System and method for linearizing analog measurements during analog-to-digital conversion

• US 3,979,745 A
• Filed: 02/22/1974
• Issued: 09/07/1976
• Est. Priority Date: 02/22/1974
• Status: Expired due to Term

• Current Assignee: Westronics, Inc. (Thermo Fisher Scientific Incorporated)
• Original Assignee: Westronics, Inc. (Thermo Fisher Scientific Incorporated)
• Inventors: Bishop, Allen J.
• Primary Examiner(s): Sloyan, Thomas J.
• Application Number:
  US05/444,953
• Time in Patent Office: 928 Days
• Field of Search: 340/347 NT, 340/347 AD, 179/15 AV, 235/197, 235/194, 73/341, 73/1 F
• US Class Current: 341/140
• CPC Class Codes: G01D 3/022 having an ideal characteristic, map or correction data stored in a digital memory
• CPC Class Codes: G01K 7/14 Arrangements for modifying the output characteristic, e.g. linearising
• CPC Class Codes: H03M 1/52 Input signal integrated with linear return to datum
• CPC Class Codes: H03M 1/60 with intermediate conversion to frequency of pulses

Abstract

An instrument for linearizing a non-linear analog output produced from a sensor such as a thermocouple to obtain a true measurement of the parameter or engineering units of interests. The full range of the non-linear analog output is divided into segments and within each segment the second slope or the rate of change of the first slope of the analog output is predetermined and stored. In carrying out measurements, the magnitude of the analog output sensed is converted to constant frequency pulses. When measurements are carried out, within a given segment the corresponding second slope data is employed to modify the frequency of the constant frequency pulses to obtain output pulses for accumulation. These output pulses have a frequency which at any given moment is representative of the first slope of the analog output and which changes at a rate representative of the rate of change of the first slope of the analog output. The resulting output pulses thus are accumulated at a non-linear rate to obtain an output that will accurately follow the non-linear curve of the sensor and which will result in a true measurement of the engineering units of interest.

Claims

1. Apparatus for producing an accurate measurement of the engineering units of interest represented by the output signal of an analog transducer having a non-linear output function, comprising:

an analog-to-digital converter for producing a digital output comprising a quantity of constant frequency pulses representative of the magnitude of the output signal of said analog transducer,

storage means for storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

means responsive to said constant frequency pulses and responsive to said data functions stored for converting said constant frequency pulses to output pulses whose frequency changes linearly within each segment at a rate dependent upon the corresponding data function, and

means for accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

2. Apparatus for producing an accurate measurement of the engineering units of interest represented by the output signal of an analog transducer having a non-linear output function, comprising:

an analog-to-digital converter for converting the magnitude of the output signal of said analog transducer to a time period representative of said magnitude and for producing during same time period a digital output comprising a quantity of constant frequency pulses representative of the magnitude of the output signal of said analog transducer,

storage means for storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

means responsive to said constant frequency pulses produced and sequentially responsive to said data functions stored for producing second pulses at a frequency which is a function of the rate of change of the slope of the non-linear output function of said transducer within said segments of the non-linear output function of said analog transducer,

means responsive to said constant frequency pulses and to said second pulses for producing output pulses at a frequency which changes linearly within each segment at a rate dependent upon the corresponding data function, and

means for accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

3. Apparatus for producing an accurate measurement of the engineering units of interest represented by the output signal of an analog transducer having a non-linear output function, comprising:

an analog-to-digital converter for converting the magnitude of the output signal of said analog transducer to a time period representative of said magnitude and for producing during said time period a digital output comprising a quantity of constant frequency pulses representative of the magnitude of said output signal of said analog transducer,

storage means for storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

first conversion means responsive to said constant frequency pulses and sequentially responsive to selected ones of said data functions stored for producing second pulses at a frequency which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within said segments corresponding to said selected data functions,

counter means responsive to said second pulses for producing a binary output which is a function of the slope of the non-linear output function of said analog transducer within said segments corresponding with said selected data functions and which changes at a rate which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within said segments corresponding with said selected data functions,

second conversion means responsive to said constant frequency pulses and to said changing binary output for producing output pulses at a frequency which changes linearly within each segment at a rate dependent upon the corresponding data function, and

means for accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

4. The apparatus of claim 3 wherein said first and second conversion means comprise binary rate multipliers each of which is capable of producing an output frequency f_out having the following relationship:

##EQU3## wherein;

f_in is the frequency of input pulses,

M is a rate input which is a binary number, and

K is a constant.

5. In a system including an analog-to-digital converter, storage means for storing a plurality of data functions each of which is a function of the rate of change of the slope of the non-linear output function of an analog transducer within a different segment of a given range of the non-linear output function of said analog transducer, linearizing means, and accumulating means, the method of producing an accurate measurement of the engineering units of interest represented by the output signal of said analog transducer having a non-linear output function, comprising the steps of:

operating said analog-to-digital converter to produce a digital output comprising a quantity of constant frequency pulses representative of the magnitude of said output signal of said analog transducer,

storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

in response to said constant frequency pulses produced and sequentially responsive to said data functions stored, converting said constant frequency pulses to output pulses whose frequency changes linearly within each segment at a rate dependent upon the corresponding data function, and

accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

6. In a system including an analog-to-digital converter, storage means for storing a plurality of data functions each of which is a function of the rate of change of the slope of the non-linear output function of an analog transducer within a different segment of a given range of the non-linear output function of said analog transducer, linearizing means, and accumulating means, the method of producing an accurate measurement of the engineering units of interest represented by the output signal of said analog transducer having a non-linear output function, comprising the steps of:

operating said analog-to-digital converter to convert the magnitude of the output signal of said analog transducer to a time period representative of said magnitude and producing during said time period a digital output comprising a quantity of constant frequency pulses representative of the magnitude of said output signal of said analog transducer,

storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

in response to said constant frequency pulses produced and sequentially responsive to said data functions stored, producing second pulses at a frequency which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within said segments of the non-linear output function of said analog transducer,

in response to said constant frequency pulses and to said second pulses, producing output pulses at a frequency which changes linearly within each segment at a rate dependent upon the corresponding data function, and

accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

7. In a system including an analog-to-digital converter, storage means for storing a plurality of data functions each of which is a function of the rate of change of the slope of the non-linear output function of an analog transducer within a different segment of a given range of the non-linear output function of said analog transducer, linearizing means, and accumulating means, the method of producing an accurate measurement of the engineering units of interest represented by the output signal of said analog transducer having a non-linear output function, comprising the steps of:

operating said analog-to-digital converter to convert the magnitude of the output signal of said analog transducer to a time period representative of said magnitude and producing during said time period a digital output comprising a quantity of constant frequency pulses representative of the magnitude of said output signal of said analog transducer,

storing a plurality of data functions, each of which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within a different segment of a given range of the non-linear output function of said analog transducer,

in response to said constant frequency pulses and sequentially responsive to selected ones of said data functions stored, producing second pulses at a frequency which is a function of the rate of change of the slope of the non-linear output function of said analog transducer within said segments corresponding with said selected data functions,

in response to said second pulses, producing a binary output which is a function of the slope of the non-linear output function of said analog transducer within said segments corresponding with said selected data functions and which changes at a rate which is a function of the rate of change of the slope of said non-linear output function of said analog transducer within said segments corresponding with said selected data functions,

in response to said constant frequency pulses and to said changing binary output, producing output pulses at a frequency which changes linearly within each segment at a rate dependent upon the corresponding data function, and

during said time period, accumulating said output pulses for the production of an accurate measurement of the engineering units of interest represented by the analog transducer output signal.

8. Apparatus for producing an accurate measurement of the engineering units of interest represented by the output signal of an analog transducer having a non-linear output function comprising:

an analog-to-digital converter for converting the magnitude of the output signal of said analog transducer to a time period representative of said magnitude and for producing during said time period a digital output comprising a quantity of constant frequency pulses representative of the magnitude of said output signal of said analog transducer,

storage means for storing a plurality of binary functions each of which is a function of the rate of change of the slope of the output function of said analog transducer within a different segment of a given range of the output function of said analog transducer,

first and second conversion means each having a first input for receiving a digital input signal, a second input for receiving a binary rate input signal, and an output for producing a digital output whose frequency is proportional to the product of the frequency of the digital input signal and the binary rate input signal,

binary counter means having input means for receiving a digital signal and an output for producing a binary output which is a function of the sum of the digital counts applied to its input means,

means for loading the initial slope of said output function of said analog transducer into said binary counter,

means for applying the digital output of said analog-to-digital converter to said first inputs of said first and second conversion means,

means for sequentially applying said binary functions stored in said storage means to said second input of said first conversion means,

means for applying a digital signal representative of the digital output of said first conversion means to said input means of said binary counter means,

means for applying the binary output of said counter means to said second input of said second conversion means for the production of a digital output comprising output pulses produced at a frequency which changes linearly within each segment at a rate dependent upon the corresponding binary function applied to the second input of said first conversion means,

accumulating means for accumulating the digital output of said second conversion means, and

display means for displaying the counts accumulated in said accumulator for the production of an accurate measurement of the engineering units of interest represented by the output signal of said analog transducer.