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Enabling better global research outcomes in soil, plant & environmental monitoring.

PSY1 for Osmotic Potential

The PSY1 psychrometer can measure the osmotic potential of plant materials such as leaves as well as stem and leaf water potential. The PSY1 for Osmotic Potential is a complete package including sensors, data loggers, insulation material, and power supply.

Osmotic potential can be performed on extracted sap samples or destructively sampled leaf tissue or leaf discs. These measurements can be made in the lab or in the field. Samples are placed in the calibration lid of the PSY1 Stem Psychrometer.

The psychrometer chamber is housed in the Osmotic Potential Insulator (OPI) to provide a thermally insulated boundary around the chamber. This eliminates the introduction of thermal gradients caused by a need to handle the chamber to load samples and provides a stable insulated thermal buffer from ambient temperature gradients within the surrounding environment.

Removing these factors enables a very rapid equilibration time between samples and high accuracy of measurement from -0.1 MPa to -10 MPa.

Osmotic potential measurements are typically performed in a manual process. Using the Graphical User Interface (GUI) the PSY1 provides the user with a manual mode to facilitate the measurement of osmotic potentials from destructive samples.

The PSY1 can also be operated in an automated logging mode and data continuously collected.
The PSY1 Stem Psychrometer is a very powerful and flexible instrument. It can measure both osmotic potential and water potential.

Performance Verification:

Independent testing by the University of New England, Armidale, Australia demonstrated that the PSY1 yields osmotic potential measurements as accurately (or more so) than the Wescor VAPRO Osmometer and within the same 40 second equilibration time per sample.


Photo 4. The PSY1 graphical User Interface performing an Osmotic potential measurement on an extracted sap sample from a wheat plant.


The difference being that the PSY1 can perform these measurements either in the lab or in the field. Never before have osmotic potentials and water potential been able to be measured in the field using the same instrumentation.



Figure 1a. All values are within ± 0.10 MPa of the expected outcome for calibration standards.



Figure 1b. Linear regressions performed on the repeated measurements data for each molal standard were all significantly correlated (P<0.01), with R-squared values of 0.99.


Application Results:

The PSY1 was subsequently used to measure the osmotic potential of both herbaceous crop plants and woody perennials.


Wheat (Triticum aestivum)


Figure 15. Comparisons for repeated measurements of osmotic potential (MPa) between
the PSY1 and Wescor Vapro 5520 for wheat (Triticum aestivum) during bench dry-down on extracted sap samples using thermal isolation unit with standardised measurement protocol.
Values are means ± s.e (n=3).


Chickpea (Cicer areitinum)



Eucalyptus michaeliana


Correlation between PSY1 & VAPRO Values are means ± s.e (n=3).


Units MPa
Range -0.1 MPa to -10 Mpa (1 to 100 Bars)
Resolution 0.01 MPa (0.1 Bar)
Accuracy ±0.1 MPa (1 Bar)
Response Time Measurement mode: 51 seconds
Live mode: 1 second
Sampling Rate 10 Hz


Computer Interface USB, Wireless RF 2.4 GHz
Data Storage MicroSD Card
Memory Capacity Up to 16GB, 4GB MicroSD card included.

Operating Conditions

Temperature Range -10 to 50°C
R/H Range 0-99%


Chamber Length: 170 mm
Width: 80 mm
Depth: 35 mm


Instrument Logging

Analogue Channels 1x Input (1x Sensor) High precision 24bit ADC Circuit.
1x Output – PSY Chamber Heater Circuit.
Resolution 0.00001V—24-Bit
Accuracy 0.001V
Minimum Logging Interval 1 second
Delayed Start Suspend Logging, Customised Intervals
Sampling Frequency 10Hz


Communications USB, Wireless Radio Frequency 2.4 GHz
Data Storage MicroSD Card, SD, SDHC & SDXC Compatible (FAT32 format)
Software Compatibility Windows Windows 8, 8.1, 10 and Mac
Data Compatibility FAT32 compatible for direct exchange of SD card with any Windows PC and Mac
Data File Format Comma Separated Values (CSV) for compatibility with all software programs
Memory Capacity Up to 16GB, 4GB MicroSD card included.

Operating Conditions

Temperature Range -40°C to +80°C
R/H Range 0-100%
Upgradable User Upgradeable firmware using USB boot strap loader function


Internal Battery Specifications
960mAh Lithium Polymer, 4.20 Volts fully charged
External Power Requirements
Bus Power 8-30 Volts DC, non-polarised, Current draw is 190mA maximum at 17 volts
USB Power 5 Volts DC
Internal Charge Rate
Bus Power 60mA – 200mA Variable internal charge rate, maximum charge rate of 200mA active when the external voltage rises above 16 Volts DC
USB Power 100mA fixed charge rate
Internal Power Management
Fully Charged Battery 4.20 Volts
Low Power Mode 3.60 Volts –  Instrument ceases to take measurements
Discharged Battery 2.90 Volts –  Instrument automatically switches off at and below this voltage when no external power connected.
Battery Life varies
  • With a recommended power source connected, operation can be continuous.
  • 3 days at hourly logging interval without chamber heating
  • 1 day with chamber heating
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