Teledyne 6200E - Sulfides Analyzer - Manual (Page 224)

Theory Of Operation Model 6200E Instruction Manual
224 M6200E Rev: A1
TEC
Control
PCA
PMT Preamp
PCA
Thermistor
outputs temp of
cold block to
preamp PCA
Preamp PCA sends
buffered and
amplified thermistor
signal to TEC PCA
TEC PCA sets
appropriate
drive voltage
for cooler
Heat from PMT is absorbed
by the cold block and
transferred to the heat sink
via the TEC then bled off
into the cool air stream.
PMT
Cold Block
Hea
t S
in
k
Cooling Fan
ThermoElectric Cooler
Figure 10-15: PMT Cooling System
10.4.5.2. TEC Control Board
The TEC control printed circuit assembly is located on the sensor housing assembly, under the
slanted shroud, next to the cooling fins and directly above the cooling fan. Using the amplified
PMT temperature signal from the PMT preamplifier board (Section 10.4.6), it sets the drive
voltage for the thermoelectric cooler. The warmer the PMT gets, the more current is passed
through the TEC causing it to pump more heat to the heat sink.
TEC Control Power Status LED
A red LED located on the top edge of this assembly glows constantly to indicate that the control
circuit is receiving power.
TEC Control Test Points
Four test points are also located at the top of this assembly they are numbered left to right start
with the point immediately to the right of the power status LED. See Section 11.5.13 for more
information.
10.4.6. PMT Preamplifier
The PMT preamplifier board amplifies the PMT signal into a useable analog voltage (PMT) that can
be processed by the motherboard into a digital signal to be used by the CPU to calculate the H
2
S
concentration of the gas in the sample chamber.
The output signal of the PMT is controlled by two different adjustments. First, the voltage across
the electron multiplier array of the PMT is adjusted with a set of two hexadecimal switches.
Adjusting this voltage directly affects the HVPS voltage and, hence, the signal from the PMT.
Secondly, the gain of the amplified signal can further be adjusted through a potentiometer. These