Integral temperature and liquid level sensor and control

• US 5,178,009 A
• Filed: 05/21/1991
• Issued: 01/12/1993
• Est. Priority Date: 03/08/1990
• Status: Expired due to Fees

• Current Assignee: Industrial Engineering & Development Incorporated
• Original Assignee: Industrial Engineering & Development Incorporated
• Inventors: Holden, Thomas, Bryan, Donald G. Jr., Arekapudi, Anil K.
• Primary Examiner(s): YASICH, DANIEL
• Application Number:
  US07/705,011
• Time in Patent Office: 602 Days
• Field of Search: 73/292, 73/295, 137/389, 137/391, 137/392, 340/620, 374/142
• US Class Current: 73/292
• CPC Class Codes: G01F 23/241 for discrete levels
• CPC Class Codes: G01F 23/243 Schematic arrangements of probes combined with measuring circuits
• CPC Class Codes: G01K 7/22 the element being a non-linear resistance, e.g. thermistor G01K7/26 takes precedence
• CPC Class Codes: Y10T 137/7297 With second diverse control
• CPC Class Codes: Y10T 137/8342 Liquid level responsive indicator, recorder or alarm

Abstract

A temperature controller with an integral liquid level control is contained within one unit. The unit consists of an electrical and heat conductive housing, which serves as a first electrode of the liquid level sensor. A metal clamp and a means to attach the housing to the liquid vessel is insulated from the housing and serves as a second electrode. The electrodes are connected in an electrical circuit such that when the electrodes are immersed within a conductive liquid, the resistance between the electrodes is reduced and a current is allowed to flow. A temperature sensor, such as a thermistor, RTD, or thermocouple, is contained within the housing. The housing conducts heat from the housing environment for radiation within the housing.

Claims

1. A controller for receiving sensor output from an integral temperature and liquid level sensor and controlling a liquid level and the temperature of the liquid, the controller comprising:

means for receiving an input information signal from an integral temperature and liquid sensor means, the input information signal corresponding to a liquid level signal generated by a conductive portion of a housing of the integral temperature and liquid level sensor and a liquid temperature signal generated by a temperature sensor within the housing portion of the integral temperature and liquid level sensor;

a power source for providing power for a controller and a liquid level sensor;

the controller including means for providing a temperature set point;

means for processing the input information signals corresponding to the liquid level signal and the temperature signal;

means for energizing a heater when the integral temperature and liquid level sensor input signals to the controller correspond to the liquid level signal and the temperature signal from the sensor indicating a liquid temperature below the set point and a liquid level sufficient to complete a circuit including the conductive portion of the housing of the integral temperature and liquid level sensor resulting in the conductive portion of the housing providing the signal corresponding to the liquid level;

means for de-energizing the heater when the integral temperature and liquid level sensor input signal to the controller corresponds to either the liquid level signal from the sensor indicating a liquid level below the conductive portion of the housing providing the signal corresponding to the liquid level or the temperature signal to the controller from the temperature sensor within the housing portion of the integral temperature and liquid level sensor corresponds to a liquid temperature above the set point.

3. A controller as set forth in claim 1 wherein the temperature set point is adjustable.

4. A controller as set forth in claim 1 wherein timer means introduces a time delay to prevent rapid cycling of the signals generated by the integral temperature and liquid level sensor for input to the controller means which can occur due to movement of the liquid relative to the conductive portion of the housing providing the signal corresponding to the liquid level.

5. A controller as set forth in claim 4 wherein the timer means time delay is adjustable.

6. A controller as set forth in claim 1 wherein the controller power source provides a relatively high frequency and low voltage sensor operating characteristic, wherein the chosen frequency range reduces the effect of electrolysis.

7. A controller as set forth in claim 6 wherein the frequency is at least 10K HZ.

2. A controller as set forth in claim further comprising:

a liquid refill valve; and

means for energizing the liquid refill valve when the integral temperature and liquid level sensor input signals to the controller from the integral temperature and liquid level sensor correspond to a condition in which the liquid temperature is below the set point and the liquid level is below the conductive portion of the housing providing the signal corresponding to the liquid level.

8. A process control method for receiving an output from an integral temperature and liquid level sensor as an input to the process control method, the integral temperature and liquid level sensor including an integral temperature sensor within a housing portion and a liquid level sensor including a conductive housing portion of the integral temperature and liquid level sensor, the steps of the method comprising:

providing an integral temperature and liquid level sensor, the integral temperature and liquid level sensor including a housing having conductive portions and a temperature sensor within the housing;

generating a temperature information input signal based upon a fluid temperature sensed by the temperature sensor within the housing;

generating a liquid level signal based upon immersion of at least a portion of the conductive portion of the housing of the integral temperature and liquid level sensor in a liquid;

providing a power source for the integral temperature and liquid level sensor means and an associated process controller;

providing the associated process controller with a temperature set point;

transmitting the temperature and liquid level signals from the integral temperature and liquid level sensor to the process controller;

processing the temperature and liquid level signals;

energizing a heater when the temperature and liquid level signals from the integral temperature and liquid level sensor to the process controller corresponds to a liquid temperature below the temperature set point and a liquid level sufficient to close a circuit including the conductive portion of the housing of the integral temperature and liquid level sensor; and

de-energizing the heater when either the temperature and liquid level signals from the integral temperature and liquid level sensor means corresponds to a liquid temperature above the provided temperature set point, or the liquid level signal from the integral temperature and liquid level sensor corresponds to a liquid level sufficiently below the conductive portion of the housing of the integral temperature and liquid level sensor so that the circuit including the conductive portion of the housing of the integral temperature and liquid level sensor is open.

9. A method as set forth in claim 8 further comprising:

energizing a liquid refill valve when the input signal corresponds to a condition in which the liquid temperature is below the set point and the liquid level is insufficient to close the circuit including the conductive portion of the housing of the integral temperature and liquid level sensor.

10. A method as set forth in claim 8 including the step of adjusting the temperature set point.

11. A method as set forth in claim 8 including the steps of:

introducing a time delay in the process controller; and

preventing rapid cycling of the heater due to fluctuating liquid level signals from the integral temperature and liquid level sensor which can occur due to movement of the liquid relative to the conductive portion of the housing of the integral temperature and liquid level sensor that does not correspond to a change in the level of the liquid being sensed.

12. A method as set forth in claim 11 including the step of adjusting the length of the time delay.

13. A method as set forth in claim 8 including the steps of:

operating the power source at a relatively high frequency;

operating the integral temperature and liquid level sensor at a relatively low voltage; and

selecting a frequency range for the power source so as to reduce the effect of electrolysis.

14. A method as set forth in claim 13 including the step of selecting a frequency of at least 10K HZ.