Low power transmitter

• US 4,339,750 A
• Filed: 08/20/1980
• Issued: 07/13/1982
• Est. Priority Date: 08/20/1980
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Delacruz, Moises A.
• Primary Examiner(s): Brigance, Gerald L.
• Application Number:
  US06/179,711
• Time in Patent Office: 692 Days
• Field of Search: 340/870.37, 340/870.3, 340/870.39, 324/60 R, 324/60 C, 324/60 CD
• US Class Current: 340/870.37
• CPC Class Codes: G08C 19/10 using variable capacitance

Abstract

A low power transmitter has a D.C. Power supply for providing the transmitter with power. The supply is coupled to a voltage regulator for regulating the voltage to the transmitter and the regulator is further coupled to an oscillator which provides a time varying voltage signal to a capacitance sensor which varies as a function of the parameter to be sensed. The charging and discharging current pulses from the sensor, as affected by such sensors, are rectified and fed to an oscillator driver amplifier which controls the time varying voltage as a function of such rectified signals. The rectified signals are also fed to a low power consumption output amplifier which provides a zero based D.C. voltage output signal representative of the parameter to be sensed along two wires. The transmitter operates on low voltage and has a low power consumption.

Claims

1. A low power transmitter having power supply means for providing the transmitter with power,

voltage regulator means coupled to the power supply means for regulating the voltage provided for the transmitter,

oscillator means coupled to the regulator means for providing a time varying voltage as a function of the voltage of the regulator means,

sensor means coupled to the oscillator means for receiving the time varying voltage therefrom and for excitation thereof, said sensor means being responsive to changes in a parameter to be sensed and affecting the time varying signal responsive to the change in the parameter, said sensor means further including rectifier means for rectifying the affected time varying signal to provide a D.C. signal as a function of the parameter to be measured,

driver means coupled to the sensor means to drive the oscillator responsive to the D.C. signal,

low power consumption amplifier means coupled to receive the D.C. signal and to provide a zero based D.C. voltage output signal representative of the parameter to be measured along two wires,

said voltage regulator means further comprising voltage reference means for establlishing a stable reference voltage,

error amplifier means coupled to the reference voltage means to provide an error signal as a function of the voltage from the reference voltage means and the voltage from the power supply means, and

pass element means coupled to receive the error signal and coupled to the power supply to regulate transmitter voltage at a level not substantially greater than ten volts,

the voltage regulator means, oscillator means, sensor means, driver means and low power consumption amplifier means providing such D.C. voltage output signal when the power supply means is limited to not substantially greater than ten volts.

2. Apparatus according to claim 1 wherein the voltage reference means is a zener diode.

3. Apparatus according to claim 2 wherein the error amplifier means comprises comparator means having

first input means coupled to the reference voltage means, a voltage divider coupled across the output of the pass element means, second input means coupled to such voltage divider, and output means to provide an error signal as a function of the signals at the first and the second input means.

4. Apparatus according to claim 3 wherein the transmitter further comprises second voltage means coupled from the output of the pass element means to the driver means for providing a desired time varying voltage for the sensor means.

5. Apparatus according to claim 4 wherein the pass element means is a field effect transistor.

6. Apparatus according to claim 5 wherein the sensor means comprises at least a first capacitor plate means, and a diaphragm which forms a second plate, the first plate means and second plate forming at least one capacitor for measuring pressure.

7. Apparatus according to claim 6 wherein the power supply means is a battery and integral to the transmitter.

8. Apparatus according to claim 7 wherein the power supply means further comprises a solar cell.

9. Apparatus according to claim 6 wherein the power supply means is external from the transmitter and a third wire couples the power supply to the transmitter.