Typical sensor installation in a mechanical refrigerator
Vacuum shroud
Vacuum space
Radiation shield
Second stage and
sample holder
Thermal anchor
(bobbin)
Cryogenic wire
(small diameter, large AWG)
To room
temperature
Refrigerator
first stage
Sensor
Thermal anchor
(bobbin)
Heater
(wiring not shown
for clarity)
Optical window
(if required)
Dental floss
tie-down
-or-
Cryogenic
tape
Drawing not to scale
18
c
HAPTER
2:
Cooling System Design and Temperature Control
Model 335 Temperature Controller
2.4.7 Lead Soldering
When additional wire is soldered to short sensor leads, care must be taken not to
overheat the sensor. A thermal anchor such as a metal wire clamp or alligator clip will
anchor the leads and protect the sensor. Leads should be tinned before bonding to
reduce the time that heat is applied to the sensor lead. Solder flux should be cleaned
after soldering to prevent corrosion or outgassing in vacuum .
2.4.8 Thermal
Anchoring Leads
Sensor leads can be a significant source of error if they are not properly anchored.
Heat will transfer down even small leads and alter the sensor reading. The goal of
thermal anchoring is to cool the leads to a temperature as close to the sensor as possi-
ble. This can be accomplished by putting a significant length of lead wire in thermal
contact with every cooled surface between room temperature and the sensor. Lead
wires can be adhered to cold surfaces with varnish over a thin electrical insulator like
cigarette paper. They can also be wound onto a bobbin that is firmly attached to the
cold surface. Some sensor packages include a thermal anchor bobbin and wrapped
lead wires to simplify thermal anchoring.
FIGURE 2-1
