Teledyne T100, Instruction Manual, Page: 246 / 404

Theory Of Operation Teledyne ML - T100 UV Fluorescence SO2 Analyzer
246 06807A(DCNxxxx)
9.5.4. PMT COOLING SYSTEM
The performance of the analyzer’s PMT is significantly affected by temperature.
Variations in PMT temperature are directly reflected in the signal output of the PMT.
Also the signal to noise ratio of the PMT output is radically influenced by temperature
as well. The warmer The PMT is, the noisier its signal becomes until the noise renders
the concentration signal useless. To alleviate this problem a special cooling system
exists that maintains the PMT temperature at a stable, low level.
Figure 9-19: PMT Cooling System
9.5.4.1. THERMOELECTRIC COOLER (TEC)
The core of the T100 PMT cooling system is a solid state heat pump called a
thermoelectric cooler (TEC). Thermoelectric coolers transfer heat from a one side of a
special set of semiconductor junctions to the other when a DC current is applied. The
heat is pumped at a rate proportional to the amount of current applied. In the T100 the
TEC is physically attached to a cold block that absorbs heat directly from the PMT and a
heat sink that is cooled by moving air (refer to Figure 9-19). A Thermocouple embedded
into the cold block generates an analog voltage corresponding to the current temperature
of the PMT. The PMT Preamp PCA conditions and amplifies this signal then passes it
on to the TEC Control PCA.