Pmt Cooling System; Figure 12-19: Pmt Cooling System - Teledyne t100 Operation Manual

Principles of Operation
12.5.4.

PMT COOLING SYSTEM

TEC PCA sets
appropriate
drive voltage
for cooler
12.5.4.1. THERMOELECTRIC COOLER (TEC)
288
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.
TEC
Control
PCA
ThermoElectric Cooler
Cooling Fan

Figure 12-19: PMT Cooling System

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 12-19). 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.
Teledyne API - T100 UV Fluorescence SO
Preamp PCA sends
buffered and
amplified thermistor
signal to TEC PCA
(TEC)
PMT
Cold Block
Heat form PMT is absorbed
transferred to the heat sink
via the TEC then bled off
into the cool air stream.
PMT Preamp
PCA
Thermistor
outputs temp of
cold block to
preamp PCA
by the cold block and
06807F DCN7335
Analyzer
2