C
accuracy. This allows the WP4C to deliver water potential readings with
unparalleled accuracy in the -0.1 MPa to -300 MPa range
Limitations
The WP4C range goes to 0 MPa, but
readings of samples wetter than -0.1 MPa will have an increasing, and typically
unacceptable, percentage of error. Some users may be able to make useful
measurements in samples wetter than -0.1 MPa using special techniques.
For more information, see the WP4C User Manual.
Limits of the Method
At high water potentials, the
temperature differences between saturated vapor pressure and the vapor pressure
inside the sample chamber become vanishingly small. Because of this, the
WP4C can now resolve temperatures to a thousandth of a degree. To read
water potentials in the wet range (0 to -0.1 MPa), we recommend German
manufacturer UMS"s fast response tensiometers and HYPROPmoisture release
curve instrument.
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ACCURACY
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±0.05 MPa* from 0 to -5 MPa
1% from -5 to -300 MPa
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RANGE
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-0.1 to -300 MPa*
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MEASUREMENT
TIME
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In precise mode:
10-15 minutes for most soil samples
20 minutes for plant tissue samples
In fast mode:
<5 minutes (reduced accuracy)
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TEMPERATURE
CONTROL
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15 to 40°C (± 0.2°C)
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SENSOR
TYPE
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1) Chilled-mirror dewpoint sensor
2) Infrared temperature sensor
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OPERATING
ENVIRONMENT
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5 to 40°C (41 to 104°F)
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WARRANTY
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1 year, parts and labor
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SAMPLE CUP
CAPACITY
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7 mL recommended (15 mL full)
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WEIGHT
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3.2 kg (5.2 kg shipping weight)
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DIMENSIONS
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24.1 x 22.9 x 8.9 cm (9.5 x 9.0 x
3.5 in)
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CASE
MATERIAL
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Powder-painted aluminum
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DATA
COMMUNICATIONS
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RS232A compatible
8-data bit ASCII code
9600 baud
no parity
1 stop bit
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POWER
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110 VAC to 220 VAC, 50/60 Hz
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DISPLAY
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20 x 2 alphanumeric dot-matrix LCD
with backlighting
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INTERFACE
CABLE
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Standard RS232 serial cable
(included)
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COMPATIBLE
STANDARDS
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ASTM D6836-07
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