Multiple calibration ranges stored in a process transmitter
Process variable transmitters, and method for calibrating such device, are disclosed that support calibrating, within a single transmitter device, multiple operating ranges such that a transmitter can switch from a first calibration correction definition associated with a first calibrated range, to a second calibration correction definition associated with a second calibrated range without having to perform a calibration procedure. Thus, rather than supporting only a single calibration definition, a calibration memory for the process variable transmitter comprises multiple calibration correction definition entries. Each calibration correction definition entry potentially expresses a correction relationship for one of multiple calibrated ranges represented in the calibration memory.
1 . A process variable transmitter comprising:
a process variable sensor;
a processing unit, adapted to receive a value corresponding to a signal received from the process variable sensor, the processing unit including output value computation stages for rendering a calibrated output value based upon the received value including:
a characterization computation stage, and
a calibration computation stage that is distinct from the characterization stage; and
a calibration memory comprising multiple calibration correction definition entries expressing a correction relation for generating calibration corrections for multiple calibrated ranges within an operating range of the process variable transmitter.
2 . The process variable transmitter of claim 1 wherein a calibration correction definition entry corresponds to a pair of calibration points delimiting one of the multiple calibrated ranges.
3 . The process variable transmitter of claim 2 wherein each calibration correction definition entry includes a slope and offset value for a linear correction equation associated with one of the multiple calibrated ranges.
4 . The process variable transmitter of claim 2 wherein a calibration correction definition entry further corresponds to a sensor vicinity temperature at which calibration information was obtained for the calibration correction definition entry.
5 . The process variable transmitter of claim 4 wherein the calibration computation stage applies a calibration correction equation based upon at least one calibration correction definition entry selected according to a sensor vicinity temperature.
6 . The process variable transmitter of claim 5 wherein the calibration correction equation is derived from two calibration correction definitions associated with two differing sensor vicinity temperatures.
7 . The process variable transmitter of claim 1 wherein the correction definition is specified, at least in part, as a percentage of a specified upper range limit for the process variable transmitter.
8 . The process variable transmitter of claim 1 wherein a calibration correction definition entry specifies a higher order correction curve for a calibrated range.
9 . The process variable transmitter of claim 1 wherein a set of calibration relations are specified for a series of adjacent ranges, and wherein calibration values are generated such that calibrated output values are equal at boundaries between adjacent calibrated ranges.
10 . The process variable transmitter of claim 9 wherein the ranges are specified as a percentage of a specified upper range limit for the process variable transmitter.
11 . The process variable transmitter of claim 9 wherein the processing unit dynamically changes between ones of the set of calibration relations in accordance with changes to a sensed process variable input value.
12 . The process variable transmitter of claim 1 wherein the calibration memory comprises a first calibration table comprising a default set of calibration correction definition entries and a second calibration table comprising a user-specified set of calibration correction definition entries.
13 . The process variable transmitter of claim 12 wherein the user-specified set of calibration correction definition entries is generated by a combination of user calibration points and calibration points provided by the first calibration table.
14 . A method of enabling a process variable transmitter to apply calibration-based corrections to calculated sensor measurements in the process variable transmitter including a non-volatile memory configured to store multiple calibration-based correction definitions corresponding to sub-ranges within a full operating range of the process variable transmitter, the method comprising for each of at least two calibrated ranges the following:
taking sensor readings for at least two known process variable inputs corresponding to a calibrated range;
generating, for the two known process variable inputs, digital non-calibrated sensor reading values;
applying values of the two known process variable inputs to the non-calibrated sensor reading values to render a calibration correction definition; and
storing the calibration correction definition in an entry, of a calibration memory structure supporting simultaneously storing multiple calibration correction definitions associated with particular calibrated ranges, corresponding to the calibrated range within the non-volatile memory, wherein the process variable transmitter includes a processing unit that is adapted to receive a value corresponding to a sensor reading of the process variable transmitter and utilizes one of the multiple calibration correction definitions to generate a corresponding calibrated output value, and wherein the processing unit includes:
a characterization computation stage, and
a calibration computation stage that is distinct from the characterization stage.
15 . The method of claim 14 wherein the calibration correction definition corresponds to a pair of calibration points for a calibrated range.
16 . The method of claim 15 wherein the calibration definition comprises a linear correction equation, and wherein the applying step comprises:
determining a calibration offset and a calibration slope for the calibration correction definition.
17 . The method of claim 15 wherein the calibration correction definition further corresponds to a sensor vicinity temperature at which calibration information was obtained for the calibration correction definition.
18 . The method of claim 17 further comprising generating calibration corrections for at least two temperatures for a calibrated range to facilitate applying a calibration correction equation based upon at least one calibration correction definition entry selected according to a sensor vicinity temperature.
19 . The method of claim 14 wherein the calibration correction definition is specified, at least in part, as a percentage of a specified upper range limit for the process variable transmitter.
20 . The method of claim 14 wherein the taking sensor reading step comprises taking readings for at least three distinct known process variable inputs, and wherein the calibration correction definition specifies a non-linear correction curve for a calibrated range.
21 . The method of claim 14 wherein the at least two calibrated ranges comprise a series of adjacent ranges, and wherein calibration correction definition values are generated such that calibrated output values are equal at boundaries between adjacent calibrated ranges.
22 . The method of claim 21 wherein the ranges are specified as a percentage of a specified upper range limit for the process variable transmitter.