Instructions, Cernox™ Resistance Temperature
Sensor Installation, CX-10XX-BO Package
Lake Shore Cryotronics, 575 McCorkle Blvd. Westerville, OH 43082
www.lakeshore.com
Phone (614) 891-2243 – Fax (614) 891-1362 –
–
CAUTION:
This temperature sensor is sensitive to electrostatic discharge (ESD). Use ESD
precautionary procedures when handling, or making mechanical or electrical connections to this
device in order to avoid performance degradation or loss of functionality.
There are three aspects of using a cryogenic temperature sensor which are critical to its optimum performance. The first
involves the proper mounting of the sensor package, the second relates the proper joining of sensor lead wires and connecting
wires. The final concern is the thermal anchoring of the lead wires. Although the sequence in which these areas should be
addressed is not set in stone, all elements covered under each aspect should be adhered to for maximum operating
capabilities of the sensor.
SENSOR MOUNTING
The CX- 10XX-BO package combines a standard SD sensor soldered
to a gold-plated copper mounting block. The mounting block of these
packages contain a 3.1 mm (0.122 in) diameter hole designed for
mounting with a #4-40 or M3 screw.
1. A threaded hole in your mounting surface is necessary for mounting
the sensor package. The through hole in the sensor package will
accommodate a #4-40 or M3 brass machine screw. Brass is
recommended due to the thermal contractions/expansions of the
final assembly.
2. Threaded hole and surrounding surface should be cleaned using a
solvent such as acetone followed by an isopropyl alcohol rinse.
Allow time for the solvents to evaporate before mounting.
3. Apply a small amount of Apiezon
®
N grease to the threads of the
screw. To ensure good thermal contact between the sensor and
mounting surface use an indium washer/preform or thin layer of
Apiezon
®
N grease between the mounting surface and the sensor
package.
NOTE:
An overabundance of grease will increase the thermal barrier. Keep the thickness to 0.05 mm or less.
4. Insert screw through sensor mounting block and tighten screw into place.
NOTE:
Ensure that no electrically conductive particles lodge between the mounting block and the SD sensor. There is a
thin braze joint around the sides of the SD sensor that is electrically connected to the sensing element. Contact to the
sides with any electrically conductive material will cause a short. This package is designed for use up to 420 K (146 °C),
subjecting to temperature in excess of this may cause a shift in the sensor values.
LEAD ATTACHMENT
In addition to being soldered to the mounting block, the SD sensor has its leads thermally anchored to the block with a
beryllium oxide heat sink chip. The heat sink chip is used as a buffer layer to take up expansion mismatch between an object
with large expansion coefficient (copper block) and an object with a low expansion coefficient (SD sensor). The BO package
has two 32 AWG phosphor bronze wires, 25 mm (1 in) in length.
BO Package
It is recommended that a 4-lead measurement scheme is used with this sensor. Attaching
four connecting wires to the sensor leads is recommended.
1. Prepare the sensor leads and connecting lead wires with a RMA (rosin mildly active)
soldering flux, tin them with a minimal amount of 60% Sn/40% Pb solder. Use a low
wattage soldering iron that will not exceed 200 °C. Clean off residual flux with rosin
residue remover. The sensing element inside the package should be protected from
excessive heat by putting a heat sink clip over the package.
2. Strip the insulation from the connecting wires by delicately scraping with a razor blade, fine sandpaper, or steel wool.
Phosphor-bronze or manganin wire, in sizes 32 or 36 AWG, is commonly used as the connecting lead wire. These wires
have low thermal conductivity and high resistivity which help minimize the heat flow through the leads. Typical wire
insulation is Formvar™ or Polyimide (ML). Formvar™ insulation has better mechanical properties such as abrasion
resistance and flexibility. Polyimide insulation has better resistance to chemical solvents and burnout.
3. Attach one sensor lead with two of the connector wires and apply the soldering iron above the joint area until the solders
melt, then remove the iron immediately. Repeat for the other set of connector wires and the other sensor lead. Leave
Leads: 0.5 mm diameter by 25 mm long
Total mass: 1.5 g
3.1 mm diameter,
for 4-40 or M3
machine screw
Beryllium oxide
heat sink chip
CX-10XX-SD
sensor
