Teledyne 9060L - Zirconium oxide flue gas oxygen analyzer - Manual (Page 39)

Percent Oxygen Analyzer Operation
Teledyne Analytical Instruments 39
output of the sensor higher than the top scale of the ADC. It may
also occur if the thermocouple should open.
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This message is displayed when the input voltage to the ADC
has fallen below the lower negative limit of the ADC.