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 dew point Hygrometer is a fast, accurate way to measure water potential in any porous material. Typically used to analyze soil, soilless substrates, plant material and seeds, it has been used to measure a variety of unusal things, including apples, bricks 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 Dew Point 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 dew point, 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 HYPROP moisture release curve instrument.

*Note: 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.

 

ACCURACY ±0.05 MPa* from 0 to -5 MPa
1% from -5 to -300 MPa
RANGE

-0.1 to -300 MPa*

MEASUREMENT TIME

In precise mode:

10-15 minutes for most soil samples

20 minutes for plant tissue samples

In fast mode:

<5 minutes (reduced accuracy)

TEMPERATURE CONTROL 15 to 40°C (± 0.2°C)
SENSOR TYPE 1) Chilled-mirror dew point sensor
2) Infrared temperature sensor
OPERATING ENVIRONMENT 5 to 40°C (41 to 104°F)
WARRANTY 1 year, parts and labor
SAMPLE CUP CAPACITY 7 mL recommended (15 mL full)
WEIGHT

3.2 kg (5.2 kg shipping weight)

DIMENSIONS

24.1 x 22.9 x 8.9 cm (9.5 x 9.0 x 3.5 in)

CASE MATERIAL

Powder-painted aluminum 

DATA COMMUNICATIONS

RS232A compatible
8-data bit ASCII code
9600 baud
no parity
1 stop bit

POWER

110 V to 220 V AC 50/60Hz

DISPLAY

20 x 2 alphanumeric dot-matrix LCD with backlighting

INTERFACE CABLE

Standard RS232 serial cable (included)

COMPATIBLE STANDARDS

ASTM D6836-07

NOTE*

Samples wetter than -0.5 MPa will have increasing percentages of error.  Some users may be able to make useful measurements to  -0.1 MPa using techniques outlined in the user manual.

 

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Disposable Sample Cups

15 ml disposable sample cups come in lots of 500. Tight seal prevents changes in water activity as the sample is stored or comes to equilibrium.

Stainless Steel Sample Cup

Ideal for use with drying ovens. Set of 10.

Temperature Equilibration Plate

Pre-equilibrate samples to the WP4C's temperature for faster water potential measurements.

Rapidly heat or cool samples.

Small, compact size uses little bench space.

Versatile Temperature Plate can be used for other lab applications.

Travel Case

Transport and protect your valuable WP4C water potential meter in this sturdy carrying case.

Verification Standards

The WPC-4 should be regularly checked against known water activity standards. These specific-molality salt solutions in single-use disposable vials make verification quick and easy.