LI-COR LI-7500, Instruction Manual

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Section 6
Troubleshooting 6-7
‘Optical Bench’ indicators:
Diagnostic Value - The cell diagnostic value is a 1 byte unsigned integer (value between 0
and 255). See Section 3, Outputs Page - Setting DAC and SDM Outputs for a description of
the integer bitmap.
PLL - Phase Lock Loop offset, indicates the status of the chopper motor. If not OK, there
may be a problem with the chopper motor in the sensor head.
Detector - If not OK, indicates the detector cooler is not maintaining the proper temperature:
this will happen at temperatures above 50 °C. Note that this does not always indicate a
serious problem; the cooler may simply have not yet reached the target temperature during
instrument startup, or it may be out of range due to external environmental conditions.
Readings may still be OK. Check cables and wiring.
Chopper - If not OK, indicates the chopper temperature controller is out of range, hot or cold.
As with the Detector indicator above, this may or may not indicate a serious problem. The
chopper should be able to temperature control when ambient is b50 and -25 °C.
Sync Flag - If not OK, indicates that the LI-7500 embedded software and the digital signal
processor (DSP) receiving the signal from the chopper motor in the sensor head are out of
sync. Check cabling.