RESEARCH: SENSOR EVALUATION |
|
|
CLICK ON THESE TITLES TO JUMP TO
THE ABSTRACTS BELOW:
|
 |
|
-
Cooling with
Water: An Economical Alternative for
Refurbishing Plant Growth
Chambers with Damaged Compressors
Alec Hay and Bruce Bugbee - June 2006
|
INTRODUCTION Plant growth
chambers provide a powerful tool for plant research. Tight control
over a range of environmental factors such as temperature,
photoperiod, light level, humidity, and gas enrichment make the
proper care or precision stress of plants easier to manage. This
level of environmental control comes at a high price.
While plant
growth chambers are expensive as a whole, the most expensive
component of a growth chamber is the cooling system. When the
compressor fails, replacement can cost $2,000 to $3,000 depending on
the size and model. The age of a growth chamber or the availability
of funding may make replacement of the compressor impractical. Such
a growth chamber is the ideal candidate for conversion to water
cooling. While the chamber will not be capable of cooling to near
freezing temperatures, a fully functional chamber can be up and
running for a few hundred dollars, and it will serve fully 90% of
experiments commonly done in growth chambers. |
|
|
|
INTRODUCTION
Handheld chlorophyll meters are an easy way to non-destructively
estimate chlorophyll content of leaves. The chlorophyll meters in this
study both measure ratios of radiation transmitted through the leaf at
two wavelengths. The SPAD measures the RVI (Ratio Vegetative Index) at
940 nm and 650 nm while the CCM-200 uses 940 nm and 660 nm. The
leaf area measured by each handheld meter also differs. The SPAD 502
measures a 0.06 cm2 area while the CCM-200 a 0.71 cm2
area.
|
|
|
|
INTRODUCTION The Apogee spectroradiometer package
includes a cosine corrected head. The white diffusion disc of the head
is threaded to allow adjustment of the height of the filter. The
height of the disc affects the amount of light that reaches the sensor
cable, which affects irradiance measurements.
|
|
-
Operating
Instructions for an Electronic Tensiometer:
Irrometer Models R-RSU & MLT-RSU
Derek Pinnock (Updated in 2005 by Julie Chard)
|
INTRODUCTION Tensiometers measure soil moisture based on
soil water tension. They consist of a sealed, water-filled tube with a
porous ceramic cup at the bottom and a pressure gauge at the top. The
ceramic cup is installed in the root zone of the soil profile. Changes
in soil moisture cause water to move in and out of the ceramic cup,
creating a tension in the water-filled tube. The tension is measured
by the pressure gauge.
Model “-RSU” (Remote Sensing Unit) tensiometers use an electronic
pressure transducer instead of the usual analog pressure gauge to
measure the water potential of the media. Connecting the transducer to
a datalogger makes it possible to irrigate at a selected tension
rather than a fixed time period, resulting in higher irrigation
efficiency.
Irrometer R-RSU tensiometers have fine porous cups with bubbling
pressures of 100 kPa. These are adequate for fine-textured mineral
soils but have inadequate response time to control irrigation in
soil-less media and coarse sands. Coarse textured growing media are
depleted of plant available water at relatively low tensions (8 to 20
kPa). The Irrometer MLT-RSU (Miniature Low Tension-RSU) uses a porous
cup with a bubbling pressure of 50 kPa. The lower bubbling pressure
makes it better suited for typical greenhouse growing media because it
has a faster response.
The Crop Physiology Laboratory owns three three 12-inch R-RSU and
three 6-inch MLT-RSU tensiometers. The range of each is inscribed on
the back or top of the transducer.
|
|
|
|
INTRODUCTION Barometric pressure (or atmospheric
pressure) is the force exerted on the ground surface by the
atmosphere. Barometric pressure is expressed in many different units:
1 atmosphere = 14.7 lb/in2
= 760 mm Hg = 760 torr = 1.013 bars = 101.3 kPa
The SI unit of pressure is the Pascal (Pa) and barometric pressure is best
expressed in kilopascals (kPa). The standard barometric pressure
(101.3 kPa) is the pressure at sea level at 15°C and 45° latitude.
Barometric pressure decreases with increasing elevation. To compare
pressure conditions among locations, meteorologists correct pressure
to its sea-level equivalent (Eq. 1),
dP = 1013.25{1-[1-(E/44307.69231)]5.25328} (1)
where
dP is the reduction in pressure (in millibars) resulting from
the site elevation and E is meters above sea level.
The first measurements of
barometric pressure were made centuries ago using a mercury manometer,
and even now mercury barometers are a standard reference instrument
due to their inherent accuracy. Liquid manometers, however, have
three disadvantages: 1) they are delicate and require perfectly
vertical and level mounting,
2) their readings must be manually temperature-corrected, and 3) they
do not have an electronic output.
Electronic barometric
pressure transducers can be interfaced with a datalogging system for
continuous measurement and recording. Better quality transducers are
fully temperature compensated. We tested four electronic barometric
pressure transducers in our laboratory (Table 1). Two of the sensors
are available either directly from the manufacturer or from Campbell
Scientific (model numbers in parentheses).
|
|
|
|
INTRODUCTION
The Watermark (Irrometer Company, Riverside, CA) is a granular matrix
sensor, similar to a gypsum block. It consists of two concentric
electrodes embedded in a reference matrix material, which is
surrounded by a synthetic membrane for protection against
deterioration. A stainless steel mesh and rubber outer jacket make
the sensor more durable than a gypsum block. Movement of water
between the soil and the sensor results in changes in electrical
resistance between the electrodes in the sensor. The electrical
resistance can then be converted to soil water potential.
Watermark sensors are inexpensive (about $24 each) and can measure
soil water potential over a wider range (0 to -2 bars or 0 to -200 kPa)
than tensiometers. Watermarks are compact, easily installed, and low
maintenance.
|
|
-
A Simple
Test to Evaluate the Calibration Stability
and Accuracy of
Infrared Thermocouple Sensors
Derek Pinnock and B. Bugbee
|
INTRODUCTION
Accurately measuring surface temperature is not difficult when the
surface, the sensor, and air temperature are similar, but it is
challenging when the surface temperature is significantly different
than air and sensor temperatures.
We tested three Infrared Thermocouple sensors (IRT's) that had been
used for two years in a greenhouse environment. The importance
of the correction for sensor body temperature was also examined. |
|
-
Two new techniques and 3 new instruments
for real-time measurement of
plant growth
Bruce Bugbee
- 2004
Presented at
NCR-101 conference; Brisbane, Australia
|
|
-
Selecting
among thermocouple wire types
Bruce Bugbee - 2001
Presented at
NCR-101/CUEG conference; Norwich, England
|
