Apparatus and method for detecting when a measured variable represented by a string of digital pulses reaches a plateau

• US 4,041,404 A
• Filed: 06/01/1976
• Issued: 08/09/1977
• Est. Priority Date: 06/01/1976
• Status: Expired due to Term

• Current Assignee: Leeds & Northrup Co.
• Original Assignee: Leeds & Northrup Co.
• Inventors: Lewis, Ronald Cyril Jr.
• Primary Examiner(s): Zazworsky, John
• Application Number:
  US05/691,687
• Time in Patent Office: 434 Days
• Field of Search: 328/44, 328/114-116, 328/132, 328/135, 328/130, 328/150, 307/235 R, 307/235 A, 307/235 J, 324/99 D, 324/111, 340/347 NT
• US Class Current: 377/19
• CPC Class Codes: G01K 1/028 arrangements for numerical indication
• CPC Class Codes: G01K 3/10 in respect of time, e.g. reacting only to a quick change of temperature
• CPC Class Codes: G01K 7/025 expendable thermocouples
• CPC Class Codes: H03K 5/153 Arrangements in which a pulse is delivered at the instant when a predetermined characteristic of an input signal is present or at a fixed time interval after this instant switching at zero crossing H03K17/13

Abstract

A method for detecting a plateau for a measured variable by comparing the clock pulses from a dual slope analog to digital converter which are counted during consecutive pairs of conversions. The counter is decremented during the first conversion and incremented during the second. If the counts are detected as being identical within a prescribed number of counts an accumulator is incremented. A predetermined number of successive increments of the accumulator indicates a plateau. The accumulator is cleared whenever the counts of a pair of conversions are not within the window.

Claims

1. Apparatus for detecting when the value of a measured variable has reached a plateau when that value is represented by periodically produced strings of pulses having pulse counts representative of the value, comprising;

a first counting means operable to count consecutive pairs of said pulse strings so that the consecutive counts are in opposite directions,

a second counting means, and

means responsive to the output of said first counting means at the end of each pair of pulse strings and operable to increment said second counting means when the count accumulated by said first counting means at the end of the second string of said pair is within a predetermined number of counts of the count existing before counting the first string of the pair and to clear said second counting means when the count is not within the predetermined number, whereby the accumulation of a predetermined number of counts in said second counter is indicative of said measured variable reaching a plateau.

2. Apparatus as set forth in claim 1 in which said first counter is operative to count down when counting the first pulse string of each pair.

3. Apparatus as set forth in claim 1 in which said first counting means includes means for setting said predetermined number of counts by which the first pulse string can differ from said second pulse string before said first counter fails to increment said second counter.

4. A method for detecting when the value of a measured variable has reached a plateau when that value is represented by periodically produced strings of pulses having pulse counts representative of the value, comprising the steps of

counting consecutive pulse trains in opposite directions,

producing a signal at the end of the second pulse train of each pair of pulse trains when the count of the second pulse train is within a predetermined number of counts with respect to the count of the first pulse train of the pair,

counting the number of consecutive signals produced, and

indicating a plateau has been reached when the count of the number of consecutive signals reaches a predetermined value.

5. Apparatus for detecting when the value of a variable supplied as an input to a dual slope analog-to-digital converter is at a plateau value, comprising;

a first counting means operable to count the clock pulses over the full conversion cycle of the converter,

means for clearing said first counter in response to alternate strobe pulses from said analog-to-digital converter,

means for operating said first counter to count UP until the variable supplied reaches a minimum value after which the direction of count is alternated such that over separate pairs of conversions a DOWN count of the clock pulses precedes an UP count of those pulses,

a second counter,

means responsive to a roll-over of said first counter at the end of a pair of conversions to increment the second counter and responsive to an overflow or underflow of said first counter with respect to roll-over beyond a preset number of pulses to reset said second counter,

means responsive to a full count on said second counter to indicate a plateau has been reached by said value.

6. a digital plateau detecting device for use with an analog to digital converter having a conversion period and producing in each of said conversion periods a pulse train representative of the value of a measured variable with successive pulse being representative of successive values of said measured variable, comprising;

a bidirectional pulse counter which counts the pulses of said pulse train and is cleared at the beginning of each conversion period,

means for controlling said bidirectional counter to count the pulses during the first of each consecutive pair of conversions in one direction starting from a clear state and for counting the pulses during a second conversion in the other direction starting from the state of the counter existing after the count from the first conversion,

a flip-flop,

means responsive to the state of said counter after the second of each consecutive pair of conversions when said counter has returned to the state within a predetermined count of the state existing prior to said first count for producing a set signal,

means responsive to the state of said counter after said second conversion when said counter has been returned to a state indicating at least a predetermined inequality between the count during said first conversion and the count during said second conversion for producing a reset signal to said flip-flop, and

a counter connected to the output of said flip-flop and operative to be incremented in response to each of said set signals and to be cleared in response to each of said reset signals, whereby the accumulation of a predetermined count indicates a plateau.