Omega Speaker Systems CY670 Series Manual De Usuario

 
 

Three aspects of using a temperature sensor are 
critical to its optimum performance: 

•  the proper electrical and thermal installation of 

the connecting leads that run to the sensor 

•  the actual mounting of the sensor to the sample 

assembly 

•  the measurement electronics used for reading 

and recording temperature data from the sensor 

 

Although the majority of the CY7/CY670 series 
sensors are two-lead devices, measurements are 
preferably made using a four-wire configuration to 
avoid all uncertainties associated with lead 
resistance. This is done by using four connecting 
leads to the device and connecting the V+ and I+ 
leads to the anode and the V– and I– leads to the 
cathode as shown in Figure 1. The exact point at 
which the connecting leads are soldered to the 
device leads results in negligible temperature 
measurement uncertainties. 

In a two-wire measurement configuration, the 
voltage connections (point A in Figure 1) are made 
near or at the current source, so only two leads 
are actually connected to the device. Some loss in 
accuracy can be expected since the voltage 
measured at the voltmeter is the sum of the diode 
voltage and the voltage drop across the 
connecting leads. The exact temperature 
uncertainty will depend on the temperature range 
and lead resistance. For a 10-ohm lead 
resistance, the diode voltage will be offset by 0.1 
mV, which gives a negligible temperature error at 
liquid helium temperature but a 50 mK error near 
liquid nitrogen temperature. Note the PI and CY 
adapter can be used only in a two-wire 
configuration.

An excessive heat flow through the connecting 
leads to any temperature sensor can create a 
situation where the active sensing element (for the 
CY7/670 series this is the diode chip) is at a 
different temperature than the sample to which the 
sensor is mounted. This is then reflected as a real 
temperature offset between what is measured and 
the true sample temperature. Such temperature 
errors can be eliminated by proper selection and 
installation of the connecting leads. 

In order to minimize any heat flow through the 
leads, the leads should be 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 poor thermal 
conductivity yet the resistivities are not so large as 
to create any problems in four-wire 
measurements. 

Lead wires should also be thermally anchored at 
several temperatures between room temperature 
and cryogenic temperatures to guarantee that heat 
is not being conducted through the leads to the 
sensor. A final thermal anchor at the sample itself 
is a good practice to assure thermal equilibrium 
between the sample and the temperature sensor. 
Note that the CU, CY, SO, and DI mounting 
adapters serve as their own sample thermal 
anchor. 

I the connecting leads have only a thin insulation 
such as vinyl acetal or other varnish type coating, 
a simple thermal anchor can be made by winding 
the wires around a copper post or other thermal 
mass and bonding them in place with a thin layer 
of CYAV varnish. There are a variety of other 
ways in which thermal anchors can be fabricated; 
a number of guidelines can be found in detail in 
the following references.