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SC-1 Leaf Porometer

Introduction

Designed by Decagon, a leading US instrumentation manufacturer, the SC-1 Leaf Porometer automatically measures stomatal conductance and eliminates human error by picking the end point. The direct readout displays data in terms of either conductance or resistance. The data can then be saved and downloaded to your PC via an included RS232 cable and download utility software.

Features and Benefits

The Porometer embodies simplification.The automatic read mode removes the subjectivity of determining the end point and allows for fast measurement of the stomatal conductance in 30 seconds. The manual mode exists for those who want to see and record the data manually.

Benefits

Automatic sampling mode eliminates user subjectivity
Accurate Steady-State measurement
No daily calibration needed
No tubes, pumps, or fans
Simple, easy-to-use interface
"AA" battery-powered
No shoulder slings or straps
Lightweight handheld readout
Non-destructive measurement
Low cost

Features

Robust Delrin and aluminum sensor head.
Compact Clip and box make it easy to hold
Extremely lightweight 450g (under 1 lb).

3 SELECTABLE UNITS:
mmol m^-2 s^-1 (millimoles per meter squared seconds)
m^-2 s mol^-1 (meters squared seconds per mole)
s/m (seconds per meter)

Software

Leaf Porometer Utility

The Leaf Porometer comes with a software utility program to allow you to easily download data from your Porometer. With this utility you can download data, set the system clock for your porometer, and erase old data.

The Leaf Porometer Utility may periodically be updated. To find the version that you are currently using, go to the Help menu of your utility and select "About." To allow your Leaf Porometer Utility to automatically check the current version of Software, select "Check for Utility Updates" from the Help menu. Thereafter, every time you launch the program it will check Decagon's website for the most current version.

Theory of Operation

The Porometer measures the stomatal conductance of leaves using a steady state technique. The steady state technique measures the vapor pressure and vapor flux of a leaf surface. The Decagon Leaf Porometer clamps a chamber with a fixed diffusion path to the leaf surface. It measures the vapor pressure at two locations in the diffusion path, then computes flux and gradient from the vapor pressure measurements and the known conductance of the diffusion path.

Other types of Porometers

There are basically 4 methods for measuring stomatal conductance:

Mass flow (air under pressure forced through leaf)
Dynamic (rate of change of vapor pressure in cup attached to leaf) In this type, a small chamber containing a fast response humidity sensor is sealed to the leaf surface. Dry air is pumped through the chamber to achieve a pre-set humidity, then the time required for the chamber humidity to rise to some other preset value is measured.
Null balance (adjust flow of dry air to maintain cuvette vapor pressure constant) In this sytem a chamber is attached to a leaf (or a leaf is enclosed in a chamber) and the flow of dry air through the chamber is controlled such that the humidity in the chamber remains constant. The change in air flow is measured to calculate conductance.
Steady state (measure the vapor flux and gradient near a leaf).

There are a variety of ways to define "steady state". The Decagon porometer measures diffusion through a pathway. Other porometers that are "steady state" monitor the time versus the reading until nothing is changing or is steady. This method is more similar to the null balance porometer.