Auto Controls

The Auto Controls (under the Environment tab) are settings that instruct the LI-6800 to control a variable setpoint based upon parameters that you specify. The auto controls can be configured to change during a prescribed time period. Auto controls will override any setpoint or manual settings on the individual environmental control tabs.

Figure 3‑23. Any Auto Control can control any variable.

Each control can be configured to be:

  • A setpoint at the start time: F(0).
  • A setpoint at the stop time: F(x), where x is the time period in minutes.
  • The Period (minutes) with the option to repeat automatically.
  • A shape: F(t), which can be linear, step, sine/4, sine/2 (half sine), or tracking.
  • Choose the shape of the line to instruct the auto program

As an Auto Control is in progress, you can change the timing:

Jump to start with forward direction.
Jump to arbitrary time. Tap to choose a time setpoint.
Reverse direction.
Jump to end with reverse direction.

Auto Controls can be used for tracking. Rather than following a prescribed curve, such as a linear change between two end points, in tracking mode the setpoint comes from some other measurement or computation. The F(0) and F(x) values are meaningless in this mode, but the Period still matters, unless AutoRepeat is on, in which case tracking will run forever.

The following exercise shows a basic CO2 Auto Control. Begin by setting up a graph so you can see the measurements as the curve develops. Be sure the instrument has a charged CO2 cartridge and fresh soda lime.

  1. Set up a graph that shows CO2_r and CO2_s.
  2. This might be graph C by default, but if not, select a graph to configure, then:
    • Tap Edit Graphs
    • Tap + and add the variables CO2_r and CO2_s, if needed
    • Set Y-scaling to Fixed
    • Set Y-axis to Y-left
    • Set the range to Min: 100 and Max: 600 µmol mol-1.
  3. Configure the Flow controls. Under Environment > Flow:
    • Turn flow On
    • Set Pump speed to Auto
    • Set Flow to 500 µmol s‑1
  5. Close the empty leaf chamber.
  6. Configure the Auto Control. Under Environment > Auto Controls > Control: CO2_r, set the following:
    • F(0): 200 µmol mol‑1
    • F(x): 500 µmol mol‑1
    • Period: 1 minute
    • AutoRepeat: Check the box
    • F(t): Sine/2
  9. Tap the Start button to start the Auto Control.
  11. Go to the Measurements tab and watch the graph develop for a few minutes. After a few minutes go back to the Auto Control tab and set F(t): linear.

Now set some Auto Controls on fan speed, flow rate, H2O, light, and temperature to see how they work.

Keep in mind that the instrument is not logging any data. That will come later, in Open a log file.

When the instrument is running an Auto Control, the environmental controls will be covered with a box that says Controlled by Auto .... It will not prevent you from making changes, and in fact you can. When you change a setting using the manual controls, the setting will apply until the next auto control takes over. It will be hard to manually override an auto control because the settings are changing every few seconds.

Control picker

When choosing controls, either in Auto Controls or Programs, you select a Group, and from that group, a variable Name. The groups and names are available for Auto Controls and Programs. Several Programs are capable of setting constants and settings, and those groupings are shown in Table 3‑6.

Automatic chamber environment controls

Table 3‑5. Environmental controls that can be selected in the AutoEnv interface.
Group Name Description
Env Aux Controls AuxPwr Auxiliary power in head (0 to 19 V)
Dac1 DAC 1 (pin 2) -5 to +5 V
Dac2 DAC 2 (pin 3) -5 to +5 V
Dac3 DAC 3 (pin 4) -5 to +5 V
Dac4 DAC 4 (pin 5) -5 to +5 V
Env CO2 Controls CO2_% Injector control 0 to 100%
CO2_r Reference CO2
CO2_s Sample CO2
Env Fan Controls Fan_% Fan power (0 to 100%)
Fan_blc Boundary layer conductance target (mol m-2 s-1)
Fan_rpm Fan speed (rpm)
Env Flow Controls Flow_% Percent flow to chamber (0 to 100%)
Flow Flow to chamber (µmol s-1)
Env H2O Controls Desiccant_% Desiccant (only) control (0 to 100%)
H2O_% Full desiccant to full humidifier (-100 to 100%)
H2O_r Reference H2O (mmol mol-1)
H2O_s Sample H2O (mmol mol-1)
Humidifier_% Humidifier (only) control (0 to 100%)
RH_air Chamber RH (0 to 10%)
SD_air Saturation Deficit (kPa)
VPD_leaf VPD of leaf (kPa)
Env Light Controls Q_All All attached light sensors
Q_Console Console light source only
Q_Flr Fluorometer only
Q_Head Head light source only
Qin All light sources contributing to Leaf Q
Env Pressure Controls Pressure Chamber over pressure (kPa)
Pressure_% Overpressure valve (0 to 100%)
Env Temperature Controls Tair Chamber air temperature
Tleaf Leaf temperature
Txchg Heat exchanger temperature

Constants available in control loops

Table 3‑6. Environmental constants that can be changed via the MCLoop interface.
Group Name Description
Env Color Controls Color_All All attached sources
Color_Con Console light source
Color_Flr Fluorometer
Color_Head Head light source
Color_Qin All sources contributing to Leaf Q
Flr Constants FLR:Adark Dark respiration rate
FLR:Fm Maximal fluorescence
FLR:Fo Minimal fluorescence
FLR:PS2/1 Ratio PS2 to PS1
Flr Dark Settings DARK:After Far red off _ secs after actinic off
DARK:Before Far red on _ secs after actinic off
DARK:Duration Actinic off duration
DARK:FarRed target Far red target
Flr Induct Settings IND:Duration Flash duration
IND:Red target Red flash target
Flr MPF Settings MPF:Phase 1 Phase 1 duration
MPF:Phase 2 Phase 2 duration
MPF:Phase 3 Phase 3 duration
MPF:Ramp Percent ramp
MPF:Red target Red flash target
Flr RF Settings RF:Duration Flash duration
RF:Red target” Ref flash target
Gas Exchange Constants Const:Custom Custom BLC
Const:Geometry 0=broadleaf, 1=needle, 2=custom
Const:K Stomatal ratio
Const:S Leaf area (or Mass)
Leaf Temp Constants LTConst:deltaTw Wall - Air temp difference
LTConst:fT1 T1 weighting
LTConst:fT2 T2 weighting
LTConst:fTeb EB weighting
System Constants SysConst:AvgTime Average time
SysConst:Oxygen Oxygen percentage
User Defined Constants ? whatever is defined