Circulating liquid bath with dual reservoir level switch
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Solution Overview
Problem
Conventional circulating baths face challenges in preventing overheating due to thermal lag in high temperature limit bulbs and reduced surface dimensions, especially in compact designs, which can lead to temperature overshoot and failure to meet safety standards like UL 61010-1, particularly when a single failure occurs, such as a faulty reservoir level switch.
Innovation Solution
A circulating bath system with two independent fluid level sensors and a high temperature limit switch, where the control circuit disconnects the heater power in response to signals from either sensor, ensuring safe operation even if one sensor fails, and the high temperature limit bulb is mounted on a cold leg to improve temperature monitoring accuracy and prevent premature heater cutoff.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single fluid level sensor is used in conventional circulating baths, then the device complexity is reduced, but the reliability of overheating prevention deteriorates due to potential sensor failure
Solution Approach 1:
The fluid level sensing function is segmented into two independent sensors positioned at different locations within the reservoir. This segmentation ensures that a failure of one sensor does not compromise the overall safety system, as the second sensor continues to provide monitoring coverage.
Solution Approach 2:
The system incorporates redundant sensing capability in advance to cushion against potential sensor failures. By having two independent sensors, the system prepares for the possibility of one sensor failing, ensuring continuous reliable operation without requiring complex diagnostic or replacement mechanisms.
2Measurement precision
If the high temperature limit bulb is mounted on the heater coil in conventional designs, then the temperature monitoring is simplified, but the measurement precision deteriorates due to thermal lag and reduced surface dimensions
Solution Approach 1:
The temperature monitoring function is extracted from direct contact with the heater coil by mounting the limit bulb on an external cold leg. This extraction eliminates the thermal lag problem caused by mounting on the hot coil surface, allowing the sensor to monitor fluid temperature more accurately without being subjected to excessive direct heat.
Solution Approach 2:
The cold leg serves as an intermediary structure that transmits temperature information from the fluid to the limit bulb without exposing the bulb directly to the high temperatures of the heater coil. This intermediary mounting position provides accurate temperature monitoring while protecting the sensor.
3Area of stationary object
If the circulating bath is designed with compact dimensions, then the footprint is reduced, but the reliability of temperature control deteriorates due to thermal lag and reduced surface area of temperature sensing elements
Solution Approach 1:
The temperature monitoring approach transitions from surface-mounted sensing on the heater coil to a three-dimensional mounting on the external cold leg structure. This dimensional change allows the limit bulb to be positioned optimally for temperature monitoring without being constrained by the limited surface area of compact heater elements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The dual fluid level sensing and high temperature limit switch configuration effectively prevents overheating by ensuring reliable heater disconnection in low fluid or high temperature conditions, meeting safety standards without compromising the compact design's performance and footprint.
Implementation Method 1
As the temperature of the bulb rises, fluid located within the bulb expands. This expanding fluid is typically coupled through a capillary tube to a diaphragm located within the switch housing. When the temperature of the expanding fluid exceeds a set-point temperature, the pressure exerted by the expanding fluid causes an electrical contact within the limit switch to open.
Implementation Method 2
The circulating bath moves the fluid past heating or cooling elements located in the bath reservoir so as to achieve a uniform desired fluid temperature.
Data Source
AI summary
A circulating bath (10) including a heater (18) configured to heat a fluid (34) in a reservoir (22). The heater (18) is configured to be operatively connected to a source of power (50) by a control circuit (39) operatively coupled to the heater (18). First and second fluid level sensors (14) (16) are operatively coupled to the control circuit (39), and provide signals indicative of a low fluid condition in the reservoir (22). The control circuit (39) is configured to receive the signals from the fluid level sensors (14) (16), and disconnect the heater (18) from the source of power (50) in response to receiving a signal from either of the first and second fluid level sensors (14), (16) indicative of a low fluid condition.