Multiple set point condition monitoring systems

• US 4,799,174 A
• Filed: 10/23/1987
• Issued: 01/17/1989
• Est. Priority Date: 03/13/1986
• Status: Expired due to Term

• Current Assignee: Drexelbrook Controls, Inc.
• Original Assignee: Drexelbrook Controls, Inc.
• Inventors: Petersen, Steven R., Kramer, L. Jonathan
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Mattson, Brian M.
• Application Number:
  US07/113,358
• Time in Patent Office: 452 Days
• Field of Search: 364/481, 364/508, 364/509, 364/550, 364/551, 340/870.16, 340/601, 340/603, 324/57 R, 324/60 R, 324/60 C, 324/58.5 R, 73/1 H, 73/304 C
• US Class Current: 702/33
• CPC Class Codes: G01F 23/261 for discrete levels
• CPC Class Codes: G01F 23/265 for discrete levels
• CPC Class Codes: G01F 23/266 measuring circuits therefor
• CPC Class Codes: G01F 23/802 Particular electronic circuits for digital processing equipment

Abstract

A multiple set point material condition monitoring system includes a material responsive sensor developing a material condition dependent admittance and a reference admittance generator, generating a plurality of different admittance values in a predetermined sequence repeatedly during operation of the system. The circuitry coupled with the sensor and the reference admittance generator outputs a signal which is a function both of the material condition generated admittance and each of the plurality of reference admittance values, in sequence. Storage means are provided for storing a characteristic of the output signal for feedback to the circuitry when that particular reference admittance value for generating that output signal is again generated by the reference admittance generator. Preferably, the sensor and reference admittance generator are coupled across each of a pair of arms of bridge network which constitutes part of the circuitry developing the output signal.

Claims

1. A system for monitoring a specified condition of materials at multiple set points comprising:

comparison means having a pair of inputs;

material sensing means comprising a single admittance probe coupled to one of the inputs of the comparison means for providing an admittance indicative of the condition of the materials;

sequential admittance generator means coupled to the other input of the comparison means for automatically and repeatedly providing a plurality of different admittance values, each admittance value corresponding to a different set point;

detector means coupled to the comparison means for detecting a difference between the admittance provided by the material sensing means and each of the admittances provided by the sequential admittance generator and providing an output indicative thereof;

storage means coupled to the detector means for storing indications of differences detected by the comparison means for each admittance value provided by the sequential admittance generator means;

output means coupled to the storage means for providing a plurality of output signals, each output signal corresponding to at least one of the indications stored by the storage means;

whereby each output signal represents a relationship between at least one of the multiple set points and the condition of the materials indicated by the material sensing means.

2. System according to claim 1 wherein the comparison means comprises a bridge network having a pair of arms representing the inputs of the comparison means, the detector means detecting an imbalance condition in the bridge network for each admittance value provided by the sequential admittance generator.

3. System according to claim 2 wherein the output provided by the detector means is indicative of at least one degree, phase and direction of imbalance in the bridge network.

4. System according to claim 2 further comprising means coupled to the bridge network for energizing the bridge network by applying an alternating signal thereto.

5. System according to claim 2 further comprising feedback means coupled between the storage means and the detector means, the feedback means providing to the detector means, for each admittance value provided by the sequential generator means, an indication of the imbalance condition of the bridge network when the corresponding admittance value was last provided.

6. System according to claim 5 wherein the feedback means introduces controlled hysteresis into the detector means.

7. System according to claim 5 wherein the feedback means prevents interaction between successive set points.

8. System according to claim 2 wherein the sequential admittance generator means comprises:

a plurality of capacitors; and

,

means coupled to the plurality of capacitors for selecting a sequence thereof.

9. System according to claim 8 wherein the means coupled to the plurality of capacitors comprises:

a clock;

a counter coupled to and sequenced by the clock;

an address generator coupled to the counter for providing addresses in response to outputs provided by the counter;

a decoder circuit coupled to the address generator for decoding the addresses;

switch means coupled to the decoder means for selectively coupling the capacitors to one of the pair of arms of the bridge network.

10. System according to claim 2 wherein the detector means comprises an error amplifier.

11. System according to claim 10 wherein the detector means further comprises a demodulator coupled to the error amplifier.

12. System according to claim 11 further comprising an output amplifier coupled to the demodulator for providing bi-level signals indicative of the direction of imbalance of the bridge network.

13. System according to claim 12 wherein the storage means comprises:

latch means having a plurality of stages for storing each of the bi-level signals provided by the output amplifier; and

,

multiplexer means coupled to the latch means and to the address generator for selecting one of the signals stored in the latch means for feedback to the demodulator.

14. System according to claim 13 wherein the output means is coupled to the latch means and each output signal is derived from a different stage of the latch means.

15. Apparatus comprising:

(a) an admittance probe;

(b) a bridge network having a pair of arms, the admittance probe being coupled to one of the arms;

(c) sequential admittance generator means coupled to the other arm of the bridge network for automatically and repeatedly providing, in sequence, a plurality of admittances, each representing a set point for comparison with an admittance provided by the probe;

(d) oscillator means coupled to and energizing the bridge network;

(e) detection means coupled to the bridge network for providing an indication of at least one of degree, phase and direction of imbalance in the bridge network for each admittance provided by the sequential admittance generator means;

(f) storage means coupled to the detection means for storing an indication of at least the direction of imbalance of the bridge network for each admittance provided by the sequential admittance generator means;

(g) feedback means coupled between the storage means and the detector means for providing to the detector means, for each admittance value provided by the sequential admittance generator means, the indication of imbalance of the bridge network stored by the storage means for the corresponding admittance last provided by the sequential generator admittance means; and

,

(h) output means coupled to the storage means for providing a plurality of output signals, each output signal corresponding to at least one of the indications stored by the storage means.

16. Apparatus according to claim 15 wherein the detector means comprises a demodulator and the feedback means introduces controlled hysteresis into the demodulator, the feedback means preventing interaction between successive set points.

17. Apparatus according to claim 15 wherein the sequential admittance generator means comprises:

a plurality of capacitors; and

,

means coupled to the plurality of capacitors for selectively coupling one or more thereof to the bridge network.

18. Apparatus according to claim 17 wherein the means coupled to the plurality of capacitors comprises:

clock means;

counter means coupled to and sequenced by the clock means;

address generator means coupled to the counter means for providing addresses in response to outputs from the counter means;

decoder means coupled to the address generator means for decoding the addresses; and

,

switch means coupled to the decoder means and to the plurality of capacitors for coupling the capacitors to the bridge network in response to outputs from the decoder means.

19. Apparatus according to claim 15 wherein the storage means comprises:

plural stage latch means receiving the indications from the detection means and storing the indication corresponding to each admittance provided by the sequential admittance generator means in a different stage; and

,

multiplexer means coupled to the latch means and to an address generator associated with the sequential admittance generator means for selecting one of the indications stored in the latch means for feedback to the detector means.

20. Apparatus according to claim 19 wherein the indications received by and stored in the latch means are bi-level signals indicative of the direction of imbalance of the bridge network.

21. Apparatus according to claim 19 wherein the output means is coupled to the latch means and each output signal is derived from a different stage of the latch means.

22. Apparatus for monitoring a specified condition of materials at multiple set points comprising:

(a) material sensing means comprising only a single admittance probe for providing an admittance related to a condition of materials desired to be monitored;

(b) a bridge network having a pair of arms, the material sensing means being coupled to one of the arms;

(c) sequential admittance generator means coupled to the other arm of the bridge network for automatically and cyclically providing a plurality of admittances each representing a set point for comparison with the condition of materials monitored, the sequential admittance generator means comprising a plurality of capacitors and means coupled to the plurality of capacitors for selectively coupling one or more thereof to the bridge network;

(d) an error amplifier coupled to the bridge network and a demodulator coupled to the error amplifier for providing an indication of at least one of degree, phase and direction of imbalance of the bridge network;

(e) an output amplifier coupled to the demodulator for providing a bi-level signal indicative of at least the direction of imbalance of the bridge network;

(f) storage means comprising a plural stage latch coupled to the output amplifier for storing, for each admittance provided by the sequential admittance generator means, the bi-level signal provided by the output amplifier;

(g) multiplexer means coupled to the storage means, to the means coupled to the plurality of capacitors, and to the demodulator for selecting, for each admittance provided by the sequential admittance generator means, the bi-level signal stored in the storage means for the corresponding admittance last provided by the sequential admittance generator means for feedback to the demodulator;

(h) output means coupled to the storage means for providing a plurality of output signals, each output signal being derived from at least one of the stages of the latch and representing a relationship between at least one of the set points and the condition of materials monitored.

23. Method of monitoring a specified condition of materials comprising the steps of:

(a) providing an admittance related to the condition of materials monitored;

(b) automatically and cyclically comparing a plurality of reference admittances to the admittance provided in step (a), each reference admittance corresponding to one of a plurality of set points;

(c) detecting a difference between each reference admittance and the admittance provided in step (a) and providing an indication of each difference;

(d) storing each indication provided in step (c);

(e) providing a plurality of output signals each corresponding to at least one of the stored indications, each output signal representing a relationship between the monitored condition and at least one of the set points.

24. Method according to claim 23 wherein step (c) includes introducing controlled hysteresis by feeding back, for each reference admittance provided in step (b), the indication stored for the corresponding reference admittance last provided in step (b).