“Electrical control” is a specialized discipline of electrical engineering where, to put it simply, electrical circuits and programmable electronics are engineered to turn machines and…
Temperature controls can factor into litigation in a variety of cases including the loss of perishable goods, lost product in manufacturing or processing facilities, fire damage, or personal injury matters involving scalds and burns. In this article, Electrical Engineer, Kenneth J. Kutchek, P.E. and Mechanical Engineer, René Basulto, P.E. provide an introduction to temperature control as it relates to expert witness investigations.
Their discussion includes an overview of temperature control systems, the major components, and potential failures.
Temperature control is a process by which the temperature of a material or space is adjusted and controlled to achieve a desired temperature, or to keep the temperature at setpoint and within safe or desired limits.
Engineers have always been charged with the design of control systems. It was in the 1980’s that controls began a shift towards digital/electronic devices for some types of systems. Design of a control system requires a thorough knowledge and understanding of what is being controlled and how it needs to function.
Today, direct digital controls are widely used in building management systems, HVAC controls, and consumer products. However, pneumatic controls are still commonly used in many large industrial processes and systems.
Temperature control is common in consumer products such as home heating/cooling, space-heaters, refrigerators, water-heaters, dishwashers, coffee pots, ovens/ranges, heating pads, ice makers, and clothes washers/dryers. Vehicles also have multiple temperature control systems including cabin air heating/cooling, seat heaters, and engine and transmission cooling systems.
In industrial applications, temperature control is critical in manufacturing and process systems involving food products, chemicals, electronics, plastics, metals, coatings, and more. The failure to properly control temperature within an industrial process can compromise sanitation, ruin processed material, or in extreme cases cause fires and explosions.
A home heating system is a relatively simple example of temperature control and safety factors that are engineered into the system. The major components are the furnace, which generates heat, and the thermostat, which acts as the brain of the system and performs three primary functions:
The consequences of failure for a home heating system can be severe. The failure to activate the system can cause water damage by way of frozen pipes, or personal injury due to exposure to extreme cold temperatures. On the other end of the spectrum, the failure to deactivate the system can create dangerous fire hazards.
To improve safety, thermostats are engineered with upper and lower operating ranges that reduce the likelihood of extreme temperatures. The furnace also contains a critical temperature control safety device called a high temperature safety cutoff or a combination fan limit control that turns the furnace off if the temperature exceeds a specific upper limit.
Temperature control systems in ovens are designed to maintain a desired temperature for cooking/baking or a broad range of industrial purposes. The major components are the gas burner (for a gas oven) or electric element (for an electric oven), the thermostat, and temperature sensors. Using an electronic or analog input, the user can enter or set a desired temperature setpoint, which the controller references to monitor the current temperature and turn the heating device ON and OFF, or modulate the output as needed. The oven also contains a high temperature safety cutoff, which turns the oven off if it gets excessively hot.
Refrigeration systems can be as small as mini fridges used to store prescription medications, to large scale commercial freezers or refrigerated warehouses. The cost associated with a refrigeration failure in a specialized facility can easily reach millions of dollars and affect global supply chains.
Refrigerators and freezers use a vapor compression cycle to cool by removing heat from the inside air. A temperature sensor measures the temperature of the air in the cooled space. An input allows the user to enter or set a desired temperature setpoint. The controller monitors the current inside temperature and turns the cooling ON and OFF, as needed. Heat is generated and also absorbed through the refrigeration process and a failure of the temperature control system can result in loss of operation and product. A failure of the compressor high temperature safety cutoff along with secondary safeties could cause damage to the compressor resulting in refrigerant contamination, system failure, and loss of product.
Similar to a home furnace, saunas utilize a temperature sensor, controller, and heater. However, a sauna maintains a much higher temperature of 175° to 195°F and typically utilizes a safety shutoff timer. The failure of a sauna to limit temperature and/or regulate exposure has been linked to fatal incidents in individuals. Like other systems mentioned, overheating incidents also have the potential to cause fires.
Many consumer products utilize safety devices to prevent an excessive over-temperature condition where overheating presents a danger.
The type of thermal safety device needed in a product is determined during the engineering and design process. Read the article “Is Your Product Liability Case Really an Electrical Controls Case?” to learn more about where a control systems engineer may benefit your case.
Temperature controls are a critical part of products and processes, because when temperature goes uncontrolled it can lead to burns, property loss, or damaged equipment. Each product, process, or piece of equipment is unique including its design, function, layout, operational requirements, materials processed, and the hazards involved. Therefore, temperature control decisions must be made on a case-by-case basis after a detailed process and risk assessment. Proper temperature control design, manufacturing, programming, installation, calibration, and commissioning are important and must be considered as part of the hazard analysis during product design, system design, and temperature control selection and programming.
The engineers at Robson Forensic regularly investigate equipment, consumer products, industrial machinery incidents, and fires to determine if the cause is related to a temperature control system or component malfunction. The knowledge of how the system is to be controlled is essential to determine these failures. Our engineers have the education, training, and experience to analyze equipment and system failure modes, and determine how temperature control malfunctions contributed to the failure, loss or injury. These investigations typically include an evaluation of the system and electrical design, components, manufacturing, installations, industry standards, maintenance and repair issues, presence of defects, and the adequacy of warnings and instructions.
For more information, submit an inquiry or call us at 800.813.6736.
“Electrical control” is a specialized discipline of electrical engineering where, to put it simply, electrical circuits and programmable electronics are engineered to turn machines and…
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