Circulating liquid bath with dual reservoir level switch

Abstract

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.

Claims

1. A circulating bath, comprising: a heater configured to be operatively connected to a source of power; a control circuit operatively coupled to the heater; a first fluid level sensor operatively coupled to the control circuit and configured to monitor a low fluid condition; and a second fluid level sensor electrically coupled in series with the first fluid level sensor, and the second fluid level sensor being operatively coupled to the control circuit and configured to monitor the same low fluid condition, a high temperature limit switch operatively coupled to the control circuit, wherein the control circuit is configured to disconnect the heater from the source of power in response to the control circuit receiving a signal from the high temperature limit switch of an over temperature condition, and wherein the control circuit is further configured to disconnect the heater from the source of power in response to the control circuit receiving a signal from either of the first and second fluid level sensors indicative of the same low fluid condition.

2. The circulating bath of claim 1, wherein the high temperature limit switch is electrically coupled in series with the first and second fluid level sensors.

3. The circulating bath of claim 1, wherein the high temperature limit switch and first fluid level sensor are coupled to the control circuit through a first connector, and the second fluid level sensor is coupled to the control circuit through a second connector different than the first connector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.

(2) FIG. 1 is a perspective view of a circulating bath according to an embodiment of the invention.

(3) FIG. 2 is a diagrammatic cross-sectional front view of the circulating bath shown in FIG. 1 according to an embodiment of the invention.

(4) FIG. 3 is a diagrammatic cross-sectional side view of the circulating bath shown in FIG. 1 according to an embodiment of the invention.

(5) FIG. 4A is a schematic of the circulating control circuit including level and temperature control circuits according to an embodiment of the invention.

(6) FIG. 4B is a schematic of the circulating control circuit including level and temperature control circuits according to an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(7) Embodiments of the invention are generally related to a circulating bath designed to meet the requirements for a small footprint, high heater power, variable pump performance, and robust refrigeration system. To provide high heater power in a circulating bath having a reduced footprint, the heating elements may be compact and have high a wattage density. A low level detection circuit including two separate and independent level sensors allows the circulating bath to satisfy the testing requirements of UL 61010-1 without sacrificing desirable footprint and heater performance characteristics of the circulating bath. The second fluid level switch provides a redundant fluid level monitoring ability so that in the event one of the fluid level switches fails, the control circuit will still disconnect power to the heater in response to a low fluid level condition. Embodiments of the invention thus have two separate and independent fluid level switches which monitor the reservoir or reservoir fluid level. Both fluid level switches are configured to close on a fluid rise and are electrically coupled in series. The fluid level switches may be configured so that both switches are coupled to the control circuit through a single connector. In an alternative embodiment, each fluid level switch may be coupled to the control circuit through a separate connector. In yet another embodiment, one fluid level switch may be connected in series with the high temperature limit switch so that the fluid level switch and high temperature limit switch are both coupled to the control circuit though the same connector. The two fluid level switches may also be coupled to a limit circuit in the control circuit so that the heater power cutoff is not dependent on software control. In this way, the circulating bath may shut down the heater when a low level fault condition occurs even if there is a software fault.

(8) Referring now to FIGS. 1-3, in which like reference numerals refer to like elements, an exemplary circulating bath includes a control circuit 12 coupled to a first fluid level sensor or switch 14, a second fluid level sensor or switch 16, and a heater 18. The first and second fluid sensors or switches 14, 16 may comprise a low level detection circuit 19 operatively coupled to the control circuit 12 as shown in FIG. 4A. The heater 18 may include a hot zone or coil 20 configured to be immersed in a fluid 34 contained within a reservoir 22, and cold legs 24, 26 that operatively couple the coil 20 to the control circuit 12. The control circuit 12 and a portion of a circulating pump 29 may be enclosed by a housing 28 that is located on top of a reservoir housing 30. A high temperature limit bulb 32 may be fixed to one of the cold legs (illustrated in this representative embodiment as cold leg 24). The bulb 32 may be part of a high temperature limit device that includes a diaphragm activated switch that is operatively coupled to the control circuit 12. An example of a commercially available high temperature limit device includes part number 97.55134.116 available from EGO North America, Inc. of Newman Ga., United States. Advantageously, by mounting the high temperature limit bulb 32 to a cold leg 24, 26 of the heater 18, the high temperature limit circuit 35 may better monitor the temperature of the fluid 34. This may provide two benefits. The first is that the high temperature limit circuit 35 may monitor fluid temperature more accurately since the bulb 32 is not in contact with a hot heater surface. Secondly, this bulb mounting position may prevent premature heater cutoff due to issues with the heat removal rate from the heater 18 under all operation conditions with different fluids and pump speeds.

(9) Circulating bath 10 may be used to circulate the fluid 34 between the reservoir 22 and an application 36, such as a heating or cooling jacket, in a known manner. To this end, the fluid 34 contained in the reservoir 22 may be drawn out of the reservoir 22 and conveyed to the application 36 via the circulation pump 29, and returned to the reservoir 22 from the application 36 in a closed-loop manner. In certain applications, the fluid 34 may be heated to a predetermined temperature in the reservoir 22 by the heater 18, which is at least partially immersed in the fluid 34, before the fluid 34 is conveyed to the application 36.

(10) The control circuit 12 may include a temperature control circuit 39 configured to control the operation of the heater 18 to a desired temperature set point as is known in the art. In operation, the user may set a desired temperature for the fluid 34 through a user interface 38 including a control interface 40 and a display 42 accessible from outside the housing 28. The circulating bath 10 may also include a temperature sensor 44 (FIG. 4), such as a thermocouple, that is immersed in the fluid 34. The temperature sensor 44 may be coupled to the control circuit 12 and generate a signal indicative of the temperature of the fluid 34. In response to the signal from the temperature sensor 44, the control circuit 12 and/or temperature control circuit 39 may control the heat generated by the heater 18 so that the fluid 34 reaches and is maintained at the desired set point temperature.

(11) Referring now to FIG. 4A, the control circuit 12 is illustrated according to one embodiment including a limiter circuit 46 and the temperature control circuit 39. The limiter circuit 46 includes a first electrically operated switch 48, such as a relay, operatively coupled to the first fluid level switch 14, the second fluid level switch 16, a direct current (DC) power supply 50, and a high temperature limit switch 52. The switch contacts of the relay 48 may couple the heater 18 to a suitable source of electric power, such as a 115 volt 60 hertz alternating current (AC) power line 54. The limiter circuit 46 is thereby configured so that the electrically operated switch 48 disconnects the AC power line 54 from the heater 18 if one or more of the first fluid level switch 14, second fluid level switch 16, or high temperature limit switch 52 is placed in an open state.

(12) The temperature control circuit 39 may include a processor (not shown) and/or another electrical circuit that receives signals from the temperature sensor 44. The temperature control circuit 39 may also include a second electrically operated switch 56 (shown in representative form as a triac) and be operatively coupled to the user interface 38. The temperature control circuit 39 may be configured to receive input from the user interface 38 that defines a desired temperature set point for the fluid 34 contained within the reservoir. Based on signals received from the temperature sensor 44, the temperature control circuit 39 may selectively activate the heater 18 by closing the second electrically operated switch 56 so that the fluid 34 is warmed to the desired set point temperature. To this end, the temperature control circuit 39 may comprise a controller that uses a combination of one or more proportional, integral, and/or derivative control mechanisms as is known in the art of closed loop control systems.

(13) In a specific embodiment of the invention, the first and second fluid level switches 14, 16 are dual level devices including a float and multiple switches in a single device. An example of a commercially available fluid level switch includes part number L312C6805-001 available from Innovative Solutions of Naugatuck, Conn., United States. Each of the first and second level switches 14, 16 is independent of the other switch, and has two sets of electrical connections that couple the switch to the control circuit 12. Each level switch 14, 16 may be utilized to monitor two conditions. The first condition may be a low level warning which informs the end user that the fluid 34 is getting low. The second condition may be a low level fault which shuts off the heater 18 and provides a fault status to the user in response to a low fluid level condition. The low level warning may be controlled through a software application running on a processor in the control circuit 12, and/or the low level fault may be controlled through a dedicated circuit in the control circuit to shut off the heater 18 without the use of software. The control circuit 12 may also include a software application running on a processor that acts as a software cutoff switch. To this end, the software application may monitor or sample signals from the temperature sensor 44 and cut off the heater 18 if the temperature of the fluid 34 rises above an upper threshold.

(14) Referring now to FIG. 4B, in which like reference numerals refer to like elements in FIGS. 1-3 and 4A, an alternative embodiment of the invention is presented. The control circuit 12 in FIG. 4B operates in essentially the same manner as described above with respect to FIG. 4A, except that the second fluid level switch 16 is relocated to share a connector 58 with the high temperature limit switch 52. By coupling the first and second fluid level switches 14, 16 to the control circuit 12 through separate connectors 58, 60, the control circuit 12 may cut off the heater under a low fluid condition even if there is a short across one of the connectors 58, 60.

(15) While the invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative methods, and illustrative examples shown and described herein. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.