FLUKE 7103-TR-156 User Manual for the Fluke 7103 Liquid Bath Calibrator, 86 to 257°F

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7103 Micro-Bath User’s Guide

Bath Fluid

Viscosity8.3.2

Viscosity is a measure of the thickness of a uid, how easily it can be poured and

mixed. Viscosity affects the temperature stability of the bath. With low vis cosity,

uid mixing is better which creates a more uniform temperature throughout the bath.

This improves the bath response time which allows it to maintain a more constant

temperature. For good control the viscosity should be less than ten centistokes. Twenty

centistokes is about the upper limit of allow able viscosity. Viscosities greater than this

cause very poor control stability and may also overheat or damage the stirring motor.

With oils viscosity may vary greatly with temperature.

When using uids with higher viscosities the controller proportional band may need to

be increased to compensate for the reduced response time. Otherwise the temperature

may begin to oscillate.

Specic Heat8.3.3

Specic heat is the measure of the heat storage ability of the uid. Specic heat, to a

small degree, affects the control stability. It also affects the heating and cooling rates.

Generally, a lower specic heat means quicker heating and cooling. The proportional

band may require some adjustment depending on the specic heat of the uid.

Thermal Conductivity8.3.4

Thermal conductivity measures how easily heat ows through the uid. Ther mal

conductivity of the uid affects the control stability, temperature unifor mity, and probe

temperature settling time. Fluids with higher conductivity distribute heat more quickly

and evenly improving bath performance.

Thermal Expansion8.3.5

Thermal expansion describes how the volume of the uid changes with temper ature.

Thermal expansion of the uid used must be considered since the in crease in uid

volume as the bath temperature changes may cause overow. Excessive thermal

expansion may also be undesirable in applications where constant liquid level is

important. Many uids including oils have signicant thermal expansion.

Electrical Resistivity8.3.6

Electrical resistivity describes how well the uid insulates against the ow of electric

current. In some applications, such as measuring the resistance of bare temperature

sensors, it may be important that little or no electrical leakage oc cur through the uid.

In such conditions choose a uid with very high resistivity.

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FLUKE 7103-TR-156 7103 Liquid Bath Calibrator, 86 to 257°F