Calibration bath selection guide

A calibration bath is a uniform temperature enclosure with a constant temperature setting that can be adjusted manually or with automation. These calibration baths use a mixed fluid to provide excellent thermal contact for temperature calibration. They offer high stability, larger working volumes, and flexibility for calibrating a variety of temperature sensors. . This statement is specific to the Fluke analog/digital controllers.

Calibration bath designs

Utility baths

These are low-cost baths that aren’t designed for temperature calibration. Poor temperature uniformity in heat transfer fluid, separate heating and cooling elements, and poor temperature stability make utility baths unsuitable for calibration purposes.

Parallel tube

Parallel tube baths are designed for calibration work. Unlike utility baths, heating and cooling elements are separate from the calibration working area, facilitating efficient mixing of heat transfer fluid. Disadvantages include a small working area and susceptibility to level changes due to fluid expansion and contraction caused by temperature changes.

Concentric tube

This design goes a step beyond the parallel tube design, heating and cooling heat transfer fluid in the outer area where it’s stirred. Then, it pumps fluid into the working area, which is protected from ambient heat losses by the outer tank. The concentric tube design also addresses problems related to stirring fluid at low levels. However, it is still constrained by a small working area.

The concentric tube within a tube design addresses some of the limitations of the parallel tube design. Heating and cooling takes place in the outer area where the fluid is stirred and the temperature controlled. The fluid is pumped into the working area which is guarded from the effect of ambient heat losses by the outer tank. It also solves problems related to stirring problems at low fluid levels. Unfortunately, the concentric tube design still has a limited working area.

*why not keep the original.

Heat port

This bath design offers highly stable and uniform calibration. The cooling coil and the heater are attached to the outside of the bath tank, forming a heat port. Heat port baths have large workspaces, well-balanced stirring mechanisms, and excellent insulation to minimize heat loss .

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Calibration bath specifications

Temperature range

Calibration baths have an advertised temperature range. Depending on the temperature used for calibration, heat transfer fluids must be changed. Rather than using the same heat transfer fluid across the entire temperature range, the fluid must either be switched out or multiple baths must be setup with appropriate fluids at required application temperatures.

Stability

This is the variation in temperature over time. The design of the bath and the controller influence stability. The chosen heat transfer fluid and operating temperature are also factors.

Bath stability describes the variation in temperature over a time period. This can also be influenced by the design of the bath and the controller design. Stability can also change with the fluid you choose and the temperature you operate at.

Uniformity

This is the vertical and horizontal temperature variation in the bath. Uniformity varies with temperature. Bath design and heat transfer fluid viscosity greatly influence uniformity.

Bath uniformity describes vertical and horizontal temperature variation in the working volume of the bath. Uniformity can vary with temperature, bath design, and fluid types.

Tank size

The tank size of a bath determines what size and shape probes you can calibrate. Additionally, if you’re calibrating a large volume of probes, you’ll want a tank size that accommodates that. 

Tank size and fluid volume also impact performance. Larger volume bath typically have better stability and uniformity. However, they are slower responding to temperature change. The opposite is true smaller baths with less volume as they will transition temperature faster but tend to be less stable.

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Compact calibration baths: Low and high temperature 

Standard size calibration baths: Low and high temperature 

Special application

Other