The standard in water potential measurement, Wescor's Dew Point

Microvoltmeter, mode HR-33T, can determine water potential using

both dew point and wet bulb methods.  It contains sophisticated

sensing and control circuity that automatically maintains the

temperature of the thermocouple junction at the dew point mode.

The HR-33T can be used in both a laboratory and a field environ-

ment .  When coupled with our our Virtual Strip Chart Recorder

(part AC-050) the HR-33T is ideal for teaching students about

water potential determination using psychrometric principles.

The Sample Chamber measures water potential of small samples

in the laboratory or in the field without requiring a constant

temperature bath.

A precision thermocouple transducer in an internal chamber functions

either as a psychrometer (wet bulb depression method), or as a

hygrometer (dew point depresson method) depending upon the

type of readout equipment employed. Researchers have reported

exceptional ease and accuracy using this chamber, resulting in

more and better data from field and /or laboratory research. 

An all-metal thermocouple mount provides direct thermal contact

between the thermocouple and the upper heat sink. 

This and the solid aluminum housing give more rapid temperature

equilibraton and reduced zero offset error.  A copper-constantan

temperature sensor allows accurate chamber temperature measure-

ments to be made for correction of psychometric readings for

Πv temperature correction when large temperature changes are

encountered.

The proven transducer in soil research programs, Wescor's in

situ soil psychrometers, model PST-55 are buried within the

bulk soil to determine the soil water potential.  The PST-55

has a stainless steel screen  to allow only the water vapor

to enter the sensor.  A ceramic screen is also available as

model PCT-55.  To maintain temperature equilibrium, the

sensors must be buried at least 15 cm under the soil surface.

The soil psycorometer must be connected to a Wescor water

potential instruements such as the PSYPRO, HR-33T, or

CR-7 for operation.

 The L-51 Leaf Hygrometer is designed for in situ measurement

of leaf water potential, using either the wet bulb or dew point

method of data readout.  L-51A has a special chamber

configuration for use with grass.  The all-metal thermocouple

mounting system is similar to that used in the C-52 Sample

Chamber.  Given isothermal conditions, this configuration

provides rapid equilibration and excellent precision.