Compact temperature control for medical equipment

The trend to miniaturize medical diagnostic and analytical instrumentation has led engineers to pack more functionality into a tighter space. Packing electronics in a smaller footprint increases heat flux, leading to thermal challenges. This waste heat requires efficient management to meet conflicting requirements of increased performance, reduced power consumption, and quieter operation in a compact design. For systems that require refrigeration for specific reaction temperatures – such as benchtop incubators, laboratory centrifuges, chromatography, and clinical chemistry analyzers – temperature control systems play an important role in performance, size, and improved test results.

Thermoelectric assemblies (TEAs) with integrated temperature control can meet the increasing thermal challenges. Below are some examples.

Automated blood analyzers and centrifuges: Used in healthcare, forensic, and bioscience labs, this equipment requires colder temperatures to extend reagent life. Formerly, these machines used compressor-based systems or recirculating chillers for thermal control. Many modern systems use TEA-based systems to improve overall system performance in tight spaces.

Immunoassay and clinical chemistry analyzers: Commercial systems for diagnosing diseases, monitoring diseases, and testing drugs can analyze hundreds of different parameters in patient fluid samples, using chemical reactions to quantify substances such as glucose, cholesterol, proteins, and enzymes. Immunoassay analyzers can also detect and quantify chemical substances in patient samples. These systems, however, are designed to measure the concentration of a substance using the reaction of an antibody to its antigen. Standalone clinical chemistry and immunoassay analyzers and integrated systems also perform both tests. Analyzers require reaction reagents, often stored on the system. Reagent chambers cooled to increase reagent shelf life are typically held at a constant temperature between 4°C to 8°C. TEAs can cool the reagent chamber as an alternative to conventional compressor-based systems.

Liquid chromatography: A technique for analyzing mixtures by separating, identifying, and quantifying their constituent components, liquid chromatography normally operates with smaller amounts of fluids and measures the relative proportions of analytes in a mixture. Temperature control is important in sample storage while samples are waiting to be analyzed.

Two major uses of thermoelectrics in controlling the temperature of high-performance liquid chromatography (HPLC) instruments are temperature control of the sample storage compartment by thermoelectric cooling and heating, and heating and cooling the separation column. In modern HPLC equipment, thermal management systems provide temperature stability and condensation protection. Depending on the mixture, precise temperature control from 4°C to 40°C is required. Heat load requirements typically range from 20W to 100W, with some newer machines requiring cooling up to 200W to increase sample testing throughput. Many new HPLC instruments feature multiple sample storage chambers that have different cooling/heating requirements, increasing overall system heat load.

TEA

To answer heat challenges caused by miniaturization, Laird TEA products include a series with higher capacity in a small package. Changes boost the Tunnel series TEAs cooling capacities to more than 100W to support larger chamber and storage compartments. Available in compact 12V and 24V configurations, the series fits inside medical diagnostics and analytical instrumentation with tight constraints.

Featuring air-to-air or direct-to-air heat transfer mechanisms designed to move air across heat sinks vs. traditional impingement flow, the series reduces the required airflow paths to accommodate tight space constraints. Thermoelectric modules (TEMs) have been optimized for high efficiency and improved reliability. Additional design features include lower noise fans, improved sealing to prevent moisture intrusion, and higher efficiency.

TEAs, when combined with the SR-54 series temperature controller, offer temperature control within ±1°C. The controller also provides temperature monitoring and alarm functions, including identification of fan problems and over-temperature. The controller requires minimal programming and can be easily adhered to a TEA or system enclosure. Reduced fan speeds lower operational noise.

Conclusion

Cooling below ambient temperature is vital in medical diagnostic and analytical instrumentation equipment. Operating machine temperature fluctuations can affect the test results and shorten the life of reagents or samples. Laird’s space-saving thermoelectric assemblies offer temperature stability and condensation protection for analytical and medical instrumentation. The advantages of thermoelectric assemblies include precise temperature control, compactness, faster temperature ramp rates, better efficiency, greater reliability, and lower noise. Laird’s boosted Tunnel Series TEAs meet stringent temperature control requirements and mean-time-before-failure demands of sensitive medical equipment.

Laird Technologies
www.lairdtech.com

About the author: Andrew Dereka is product director at Laird and can be reached at adereka@lairdtech.com.