Fast technique for converting sampled analog measurements of a physical quanity to values expressed in engineering unit format

• US 5,748,105 A
• Filed: 09/09/1996
• Issued: 05/05/1998
• Est. Priority Date: 11/15/1991
• Status: Expired due to Fees

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Kelly, Christopher P. J.
• Primary Examiner(s): Hofsass, Jeffrey
• Assistant Examiner(s): HILL, ANDREW M
• Application Number:
  US08/709,594
• Time in Patent Office: 603 Days
• Field of Search: 340/870.21, 340/870.05, 340/870.17, 364/571.02, 364/571.04, 364/571.05, 364/571.07, 364/573, 364/577, 364/581, 364/553, 364/554, 364/723, 341/106, 341/165
• US Class Current: 340/870.21
• CPC Class Codes: G01D 3/022 having an ideal characteristic, map or correction data stored in a digital memory
• CPC Class Codes: G01D 3/0365 the undesired influence being measured using a separate sensor, which produces an influence related signal
• CPC Class Codes: G01K 1/028 arrangements for numerical indication
• CPC Class Codes: G01K 2219/00 Thermometers with dedicated analog to digital converters

Abstract

An engineering unit converter system for converting an analog measurement into an engineering value. An analog measurement of a physical quantity is transformed into a digital value. The digital value is then split into a high order digit and a lower order digit. The high order digit is used as an address to a memory device for fetching a line segment coefficient and a line segment offset coefficient. The lower order digit is multiplied with the line segment coefficient in a multiplier resulting in a product. The product is added to the line segment coefficient offset resulting in a sum whose value is an engineering unit. One embodiment is directed to converting temperature measurements into engineering units via thermocouples. This embodiment includes: thermocouple devices, resistance thermal devices or positive temperature coefficient thermistors, adders, multipliers, and memory devices (readable and writable memory devices).

Claims

1. A method for converting an analog voltage value representing a physical quantity being measured, to a value expressed in an engineering unit format, the method comprising the steps of:

storing in a memory a value representing a line segment slope coefficient and a value representing a line segment offset coefficient, wherein said line segment slope coefficient and said line segment offset coefficient are pre-scaled by a predetermined scale factor prior to being stored in said memory;

converting the analog voltage value into a digital value;

separating said digital value into a predetermined number of high order bits and a predetermined number of low order bits, wherein said high order bits and said low order bits together comprise a total number of bits of said digital value, and wherein said high order bits act as an addressing means for fetching said line segment slope coefficient and line segment offset coefficient from said memory;

multiplying said low order bits with said line segment slope coefficient to generate a value representing a product of the multiplication;

adding said product and said line segment offset coefficient fetched from said memory to generate a value representing a sum, said sum being the value expressed in the engineering unit format; and

re-scaling said sum by said predetermined scale factor to correct for pre-scaling.

2. The method of claim 1, wherein said step of resealing is performed in a barrel shifter.

3. The method of claim 1, wherein the steps of multiplying and adding are performed in integer devices.

4. The method of claim 1, wherein said line segment slope coefficient represents a slope of a segment of a conversion curve describing the relationship between said analog voltage representing the physical quantity being measured and the value expressed in engineering unit format;

and

said line segment offset coefficient represents an offset coefficient, which is equal to a base corresponding to a segment of the conversion curve.

5. A method for converting an analog voltage value representing a physical quantity being measured, to a value expressed in an engineering unit format, the method comprising the steps of:

storing in a memory a value representing a line segment slope coefficient and a value representing a line segment offset coefficient, wherein said line segment slope coefficient and said line segment offset coefficient are pre-scaled by a predetermined scale factor prior to being stored in said memory, said line segment slope coefficient represents a slope of a segment of a conversion curve describing the relationship between said analog voltage representing the physical quantity being measured and the value expressed in engineering unit format, said line segment offset coefficient represents an offset coefficient, which is equal to a base corresponding to a segment of the conversion curve;

converting the analog voltage value into a digital value;

separating said digital value into a predetermined number of high order bits and a predetermined number of low order bits, wherein said high order bits and said low order bits together comprise a total number of bits of said digital value, and wherein said high order bits act as an addressing means for fetching said line segment slope coefficient and line segment offset coefficient from said memory;

multiplying in an integer device said low order bits with said line segment slope coefficient to generate a value representing a product of the multiplication;

adding in an integer device said product and said line segment offset coefficient fetched from said memory device to generate a value representing a sum, said sum being a value expressed in engineering unit format; and

re-scaling using a barrel shifter said sum by said predetermined scale factor to correct for pre-scaling.