Process variable transmitter having a non-interacting operating range adjustment

• US 4,494,183 A
• Filed: 06/17/1982
• Issued: 01/15/1985
• Est. Priority Date: 06/17/1982
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Olsen, Arthur M., Bayer, Stephen J.
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US06/389,633
• Time in Patent Office: 943 Days
• Field of Search: 364/153, 364/154, 364/185, 364/550, 364/551, 364/571, 364/573, 364/570, 364/579, 364/582, 73/1 R, 324/74, 324/115, 324/116, 324/130, 324/99 R, 324/99 D
• US Class Current: 700/34
• CPC Class Codes: G01D 18/008 with calibration coefficients stored in memory
• CPC Class Codes: G01D 3/022 having an ideal characteristic, map or correction data stored in a digital memory
• CPC Class Codes: G01L 27/002 Calibrating, i.e. establishing true relation between transducer output value and value to be measured, zeroing, linearising or span error determination
• CPC Class Codes: G01R 15/08 Circuits for altering the measuring range
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

The operating range for a process variable transmitter used as a pressure transmitter is selectively non-interactively adjusted by successively applying upper and lower range values (URV and LRV) of input pressure to produce an LRV output signal and calculating the URV and the Span which is equal to the difference between the upper and lower range values, i.e., URV-LRV, to produce outputs from the transmitter representing the new upper and lower range values corresponding to the calculated Span.

Claims

1. A process variable transmitter comprising

a process variable input for connection to a source of a signal representative of a process variable,

a computing means connected to said input for producing a transmitter output representing a desired lower range value of said process variable and a desired upper range value of said process variable,

a set-lower-range value control means for controlling said computing means to produce a lower range value transmitter output at a first value of said process variable and

a set-upper-range value control means for controlling said computing means to produce an upper range value transmitter output at a second value of said process variable by calculating the difference between the upper-range value and the lower-range value.

2. A process variable transmitter as set forth in claim 1 wherein said computing means incudes a digital microprocessor and a digital-to-analog converter to convert an output from said microprocessor to a representative current as said transmitter output.

3. A process variable transmitter as set forth in claim 2 wherein said microprocessor computes an upper range value and a span between said lower range value and said upper range value according to:

space="preserve" listing-type="equation">Output=DAC.0.+(((Input-LRV)*(URL/Span))/URL)*DACSPAN

where;

5. A process variable transmitter as set forth in claim 1 wherein said first transmitter output is 4 ma. and said second transmitter output is 20 ma.

7. A method of changing the range as set forth in claim 5 wherein said computing means uses the following equation for calculating the difference:

space="preserve" listing-type="equation">Output=DAC.0.+(((Input-LRV)*(URL/Span))/URL)*DACSPAN

where;

4. DAC.0. is the output of said digital-to-analog converter to produce said first transmitter output,

URL is the upper range limit of the transmitter output,

LRV is the lower range value of the transmitter output,

Span=URV-LRV, where URV is the upper range value of the transmitter output, and

DACSPAN is the additional input to the DAC which produces said second transmitter output.

6. A method of changing the range of a process variable transmitter having a computing means for computing a transmitter output signal including the steps of applying a first predetermined process variable input to said computing means, applying a first control signal to said computing means to produce a first transmitter output signal as a lower range value, applying a second process variable input to said computing means, and applying a second control signal to said computing means to produce a second transmitter output signal as an upper range value by calculating the difference between the lower and upper range values.

9. A method as set forth in claim 6 wherein URV is greater than LRV.

10. A method as set forth in claim 6 wherein URV is less than LRV.

8. DAC.0. is the output of said digital-to-analog converter to produce said first transmitter output,

URL is the upper range limit of the transmitter output,

LRV is the lower range value of the transmitter output,

Span=URV-LRV, where URV is the upper range value of the transmitter output, and

DACSPAN is the additional output to the DAC which produces said second transmitter output signal.