METER SC-1 User Manual

4
OPERATION
2.2 TAKING A MEASUREMENT
Before using the SC-1, install the batteries (Section4.2.1) and set the date and time
(Section2.1). Review factors that may affect measurements (Section2.2.1) and follow the
measurement process closely (Section2.2.2).
2.2.1 MEASUREMENT CONSIDERATIONS
Leaf stomatal conductance depends on the amount of shade and sunlight the leaf receives,
its age, and its position on the plant. To obtain a plant stomatal conductance average, take
a variety of readings from different positions on the plant. The average will be proportional
to the type of readings taken. For example, if the plant receives 70% sunlight, take seven
readings from the sunny part and three from the shady part. Do not make repeated
measurements on the same spot on a single leaf.
NOTE: Prolonged exposure (>2 min) to low RH conditions induces stomatal closure in most plant species. The
SC-1 Auto mode measures stomatal conductance in 30 s, so the presence of the desiccated leaf clip should not cause
stomatal closure unless multiple measurements are made in quick succession on the same location of the same leaf.
Average readings can also be taken for a field of plants. For example, readings from a leaf on
the same place of each stalk of corn in a field would give an average for that field.
While taking measurements or storing the sensor, avoid chemical fumes (e.g., alcohol,
gasoline, or volatile organics). Fumes can be extremely harmful to the sensor (Section4.3).
The following factors will affect measurements taken by the SC-1:
• Light: Stomatal conductance readings vary in different lights. Readings taken on overcast
days, in shadow, or in shade generally have lower conductances than those taken in
greaterlight.
• Temperature: Temperature also affects stomatal conductance readings. For most plants,
extreme temperatures (very hot or very cold) will cause photosynthesis to slow down or
stop and the stomata will narrow or close.
• Relative Humidity: RH at the leaf surface will affect readings. Stomata open more widely as
RH increases.
• Carbon Dioxide: An increase in carbon dioxide (CO
2
) causes the stomata to close, while a
decrease causes them to open. Exhaling CO
2
directly onto the plant will adversely affect
readings, particularly in growth chambers or greenhouses.
Additionally, METER recommends always using desiccant to take readings. If operators wish
to make readings without desiccant, METER recommends doing so at an ambient RH of
<30%. Follow these exceptions when measuring without desiccant:
• Remove the desiccant chamber from the sensor head and do not cover the hole in the
sensor head. Keep fingers away from the diffusion path when taking measurements.
• Recalibrate the sensor without desiccant (Section4.1).
• Allow equilibration between measurements at ambient RH by opening the clip and shaking
the sensor head to mix the air in the diffusion path.

METER SC-1 Specifications

General

Brand	METER
Model	SC-1
Category	Measuring Instruments
Language	English