LI-COR LI-7500, Instruction Manual

Page: 54 / 155

Section 3
Setup and Operation 3-25
Why can't I use the internal thermistor externally?
If a user is interested in improving the temperature readings by measuring near the optical
path, the internal thermistor could be removed from the auxiliary input screw terminals and
soldered to the external auxiliary input cable (blue and gray wires). However, in practice,
radiation loading from sunlight on this unshielded thermistor will result in significant
measurement errors.
The blue and gray wires inside the enclosure are not connected to the green screw terminal
block when the instrument ships from the factory. These wires will need to be connected to
the Auxiliary Inputs terminal prior to using the internal thermistor externally as outlined in
Appendix B.
The polynomial for the thermistor is coded in the instrument software and does not allow user
to substitute another thermistor. In practice the LI-7500 does have two auxiliary inputs but
only one input is available to the user for this reason.