In my experience, the spike in the readings may have been caused by several different possible causes.
One option may have been that due to a loose wire, there may have been a temporary disconnection. This will be reported as a positive full scale reading with an error (33489 Open Thermocouple detected). A second scenario I have seen, is a bad reading when using unshielded thermocouples that are near motors or other electrically noisy devices and they are starting or stopping. A third cause I have seen of periodic bad readings is a spike in the power supply to the network module. A forth cause, related to the third, is spikes on the power rails going into the FP-TC-120 (for best results, the V&C terminals should not be connected to any other terminal bases or the
network module). Finally, a spike may result from a loss of communication with the network module, although this will normally result in all channels going out of range.
Regards,
Aaron
LabVIEW Champion, CLA, CPI