Omega CYD200 Series, User Manual

Omega Model CYD201/202 User’s Manual 

2-8 Installation 

2.4 

SENSOR INSTALLATION RECOMMENDATIONS 

Abbreviated sensor installation recommendations for the Model CYD201 are 

included in this section. Please refer to the Omega Product Catalog for 

sensor specifications. Call Omega for copies of application notes or with 

questions or comments concerning sensor installation. 

1.  Do not ground the sensor. 
2.  Shield leads and connect shield wire to SHIELD on screw terminal 

connector only. Do not connect shield at other end of cable. 

3.  Keep leads as short as possible. 
4.  Use twisted-pair wire. Use Omega Duo-Twist™ wire (or equivalent) for 

two-wire, or Quad-Twist™ wire (or equivalent) for four-wire applications. 

5.  Thermally anchor lead wires. 

2.4.1 

Two-Lead Measurement Considerations 

In two-lead measurement, the leads measuring sensor voltage are also the 

current carrying leads. The resultant voltage measured at the instrument is 

the sum of the temperature sensor voltage and the IR voltage drop within 

the two current leads. In a cryogenic environment, the heat flow down the 

leads is of critical concern, so wire of small diameter and significant 

resistance per foot is preferred to minimize heat flow. Consequently, a 

voltage drop within the leads may exist. 

Expect some loss in accuracy since the voltage measured at the voltmeter 

is the sum of the sensor voltage and the voltage drop across the connecting 

leads. The exact measurement error depends on sensor sensitivity and 
variations resulting from changing temperature. For example, a 10 

Ω

 lead 

resistance results in a 0.1 mV voltage error. The resultant temperature error 

at liquid helium temperature is only 3 mK, but because of the lower 

sensitivity (dV/dT) of the diode at higher temperatures, it becomes 10 mK at 

liquid nitrogen temperature. 

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.