Instructions,
Platinum Resistance Thermometer Installation
Form Number F022-00-00 Revision F — ©2017 Lake Shore Cryotronics, Inc. — 2 May 2017 — Page 3
LEAD ATTACHMENT
1. Although the platinum sensors are 2-lead devices,
measurements should preferably be made using a
4-wire configuration to avoid uncertainties associated
with the resistance of the connecting leads.
2-Lead Measurement Scheme
— The leads used to
measure the voltage are also the current carrying
leads. The resulting voltage measured at the
instrument is the sum of the temperature sensor
voltage and the voltage drop across the two
connecting leads. (See Figure 1A.)
4-Lead Measurement Scheme
— The current is
confined to one pair of current leads with the sensor
voltage measured across the voltage leads. (See
Figure 1B.)
2. Lead Polarity: None.
3. For use up to 500 K, phosphor bronze or Manganin
®
wire in 32 or 36 AWG is commonly used as the
connecting lead wire. These wires have low thermal
conductivity and high resistivity, which helps minimize
the heat flow through the leads. Typical wire
insulation is polyvinyl formal (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. Formvar has a temperature
rating of 373 K while polyimide has a temperature
rating of 505 K.
4. For use above 500 K, use high temperature
connecting wire (e.g., nickel) with high temperature
insulation (e.g., wrap-around, ceramic tube, or
ceramic beaded). Connection should be made by spot
welding or brazing.
5. Platinum sensor leads can easily be soldered if a flux
is used. One suitable flux is Stay Clean
®
Solder and
Tinning Flux (J.W. Harris Company, Cincinnati, Ohio).
Use appropriate solder with respect to temperature
(recommend Sn 60/Pb 40 for up to 400 K and
Pb 90/Sn 10 for up to 500 K.)
6. Stay Clean
®
Solder and Tinning Flux is acidic. Hence,
after soldering, clean off the residual flux with a
solvent that is “basic” in nature (i.e., baking soda
dissolved in water will also work).
7. Join one sensor lead with two of the connector wires.
Apply the soldering iron to the connector wire above
the joint area until the solders melt, then remove the
iron. Repeat for the other set of connector wires and
the other sensor lead.
8. Avoid putting stress on the device leads and leave
enough slack to allow for the thermal contractions that
occur during cooling, which could fracture a solder
joint or lead. Some epoxies and shrink tubing can put
enough stress on lead wires to break them.
9. If the sensor is to be used above 500 K, it is
recommended to either braze or spot weld
appropriate lead wires (e.g., nickel wire).
