System and method for heater control for evaporation of cryogenic fluids for cooling scientific instruments

• US 5,973,299 A
• Filed: 09/11/1997
• Issued: 10/26/1999
• Est. Priority Date: 11/01/1996
• Status: Expired due to Term

• Current Assignee: Waters Technologies Corporation (Waters Corporation)
• Original Assignee: TA Instruments, Inc. (Waters Corporation)
• Inventors: Reader, John R. Jr.
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US08/927,879
• Time in Patent Office: 775 Days
• Field of Search: 219/497, 219/499, 219/501, 219/483-486, 219/508, 219/506, 374/11, 374/33, 374/31, 374/12, 323/235, 323/236
• US Class Current: 219/486
• CPC Class Codes: G05D 23/1919 characterised by the type of controller

Abstract

A heater controller for allocating heaters to cool a thermal chamber of a scientific instrument evaporates cryogenic liquid to produce a coolant gas. The gas is injected into a chamber to cool a sample disposal therein. The controller allocates low-capacity heaters in compliance with IEC guidelines to prevent problems generally associated with switching of large current loads, such as heaters. In one embodiment, heaters are activated so as to avoid jump discontinuities by effectively averaging the power delivered by the heaters. A second embodiment reduces complexity by essentially disregarding the problem of the jump discontinuity. A third embodiment groups the heaters according to a binary grouping scheme. The heater controller of the present invention can be used to control temperature according to a user supplied temperature profile.

Claims

1. A cooling system, comprising:

a dewar containing a cryogenic liquid;

a microprocessor, comprising a watts-desired register in a value representing a desired heater power delivery is stored;

one or more low-capacity heaters conforming to a loading standard, coupled to said microprocessor through one or more heater control elements, said low-capacity heaters disposed in said cryogenic liquid;

one or more high-capacity heaters coupled to said microprocessor through one or more additional heater control elements, said high-capacity heaters disposed in said cryogenic liquid; and

a heater control process controlling said heater control elements to activate said one or more low-capacity heaters and said one or more high capacity heaters according to said value stored in said watts desired register.

2. The cooling system of claim 1, wherein said one or more high-capacity heaters comprise a plurality of low-capacity heaters combined to form said high-capacity heater.

3. The cooling system of claim 1, wherein said heater control elements are triacs.

4. The cooling system of claim 1, further comprising:

a low-capacity heater storage register;

a high-capacity heater storage register; and

means for determining a next heater to activate based on a value stored in said low and high-capacity heater storage registers.

5. The cooling system of claim 1, wherein said heater control process stores a value representing the most recently used low-capacity heater in said low-capacity heater storage register, and stores a value representing the most recently used high-capacity heater storage register.

6. The cooling system of claims 5, wherein said next low-capacity heater to activate is the least recently used of the low-capacity heaters and the next high-capacity to be activated is the least recently used of the high-capacity heaters.

7. The cooling system of claim 2, wherein said plurality of low-capacity heaters form groupings of heaters according to a binary count.

8. The cooling system of claim 1, wherein said low-capacity heaters nominally supply 100 W of power.

9. The cooling system of claim 1, wherein said high-capacity heaters nominally supply 200 W of power.

10. A method for controlling activation of a plurality of heaters of heater subsystem in a temperature control system, comprising the steps of:

(a) determining a desired power to be supplied by the heater subsystem;

(b) storing said desired power as a value in a watts desired register;

(c) activating one of the plurality of heaters when the said value is greater than a power nominally supplied by said heater;

(d) subtracting said power nominally supplied by said heater from said value to obtain a result;

(e) storing said result in said watts desired register as a new value; and

(f) repeating steps (c) and (d) until either (i) there is no heater of the plurality of heaters that is not activated, or (ii) the value remaining in said watts desired register is less than the power nominally supplied by any of the plurality of heaters.

11. The method of claim 10, wherein said heater subsystem includes at least one low-capacity heater and at least one high-capacity heater, further comprising the steps of:

(g) allocating said at least one high-capacity heater in accordance with steps (c)-(e); and

(h) allocating said at least one low-capacity heater according to steps (c)-(e).

12. The method of claim 11, wherein step (h) is performed after step (g).

13. The method of claim 11, further comprising the steps of:

determining a fractional value substantially equal to a quotient resulting from the value stored in the watts desired register divided by the power nominally supplied by a variable heater, said variable heater being one of said plurality of heaters; and

activating said variable heater for a portion of the number of power cycles that are available during which to activate said variable heater such that a second quotient equal to said portion of the number of power cycles divided by said total number of power cycles is substantially equal to said first quotient.

14. The method of claim 11, further comprising the steps of:

(i) grouping said heaters into groups having an increasing binary count; and

(j) activating said groups of heaters in accordance with steps (c)-(e).

15. A heater controller for controlling AC electrical current supplied to one or more heaters disposed in a dewar containing a cryogenic fluid by sending control signals to one or more heater control elements to conduct a sufficient current to one or more heaters to achieve a desired cooling, comprising:

a microprocessor coupled to the heater control elements to activate said heater control elements to conduct a desired amount of current; and

a heater control Process executing on said microprocessor to cause said microprocessor to transmit a control signal to each of said heater control elements to cause current to be conducted to the one or more heaters according to a value stored in a watts desired register such that the activation of the one or more heaters in response to said current conforms with a loading standard; and

wherein said one or more heaters include at least one low-capacity heater and at least one high-capacity heater, further comprising;

a dynamic amount of power that is desired for the heaters to deliver, wherein said heater control process comprises;

a low-capacity heater controller to control activation of said at least one low-capacity heater; and

a high-capacity heater controller to control activation of said at least one high-capacity heater.

16. The heater controller of claim 15, wherein said at least one high-capacity heater comprises a plurality of low-capacity heaters.

17. The heater controller of claim 15, wherein said low-capacity heater controller further comprises:

(a) determining means for determining if the value stored in said watts desired register is less than a power nominally supplied by a low-capacity heater;

(b) means for sending a first control signal to a first one of said heater control elements to supply current to a first one of said low-capacity heaters when said determining means determines that said value is greater than the power nominally supplied by a low-capacity heater;

(c) means for subtracting the power nominally supplied by a low-capacity heater from said watts desired register to generate a first result;

(d) means for storing said first result in said watts desired register;

(e) means for adding a value representative of a user'"'"'s desired watts to said watts desired register to generate a second result; and

(f) means for storing said second result in said watts desired register.

18. The heater controller of claim 17, wherein said low-capacity heater controller further comprises means for applying means (a)-(e) repeatedly until said value is less than the power nominally supplied by a low-capacity heater.

19. The heater controller of claim 15, wherein said high-capacity heater controller further comprises:

(a) determining means to determine if said value is greater than or equal to a power nominally delivered by a high-capacity heater;

(b) means for sending a control signal to one of said high-capacity heaters when said determining means indicates that said value is greater than or equal to the power nominally delivered by a high-capacity heater;

(c) subtraction means for subtracting the power nominally delivered by a high-capacity heater from said watts desired register to generate a result; and

(d) means for storing said result in said watts desired register as said value.

20. The heater controller of claim 19, wherein said high-capacity heater controller further comprises:

means for applying means (a)-(d) repeatedly until said value is less than the power nominally supplied by a high-capacity heater.

21. The heater controller of claim 15, wherein said standard is the IEC standard.