Method of digital process variable transmitter calibration and a process variable transmitter system utilizing the same
First Claim
1. A method for digital calibration of a process variable sensor comprising the steps ofstoring a characterization equation in the form of PV=A0 A1 P+A2 P2 + . . . +Ai Pi where Ai =f (S,T) and PV is the process variable, P is the output of a process variable differential value measuring sensor, S is the output of a process variable static value measuring sensor and T is the output of a sensor measuring an environmental temperature affecting the outputs of the process variable measuring sensors and where ##EQU2## measuring a process variable by the process variable sensor to produce an analog output signal representative of the process variable,converting the output from the process variable sensor to a digital representation thereof andsupplying the digital representation to a digital computer to be used in computing a digital output in accordance with the stored characterization equation to produce a corrected version of the output of the process variable sensor independent of the effects of the environmental conditions.
0 Assignments
0 Petitions
Accused Products
Abstract
A method of digital process variable transmitter calibration includes the steps of sensing the process variable (PV) to produce an analog output which is converted to a digital signal representation. The digital signal is corrected by a microprocessor using a characterization equation previously individually developed during a manufacturing testing of the process variable transmitter over a predetermined range of environmental stimuli to ascrtain the coefficients for a polynomial in the form of PV=Ao =A1 P+A2 +. . . Ai Pi. Thus, the digital computer produces a process variable representation as a modified digital output. Subsequently, the digital output from the computer is converted to a conventional 4-20 mA analog signal for use as a process control signal. The process variable transmitter apparatus utilizing the aforesaid method includes means for receiving an output from a process variable sensor, an analog-to-digital converter for converting the received output from the sensor to a digital representation, a digital computer, a non-volatile memory for storing an individualized correction equation determined during the manufacturing testing of the transmitter and a digital-to-analog converter for converting the computer output to an analog control signal.
-
Citations
13 Claims
-
1. A method for digital calibration of a process variable sensor comprising the steps of
storing a characterization equation in the form of PV=A0 A1 P+A2 P2 + . . . +Ai Pi where Ai =f (S,T) and PV is the process variable, P is the output of a process variable differential value measuring sensor, S is the output of a process variable static value measuring sensor and T is the output of a sensor measuring an environmental temperature affecting the outputs of the process variable measuring sensors and where ##EQU2## measuring a process variable by the process variable sensor to produce an analog output signal representative of the process variable, converting the output from the process variable sensor to a digital representation thereof and supplying the digital representation to a digital computer to be used in computing a digital output in accordance with the stored characterization equation to produce a corrected version of the output of the process variable sensor independent of the effects of the environmental conditions.
-
7. A process variable transmitter apparatus comprising
analog-to-digital converter means for converting an analog output from a process variable sensor into a digital representation thereof, a non-volatile memory means for storing a transmitter characterization equation in the form of PV=A0 A1 P+A2 P2 + . . . +Ai Pi where Ai =f (S,T) and PV is the process variable, P is the output of a process variable differential value measuring sensor, S is the output of a process variable static value measuring sensor and T is the output of a sensor measuring an environmental temperature affecting the outputs of ther process variable measuring sensors and where ##EQU3## a digital computer means connected to said converter means and said memory means for computing a digital output in accordance with the stored transmitter characterization equation to produce a corrected version of the digital representation from said converter means independent of the effects of the environment conditions.
Specification