Digital transmitter with variable resolution as a function of speed

• US 4,866,435 A
• Filed: 10/16/1987
• Issued: 09/12/1989
• Est. Priority Date: 10/16/1987
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Frick, Roger L.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Queen, Tyrone
• Application Number:
  US07/109,490
• Time in Patent Office: 697 Days
• Field of Search: 340/870.07, 340/870.16, 340/870.21, 340/870.43, 340/870.37, 340/870.01, 340/870.39, 375/96, 364/724.01, 364/724.05, 341/157, 307/261, 307/262, 307/263, 307/271, 307/519, 328/127
• US Class Current: 340/870.16
• CPC Class Codes: G08C 19/02 in which the signal transmitted is magnitude of current or voltage G08C19/36, G08C19/38 take precedence

Abstract

A digital transmitter with an analog sensor uses an integrating analog-to-digital (A/D) converter to digitize the analog signal from the sensor. The A/D converter produces a digital output which is a continuous, non-rezeroed integrated average of the analog signal, so that the integrated average of the digital output over time does not contain inherent quantization errors. A microcomputer system digitally filters the signal from the A/D converter, and then uses the digitally filtered signal to produce the transmitter output signal. By varying the response time of the digital filter, the response time and resolution of the transmitter can be varied.

Claims

1. A transmitter for providing an output signal as a function of a sensed parameter, the transmitter comprising:

sensing means for providing an analog signal which is a function of the sensed parameter;

integrating analog-to-digital (A/D) converter means for producing a digital signal which is a quasi-continuous, non-rezeroed integrated average of the analog signal;

means for digitally filtering the digital signal to provide a filtered digital signal; and

means for providing the output signal as a function of the filtered digital signal.

2. The transmitter of claim 1 wherein the means for digitally filtering performs one-stage digital filtering of the digital signal.

3. The transmitter of claim 1 wherein the means for digitally filtering performs two-stage digital filtering of the digital signal.

4. The transmitter of claim 3 wherein one stage has a fixed time constant equivalent to an A/D converter update time of the integrating A/D converter means and the second stage has an adjustable time constant.

5. The transmitter of claim 1 wherein the means for digitally filtering performs adaptive filtering of the digital signal.

6. The transmitter of claim 1 wherein the means for digitally filtering comprises a digital computer.

7. The transmitter of claim 1 wherein the integrating A/D converter means comprises a charge balancing voltage-to-frequency converter.

8. The transmitter of claim 1 wherein the sensing means comprises a capacitive sensor and wherein the integrating A/D converter means comprises a charge re-balancing capacitance-to-digital converter.

9. The transmitter of claim 1 wherein the means for digitally filtering the signal is adjustable.