LI-COR LI-192 User manual

Underwater
Quantum Sensors
Instruction Manual
LI-192 Underwater Quantum Sensor
LI-193 Spherical Quantum Sensor

Underwater Quantum Sensors
Instruction Manual
LI-COR Biosciences
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Lincoln, Nebraska 68504
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Germany
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LI-COR Biosciences UK Ltd.
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Cambridge
CB4 0WS
United Kingdom
Phone: [phone]
[email protected]
LI-COR Distributor Network:
www.licor.com/envdistributors

NOTICE
The information contained in this document is subject to change without notice.
LI-COR® MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT
LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. LI-COR shall not be liable for errors contained herein or for incidental or consequential damages in con-
nection with the furnishing, performance, or use of this material.
This document contains proprietary information which is protected by copyright. All rights are reserved. No part of this
document may be may be reproduced or translated into another language with prior written consent of LI-COR, Inc.
All other trademarks or registered trademarks are property of their respective owners.
Copyright © 2006 - 2021, LI-COR, Inc. All rights reservee.
Publication Number: 984-08307
Created on Monday, November 8, 2021
CE Marking:
This product is a CE-marked product. For conformity information, contact LI-COR Support at [email protected]. Out-
side of the U.S., contact your local sales office or distributor.
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device
may not cause harmful interference, and (2) this device must accept any interference received, including interference that
may cause undesired operation.
Printing History
New editions of this manual will include all updates. An update addendum may be used between editions to provide up-
to-date information. Revisions are indicated by the revision number. Minor updates, which do not alter the meaning of
the content, will be incorporated without affecting the revision number.
ii

iii
Contents
Section 1. General information
Sensor recalibration 1-2
Getting started 1-2
Relationship between the Calibration Constant and Calibration Multiplier 1-2
Connecting to metering devices from other manufacturers 1-3
Using the 2009S Lowering Frame 1-4
Section 2. Factory calibration procedures
Section 3. Using the quantum sensors
LI-192 Underwater Quantum Sensor 3-1
Immersion effect 3-2
Cosine response 3-2
Cosine correction properties 3-3
Spectral response 3-4
LI-193 Spherical Quantum Sensor 3-5
Immersion effect 3-5
Angular response 3-6
Azimuth response 3-6
Spectral response 3-6
Errors 3-7
Mathematical definitions 3-7
Section 4. Cleaning and maintenance
Section 5. Accessories
2222UWB Underwater Cable 5-1
2009S Lowering Frame 5-1
100L Lubricant 5-1
Millivolt Adapters 5-2
2291 Millivolt Adapter 5-2

Section 6. Bibliography
Appendix A. Specifications
Appendix B. Warranty
iv

Section 1.
General information
The LI-192SA and LI-193SA underwater quantum sensors have a coaxial cable that
terminates with a BNC connector. The 2222UWB Underwater Cables used with
LI-COR underwater sensors are terminated with this type of connector, which
allows for direct connection to the LI-250A Light Meter or the LI-1500 Light Sensor
Logger. Figure 1-1 below shows an LI-193SA sensor with the coaxial connector.
This connector also allows the sensor to be used with older (discontinued) instru-
ments, including the LI-189 Quantum/Radiometer/Photometer, LI-250 Light Meter,
the two current channels of the LI-1000 Datalogger, or with older LI-COR integ-
rators.
Figure 1-1. "SA" type sensors are terminated with only a BNC connector on the end of the
coaxial cable.
When a LI-COR Light Meter or data logger is not used, type SA sensors can be used
with other millivolt recorders or data loggers by connecting a millivolt output con-
version adapter. See Accessories on page5-1 for more information. Note that all
LI-COR underwater sensors produce a current signal, not voltage.
1-1LI-192 and LI-193 Quantum Sensors

Section 1. General information
Sensor recalibration
Factory recalibration of LI-COR radiation sensors is recommended every two years.
Sensors can be returned to LI-COR for this service – please contact our technical sup-
port staff for more information.
Getting started
All LI-COR radiation sensors produce a current proportional to the radiation intens-
ity. During factory calibration, sensor output (in microamps) is measured while the
sensor is exposed to a standard lamp of known intensity. The sensor output at this
intensity has general units of microamps per radiation unit and is called the Cal-
ibration Constant (Calconstant). Each sensor has a slightly different output at a
given radiation intensity and will therefore have a unique Calconstant.
Relationship between the Calibration Constant and Calibration
Multiplier
LI-COR Light Meters and dataloggers measure the current output of the sensor in
units of microamps, and convert the measured current to units of radiation. To
make this conversion, LI-COR instruments use the sensor Calibration Multiplier. The
Calibration Multiplier is the negative reciprocal of the Calconstant.
1-1
The LI-192 and LI-193 calibration certificates contain calibration multipliers for both
in air and in water operation. The in water multiplier includes an immersion effect
correction.
To use a type SA sensor with the LI-250, the calibration multiplier is entered in con-
figuration mode, using the up and down arrow keys to scroll the multiplier value(s).
When using the LI-1400 DataLogger, the calibration multiplier must be entered into
the software as described in the Instruction Manual.
When a LI-COR light meter or data logger is not used, your sensor can be used with
other millivolt recorders or data loggers by connecting a millivolt adapter. The LI-
192SA and LI-193SA underwater sensors require the 2291 Millivolt Adapter, which
has a resistance of 1210 Ohms.
1-2 LI-192 and LI-193 Quantum Sensors

The millivolt adapter connects to the BNC connector of the sensor, and the wire
leads of the adapter are connected to the data logger. Sensor output (in millivolts)
when using the millivolt adapter can be computed using "Ohm's Law" (Voltage =
Current × Resistance).
Example: Calculate the millivolt output of an LI-192 Underwater Quantum Sensor
which has a calibration constant of 8.0 μA/1000 μmol s-1 m-2. Assume the 2290 mil-
livolt adapter is used with the sensor.
1-2
The multiplier to use in your data acquisition system is the reciprocal of this result.
For example,
1-3
If the calibration constant for your sensor has been lost or misplaced, it can be
obtained from LI-COR by providing the serial number of the sensor.
Important: When using the sensor under water, the "in water" calibration con-
stant should be used to calculate the millivolt output of the sensor. The "in water"
sensor calibration includes an immersion effect correction.
Connecting to metering devices from other manufacturers
The use of the millivolt adapter with a recorder or data logger other than LI-COR
instruments is often acceptable for radiation levels down to 10% of full sunlight.
Below 10%, the recorder must be very sensitive to pick up the small voltage signal.
The recorder should have a high impedance input (>1 megaohm, such as poten-
tiometric types), and the range adjustment should be 0 - 10 mV, or a more sensitive
range. For low light levels, the sensor should be connected directly to a LI-COR
readout device (without using the millivolt adapter).
In LI-COR underwater cables the inner white wire is positive and the black wire is
negative. The center pin of the BNC connector has a negative signal. This is done
because the trans-impedance amplifier used in LI-COR light meters requires a neg-
ative signal.
Section 1. General information
1-3Connecting to metering devices from other manufacturers

Section 1. General information
For data logger or millivolt applications where the millivolt adapter is needed, the
positive (green) lead should be connected to the low impedance (common terminal)
when plus or minus signal capability is available on the data logger or recorder. This
will minimize noise.
If plus or minus capability is not available on the data logger or recorder, the green
lead should be connected to the positive input and the blue lead to the negative
input. If noise difficulties are encountered, consult LI-COR for special wiring instruc-
tions.
Using the 2009S Lowering Frame
It is recommended that the LI-COR 2009S Lowering Frame (or equivalent) be used
with the sensor for underwater applications.
Important: Do not use LI-COR 2222UWB Underwater Cable to support the
sensor and lowering frame, as damage to the cable can result. An auxiliary cable
should be used to support the lowering frame and sensor. In addition, the
2222UWB cable should not be bent sharply near the sensor.
Note: For cable lengths over 75 m (225 ft.), care should be exercised in its use
since movement of the cable within the water can cause excessive signal noise.
The 2009S Lowering Frame provides for the placement of two cosine sensors, one
each for upwelling and downwelling radiation, or a single underwater spherical
sensor (Figure 1-2 on the facing page). Each LI-COR underwater sensor has three 6-
32 tapped mounting holes on the underside of the sensor for connection to the
mounting ring. Corrosion resistant mounting screws are included with each sensor.
A replacement screw and insulating washer kit is available from LI-COR (p/n 9901-
220).
1-4 LI-192 and LI-193 Quantum Sensors

Figure 1-2. 2009S Lowering Frame.
When two sensors are used, the frame is well balanced and will work well in mild
currents without twisting the cables. The sensor for downwelling radiation is always
attached using the mounting ring on the fin. Likewise, the sensor for upwelling radi-
ation is attached to the opposite mounting ring. Depending on the speed of the cur-
rent, the frame will tilt a few degrees, but this can be minimized by hanging a
compact weight from the weight ring. Moderate weights will often suffice (4 kg).
Weights over 25 kg should be avoided.
The use of a single cosine sensor will require a small weight (0.2 kg) attached at the
empty mounting ring or a moderate weight from the weight ring, or possibly both,
depending upon the speed of the current. The underwater cable(s) should be
attached to the frame such that approximately 25 cm of cable forms a smooth arc to
the underwater sensor connector and is restrained from being flexed or supporting
any weight.
The LI-COR underwater cable is not recommended as a support cable, although it
can be used as a lowering cable providing it is properly attached and the attached
weights do not exceed 5 kg. The cable(s) must be attached as described above. Addi-
tionally, the cable must be securely attached to the shaft of the lowering frame at
multiple points so that the cable does not slip and put strain on the sensor con-
nector. However, the cable cannot be clamped so tightly as to damage it. Possible
methods to use are numerous nylon cable clamps along the length of the shaft, or a
tight wrap of light cord around the shaft and cables, starting at the suspension ring
and extending downward at least 25 cm.
Section 1. General information
1-5Using the 2009S Lowering Frame

Section 1. General information
Figure 1-3. Attach the cable to the lowering frame at several points.
1-6 LI-192 and LI-193 Quantum Sensors

Figure 1-4. Attach a small weight to the lowering frame when using a single sensor.
For long-term immersion or use in heavily ionic water, it may be necessary to
provide electrical insulation between the underwater sensor(s) and the lowering
frame to prevent galvanic corrosion. This is accomplished by slipping an insulating
flat washer over the mounting screws down to the heads, followed by a 1/2" (13
mm) length of thin tubing over the screw threads. This tubing insulates the screws
from the mounting ring.
Next, place a large flat insulating washer between the sensor and the mounting ring
(with three holes for the screws). Use the "insulated" screws to attach the sensor in
place. In this way, neither the screws nor sensor have electrical contact with the
frame.
Section 1. General information
1-7Using the 2009S Lowering Frame

Section 1. General information
Figure 1-5. Use an insulating washer in heavily ionic water.
1-8 LI-192 and LI-193 Quantum Sensors

Section 2.
Factory calibration procedures
LI-COR quantum sensors are calibrated using a standard light source calibrated
against a National Institute of Standards and Technology (NIST) lamp. The photon
flux density from the standardized lamp is known in terms of micromoles s-1 m-2
where one micromole = 6.022 × 1017 photons.
The uncertainty of the calibration is ± 5%. The lamp used in LI-COR's calibration is
a high intensity standard of spectral irradiance (G.E. 1000 watt type DXW quartz
halogen) supplied with a spectral irradiance table.
The following procedure is used to calculate the quantum flux output from the
lamp. The lamp flux density (E) in watts m-2, in an increment at a wavelength can
be expressed as
2-1ΔE=E(λ)Δλ
where E(λ) is the spectral irradiance of the lamp at wavelength λ.
The number of photons s-1 m-2 in Δλis
2-2
where his Plank's constant and cis the velocity of light. This can be summed over
the interval of 400-700 nanometers (nm) to give
2-3
The result is adjusted to μmol s-1 m-2 by dividing by 6.022 × 1017.
2-1LI-192 and LI-193 Quantum Sensors

Section 2. Factory calibration procedures
2-2 LI-192 and LI-193 Quantum Sensors

Section 3.
Using the quantum sensors
The procedures for using the LI-192 and LI-193 are very similar.
LI-192 Underwater Quantum Sensor
The LI-192 Underwater Quantum Sensor is used for measuring Photosynthetically
Active Radiation (PAR) in aquatic environments. With its 400-700 nanometer (nm)
quantum response, it is a valuable tool for researching primary productivity or other
projects of environmental concern. The sensor can be used in the air with accuracy
similar to that of the LI-190 Quantum Sensor. Prior to obtaining atmospheric read-
ings, the sensor must be dried.
New sensor cables from LI-COR are pre-lubricated with a thin film of silicone grease
at the factory. The sensor connector may need to be lubricated periodically with a sil-
icone grease (e.g. Dow Corning 111, available from LI-COR under p/n 210-01958-1)
before installing it in the mating connector of the underwater cable. The yellow dot
on the sensor connector should be aligned with the raised nub on the sensor cable
before pushing them together in order to obtain the proper pin connection. If the
3-1LI-192 and LI-193 Quantum Sensors

Section 3. Using the quantum sensors
dots are not aligned, this can result in a negative reading on the readout device due
to the change in polarity of the conductors.
Important: Make sure that the underwater cable is inserted fully over the “rib” of
the sensor connector before tightening the white collar on the end of the under-
water cable. If the cable is not inserted far enough, the sensor leads can be dam-
aged when the collar is threaded over the sensor connector. In addition, the
connector pins are small and care should be taken when mating the connectors.
The quantum sensor has three 6-32 tapped holes on the underside of the sensor
which are used for mounting the sensor to the 2009S Lowering Frame.
To maintain appropriate cosine correction the vertical edge of the diffuser must be
kept clean. Periodically inspect the sensor for foreign deposits on the upper surfaces
during prolonged submerged operation.
Immersion effect
A sensor with a diffuser for cosine correction will have an immersion effect when
immersed in water. The radiation entering the diffuser scatters in all directions
within the diffuser with more of the radiation lost through the water-diffuser inter-
face than in the case where the sensor is in air. This results because the air-diffuser
interface offers a greater ratio of the indexes of refraction than the water-diffuser
interface. Thus, a greater percentage of radiation entering the diffuser in air reaches
the photodiode than in the case where the LI-192 is in water. Therefore, a normal
underwater reading would need to be multiplied by this effect if the sensor is used
in water.
The LI-192 calibration certificate contains calibration multipliers for both in air and
in water operation. The in water multiplier includes the immersion effect correction.
Cosine response
Measurements intended to approximate radiation impinging upon a flat surface (not
necessarily level) from all angles of a hemisphere are most accurately obtained with a
cosine corrected sensor.
A sensor with a cosine response (follows Lambert's cosine law) allows measurement
of flux densities through a plane surface. This allows the sensor to measure flux dens-
ities per unit area (m2). A sensor without an accurate cosine correction can give a
3-2 LI-192 and LI-193 Quantum Sensors

severe error under diffuse radiation conditions within a plant canopy, at low solar
elevation angles, under fluorescent lighting, etc.
The cosine relationship can be thought of in terms of radiant flux lines impinging
upon a surface normal to the source (Figure 3-1 below) and at an angle of 60° from
normal (B in Figure 3-1 below). A in Figure 3-1 below shows 6 rays striking the unit
area, but at a 60° angle, only 3 rays strike the same unit area (B in Figure 3-1 below).
This is illustrated mathematically as:
S= (I) (cosine 60°) per unit area
3 = (6) (0.5) per unit area
where S= vertical component of solar radiation; I= solar radiation impinging per-
pendicular to a surface and cosine 60° = 0.5.
Unit
Area
A. B.
Figure 3-1. Lambert's cosine law.
Cosine correction properties
A comparison of the underwater sensor's cosine response curve in air and in water
can be found in the "Immersion Effect and Cosine Collecting Properties of LI-COR
Underwater Sensors" Report (Application Note #110, available from LI-COR). Engin-
eering requirements result in different correction characteristics for air and water.
Over-compensation occurs in air and under-compensation occurs in water. The bet-
ter response was selected for air, because in water, the direct incident solar radiation
does not exceed the critical angle of 48.6° (a result of the air-water interface).
Section 3. Using the quantum sensors
3-3Cosine correction properties

Section 3. Using the quantum sensors
Spectral response
The spectral response is similar to that of the LI-190 Quantum Sensor (Figure 3-2
below).
100
80
60
40
20
0400 500 600 700
ULTRAVIOLET VIOLET BLUE
GREEN YELLOW RED INFRARED
PERCENT RELATIVE RESPONSE
WAVELENGTH – NANOMETERS
LI-COR
QUANTUM SENSOR
IDEAL QUANTUM RESPONSE
PERCENT RELATIVE PHOTON RESPONSE
Figure 3-2. Typical spectral response of an original LI-190 Quantum Sensor vs. Wavelength
and the Ideal Quantum Response (equal response to all photons in the 400-700 nm wave-
band).
The spectral response of the quantum sensor is obtained by use of a light source and
a monochromator. A sensor which has a known spectral response over the spectral
range of interest is used to determine the monochromator output in energy flux
density, W(λ), at the wavelength setting . If Q(λ) is the sensor output at wavelength
when exposed to the monochromator output, W(λ), then Q(λ) can be approximated
by
3-1Q(λ) = R(λ)W(λ)
where R(λ) is the sensor spectral response at the wavelength setting λ. The above
approximation assumes that the monochromator bandwidth, λ, is much less than the
wavelength setting λ. The normalized sensor spectral response r(λ), is determined by
3-2r(λ) = R(λ)/Rm
where Rm is the maximum value of Q(λ)/W(λ) over the range of wavelengths meas-
ured.
3-4 LI-192 and LI-193 Quantum Sensors