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 substrate, 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
The WP4C is a bench-top instrument. To measure water
potential, you place the sample in a round sample cup (4cm in
diameter and 1cm tall) and set the cup in a lexan sample
drawer. You slide in the drawer and turn a 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 new WP4C checks to make sure the
sample has fully come to equilibrium before displaying a final
reading.
Faster Equilibration
The WP4C's new 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 ( order
single-sample sized vials of standards directly from Labcell
). New algorithms let you fine-tune calibration for excellent
accuracy (±0.05 MPa or better).
Plug WP4C Data into Hyprop Data Evaluation Software
They Hyprop DES 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).
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 WP4C's sealed
chamber, the instrument finds relative humidity using the chilled
mirror method. A tiny mirror in the chamber is chilled until
dew just starts to form on it. At the dewpoint, the WP4C
measures 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 will continue to measure sample water potentials to 0
MPa, but since its accuracy is ±0.05 MPa, readings above -0.05 MPa
have errors of 100% or more. -0.1 MPa is probably the the
practical limit for good accuracy. At these water potentials,
special methods should be used to maximize accuracy.
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. The WP4C can now resolve
temperatures to a thousandth of a degree. In order to read
water potentials in the "tensiometer range".
To read water potentials in the wet range (0 to -0.1 MPa), we
recommend German manufacturer UMS's fast response tensiometers and
Hyprop moisture release curve instrument.
Non UK/Ireland Customers
Non UK/Ireland Customers, please contact Decagon Devices
at: www.decagon.com
