New Measurements Mode Warning Messages

In New Measurements mode, a variety of messages can appear in the second line of the display. This section lists, in decreasing order of severity, the messages and their meanings.

These warning messages are generated by a function that runs every 10 seconds while in New Measurements mode, so they appear or disappear at 10 second intervals. (A message may linger for up to 10 seconds after the offending condition has been remedied.)

These messages can be suppressed (and re-enabled) by pressing ctrl + z (in New Measurements mode only). Also note that every time New Measurements mode is entered, the messages are re-enabled automatically.

“BLOWN FUSE (Analyzer or Flow)”

Instruments having serial number 401 and above are equipped with a back plane board that is modified to allow detection of a blown fuse. Two fuses can be detected: the analyzer board fuse, and the flow board fuse. It cannot tell which one is blown, just that one or both are blown. See Replacing the Fuses.

“IRGAs Not Ready”

See “IRGAs Not Ready” Message.

“High Humidity Alert”

The lowest value T of the three temperatures measured in or near the chamber (analyzer block, chamber air, and leaf) is used to compute a relative humidity RHalert:


where Ws is sample water concentration (mmol mol-1), P is ambient pressure (kPa), and the function es() computes saturation vapor pressure (kPa) as a function of temperature (C) (Equation 14-24 in the instruction manual). If RHalert exceeds 95%, the “High Humidity Alert” message appears. The usual remedy is some combination of the following:

  • Give the coolers a warmer target.
  • Perhaps you’re asking for a block or leaf temperature that is too cold.
  • Increase the flow rate.
  • This will reduce the chamber humidity.
  • Dry the incoming air further
  • Increase the desiccant scrubbing.
  • Water IRGA OK?
  • The problem could be with the water IRGA. Do its readings, H2OR and H2OS, make any sense? Are they responsive? (If the readings don’t seem to change, then the analyzer board fuse may be blown (Replacing the Fuses); this can happen without causing the IRGAs Not Ready message.)

“Chamber Fan is Off”

This message refers to the internal fan in the sample cell, which is controlled via function key f1 (level 2), labeled FAN. Note that the instrument cannot sense if the fan is actually moving or not; the message is what is should be doing. The only way to tell if the fan is functioning is to turn it on and off and listen for sound changes.

“Pump is Off”

If the pump is off (accomplished by selecting “None” in the Flow Control Options (2 f2 N)), this message will appear. The software senses the pump’s status by checking the digital output that controls it. If the pump is in fact not operating due to other reasons (not being plugged in, blown fuse, etc.), it will not cause this message to appear.

“Flow is Too Low”

The minimum recommended flow is 50 μmol s-1 with a 6400-01 Mixer, or 100 without. In fixed flow mode, if the flow drops below this value, the “Flow is Too Low” message will appear. Note that if OPEN is in any other flow control mode, flow rates less than this are tolerated (since the system is controlling flow rates, and not the user), and this message will not appear. If “Flow is Too Low” appears even though the requested flow rate is higher than 50 μmol s-1, check for a blown flow board fuse; the real flow may be 0 because the pump is not running. If the flow board fuse has failed, a number of other things will not be functioning as well, such as the console cooling fan, light source, light source fan, cooling fans, chamber fan, and CO2 injector.

“FLOW: Need ↑SCRUB or wetter target”

The “↑SCRUB” refers to the desiccant tube adjustment label, and the direction you should to turn the knob. Specifically, this message means that the target humidity is low, and that the flow rate can’t be increased any more in an effort to drive the humidity down. The remedies include:

  • Turn the desiccant tube knob toward SCRUB
  • If possible, drier incoming air is needed.
  • Pick a higher target humidity, (smaller VPD)
  • Reduce the leaf area
  • If the humidity is in fact dropping, wait

A variation of this message is

“FLOW: Need ↑SCRUB - H2OR > Target”

This means the reference water IRGA (and hence the air incoming to the chamber) is already higher than what you’ve asked for the target to be. Unless you can convince the leaf to remove water vapor from the air, your only recourse is to dry the air a bit, or raise the target humidity (which means reduce the VPD target, if that’s what you are targeting).

“FLOW: Need ↓SCRUB or drier target”

The water target is high enough to cause the flow to drop to its minimum, perhaps temporarily, while the system waits for the leaf to humidify the chamber. The remedies:

  • Turn the desiccant tube knob toward BYPASS.
  • More moist incoming air is needed. (See Humidifying Incoming Air).
  • Pick a lower target humidity, or larger VPD
  • Increase the leaf area.
  • Wait for the humidity to climb.

“Negative PAR! LightSource? Cal?”

The ParIn_μm reading is less than -10 μmol m-2 s-1. You likely have the wrong light source specified, since Red/Blue LED sources generate negative signals, while the Red only, and the standard chamber top light sensors generate positive signals.

“No Light Signal - Check Source”

This message will appear when the following conditions are all true: 1) Configured for LED or LCF light source, 2) D/A driving the LEDs is > 1000 mV, 3) measured internal PAR sensor signal is < 20 mV.

There are a variety of ways to get this to happen. Some represent hardware failures, and some human failures.

  • Light Source not plugged in
  • This can be either the lamp itself or the detector connector.
  • LED Source Mix-up
  • You can not treat the 6400-02 LED Source like a 6400-40 LCF, or vice versa. They get their light sensor signals from different places.
  • Lamp Failure
  • See Source Won’t Turn On (Source Won’t Turn On)

“IRGAs Warming Up”

If the IRGAs are indicating an unready state within the first 2 or 3 minutes of power on, the displayed message with be this warm-up message. After that time, the dreaded “IRGAs Not Ready”, discussed above, will appear.

“RGB Source: WARM / HOT / 5V / LowBatt / NoBatt”

This is a 6400-18 RGB Light Source warning message. See Warning Message.