Section 3
3-4
Operation
Command Input
The
Command Input
connector is used to provide a means of controlling
the temperature setting of the LI-610 from an external device (i.e., a
computer with an analog output board). One BNC connector with
attached millivolt leads is included for connection to this device.
The
Command Input
requires a 0 to 5 volt input; the corresponding
temperature set is linear, and is equivalent to 1 °C per 100 mV. For
example, an input signal of 3250 mV would produce a dew point
temperature output of 32.50 °C. The display will show the actual
temperature set point for the
Command Input
when the selector switch is
in the “Temp Set” position, regardless of what the knob setting is.
Connect the red lead from the BNC connector to the positive terminal of
the output device, and the black lead to the signal ground. The output
device must be able to supply 1 mA drive current. A source impedance
≤
10
Ω
is required for an error
≤
0.1%.
☞
NOTE: The LI-COR LI-6400 Portable Photosynthesis System can be
configured to provide an analog output channel that controls the dew
point temperature of the LI-610. If both instruments are powered by AC
power, a "ground loop" can develop, in which there is more than one
ground connection path between the two pieces of equipment. Ground
loop-induced voltages cause unwanted signal noise that can affect the
operation of the LI-610. If you are using the LI-6400 and LI-610 in this
manner, we recommend that you isolate the two circuits by operating one
or both of the instruments with battery power.
Analog Output
The
Analog Output
connector is similar to the
Command Input
connector, in that BNC millivolt leads are used to provide an analog
signal from the LI-610 to an external recording device. Analog output is
also linear (± 5 volts), and is equivalent to 1 °C per 100 mV.
Connect the red lead to the positive terminal of the readout device, and
the black lead to the signal ground. The readout device should have an
input impedance
≥
100k
Ω
for an error
≤
0.1% (the
Analog Output
impedance is 100
Ω
).
