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OMEGA Model CYD201/CYD208 User’s Manual
2-4 Installation
2.4.2 Connecting Leads To The Sensor
Excessive heat flow through connecting leads to any temperature sensor
may differ the temperature between the active sensing element and the
sample to which the sensor mounts. This reflects as a real temperature
offset between what is measured and the true sample temperature.
Eliminate such temperature errors with proper selection and installation of
connecting leads.
To minimize heat flow through the leads, select leads of small diameter and
low thermal conductivity. Phosphor-bronze or Manganin wire is commonly
used in sizes 32 or 36 AWG. These wires have a fairly low thermal
conductivity, yet electrical resistance is not large enough to create
measurement problems.
Thermally anchor lead wires at several temperatures between room
temperature and cryogenic temperatures to guarantee no heat conduction
through the leads to the sensor.
2.4.3 Sensor Mounting
Before installing a diode sensor, identify
which lead is the anode and which is the
cathode. When viewed with the base down
and the leads towards the observer, the
anode is on the right and the cathode is on
the left. The OMEGA CY-7-SD silicon diode
sensor lead configuration is shown to the
right. For other sensors, read accompanying
literature or consult the manufacturer to
positively identify sensor leads. Lead identification should remain clear even
after sensor installation. Record the sensor serial number and location.
On the CY-7-SD, the base is the largest flat surface. It is sapphire with gold
metalization over a nickel buffer layer. The base is electrically isolated from
the sensing element and leads; make all thermal contact to the sensor
through the base. A thin braze joint around the sides of the SD package
electrically connect to the sensing element. Avoid contact to the sides with
any electrically conductive material.
When installing the sensor, make sure there are no electrical shorts or
current leakage paths between the leads or between the leads and ground.
If IMI-7031 varnish or epoxy is used, it may soften varnish-type lead
insulations so that high resistance shunts appear between wires if
sufficient
time for curing is not allowed
.
Slide Teflon
®
spaghetti tubing over bare leads when the possibility of
shorting exists. Avoid putting stress on the device leads and allow for
thermal contractions that occur during cooling which could fracture a solder
joint or lead if installed under tension at room temperature.
DT-470-SD
Diode Sensor Leads
Anode
Cathode