Thermal Calibration

Thermal Calibration Baths

SCHWING has found that fluidized bed processing is an excellent method for low-temperature heat treatment processes – like stress relief, shape-setting, and tempering. Thermal uniformity of the bed ensures even temperatures across the entire work piece, and rapid heat transfer characteristics of the fluidized bed allow for quick processing and constant throughput of parts.


Technical Basics

Air or inert gas is introduced from below, through a special diffusion plate, into a retort with fine-grain aluminum oxide, mixing intensively with the solids. This creates a fluidized bed in the measuring chamber (retort) where the Al2O3 solid particles move at low gas velocities without significant kinetic energy. The fluidized bed in the retort conducts heat extremely well and because of its mass possesses an enormous heat capacity. Test specimens such as thermocouples or other sensors can be immersed without issue.

The calibration and test system THERMOCAL is heated indirectly via electric heaters and can be used over a large temperature range from 100° F to 2,000° F with top precision. The precise calibration process of THERMOCAL, which can be reproduced at any time, is handled by an electronic controller with thermocouples and direct measured value indication.

Many times an oil bath, which soils the temperature measuring instruments, is used for conventional calibration. The Al2O3 powder used for the THERMOCAL calibration bath, by contrast, is odorless, non-toxic, non-flammable, neither corrosive nor aggressive and particularly clean in handling and above all, it does not leave any oil or salt residues on the test specimen.


Calibration and adjustment of temperature probes and thermal instruments are tasks requiring precision. Achieving the required accuracy requires measuring and testing devices that ensure high temperature uniformity over the entire working range. The waste gas-free fluidized bed calibration bath THERMOCAL TH 050 is suited for this requirement. It works in a temperature range above room temperature up to 1,100° F at a bath constancy with only minimal fluctuations of ± 0.3° F for short-term and ± 0.55° F for long-term applications. The useful retort volume is 6 inches diameter by 12 inches deep.

The THERMOCAL retort, a cylindrical container from stainless steel, as well as all required measuring and control devices are accommodated by a single compact housing. The retort is completed by a diffusion plate through which the compressed air is finely distributed. In addition, it is equipped with a dual jacket through which the fluidization air is routed and heated. The temperature measurement device is located in the lower area of the retort.

The devices are equipped with two separate heaters as standard. The external heater, consisting of two heating bands, allows quick heating according to the position of the pertaining selector switch. It also serves as back-up heater at bath temperatures above 650° F. The control heater, designed as a tubular heating element, is located directly inside the retort. The temperature is controlled via an electronic controller with thermocouples with analog or digital setting as well as a deviation or direct indicator.

THERMOCAL TH 500-12 System

With retort dimensions of 12 inches in diameter by 20 inches deep, gas-free and environmentally friendly system THERMOCAL TH 500-12 offers approximately seven times the capacity of the TH 050 and is therefore suitable for the calibration of larger instruments.

The fluidized bed calibration bath THERMOCAL TH 500-12 works in temperature ranges up to 2,000° F. It achieves a bath constancy of ± 2° F as well as a short-term stability of ± 1.6° F.

Want to learn more? Contact us using our online form today!

Contact Form