LI-COR LI-190SA, Инструкция по эксплуатации

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7
Example:
Calculate the millivolt output of an LI-190SA Quantum
Sensor which has a calibration constant of 8.0
µ
A/1000
µ
mol s
-1
m
-2
.
Assume the 2290S millivolt adapter is used with the sensor.
8.0 A
1000 mol s m
1 A
10 A
6 Ohm =
0.004832 volts
1000 mol s m
-1 2 6 -1 2
µ
µ
×
µ
×
µ
− −
04
Or, = 4.83 mV/1000
µ
mol s
-1
m
-2
The shield of the coaxial cable on LI-COR light sensors is positive and the
center conductor is negative. (The trans-impedance amplifier used in
LI-COR light meters requires a negative signal). For data logger or
millivolt applications where the millivolt adapter is used, 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. The negative (blue) lead is connected to the signal input. This
will minimize noise.
If plus or minus capability is not available on the data logger or recorder,
the red lead should be connected to the positive input and the black lead to
the negative input. If noise difficulties are encountered, consult LI-COR for
special wiring instructions.
The BNC connector and millivolt adapter are not weatherproof. If the
millivolt adapter is attached to the sensor for connection to a data logger or
millivolt recorder, this connection should be made at the recorder end
(indoors). This eliminates thermocouple effects caused by exposing the
BNC connector and millivolt adapter to rapidly changing direct solar
radiation. These effects are not noticeable when the connectors are used
indoors out of direct radiation.
If a longer cable is needed for your application, use LI-COR extension cable
(2222SB or 2222SB-100), or coaxial (RG174) cable. Cables
≤
700 feet
(213 m) can be used if the signal is not degraded by electrical interference
from electromagnetic fields (i.e., from radio transmitters). If you need to
use a cable longer than 700 feet, use a heavier gauge coaxial cable (i.e.,
RG122). The total DC resistance of the extension cable used with the
LI-200SA must be
≤
75
Ω
. The voltage developed across the sensor's
photodiode should not exceed 20 mV . Calculate the voltage according to
[Total cable resi mV adapter resistance (
Ω
)]
×
sensor output (
µ
A) = mV.
If extension cable is used where the BNC termination will be exposed
outdoors or on a conductive surface, the BNC connection should be
insulated by wrapping it with tape. This is done to avoid ground loops.