Low power process measurement transmitter

Claim 2

A transmitter for deriving energization from, receiving input data modulated on, and transmitting output data by modulation of, a loop current provided by a external power source over a current loop, the transmitter having instantaneous power demands exceeding minimum instantaneous power available from the loop current, the transmitter comprising: sensor means for generating measured values of a process variable; computing means coupled to the sensor means for receiving the measured values, executing a function using the measured value and modulating an output signal with the loop current as determined by the result of execution of the function; receiver means connected between the current loop and the computing means for coupling data received as modulated input signals on the current loop to the computing means, the data including parameters relating to execution of the function; memory means coupled to the computing means for storing the coupled data when energized at a first energization rate; and energization means coupled between the current loop and the memory means for receiving energization from the current loop at a second energization rate lower than the first energization rate and lower than the minimum instantaneous power available from the loop current and for selectively energizing the memory means at the first energization rate.

Claim 3

A transmitter as recited in claim 1 wherein the energization means energizes the memory means at the first energization rate during a WRITE time interval.

Claim 4

A transmitter as recited in claim 2 and further comprising means for allowing a limited portion of the loop current to be coupled from the loop to the energization means, wherein the energization coupled from the energization means to the memory means comprises a WRITE current having a magnitude during the WRITE time interval larger than the magnitude of the portion of the loop current.

Claim 5

A transmitter as recited in claim 3 wherein the energization means comprises storage means for storing energy.

Claim 6

A transmitter as recited in claim 4 wherein the storage means comprises a first capacitor.

Claim 7

A transmitter as recited in claim 5 wherein the storage means further comprises a second capacitor.

Claim 8

A transmitter as recited in claim 6 wherein the energization means further comprises switching means for selectively coupling the first and second capacitors to an energization input for the memory means.

Claim 9

A transmitter as recited in claim 7 wherein the computing means is coupled to the switching means for controlling the selective energization of the memory means.

Claim 10

A transmitter as recited in claim 8 wherein the switching means couples the first and second capacitors in series with the memory means during the WRITE time interval to provide a desired level of excitation to the memory means.

Claim 11

A transmitter as recited in claim 9 wherein the loop current comprises a 4 to 20 mA current.

Claim 12

A transmitter as recited in claim 10 wherein the memory means comprises a non-volatile memory.

Claim 13

A transmitter as recited in claim 11 wherein the non-volatile memory comprises an electrically eraseable programmable read-only memory.

Claim 14

A transmitter as recited in claim 12 wherein the sensor means comprises a capacitive pressure sensor.

Claim 15

A transmitter as recited in claim 13 wherein the energization means further comprises means for limiting the quantity of energy coupled to the storage means.

Claim 16

A process variable transmitter for deriving energization from, receiving input data modulated on, and transmitting output data by modulation of, a loop current signal provided by a external power source over a current transmission loop, the transmitter having instantaneous power demands exceeding minimum instantaneous power available from the loop current signal, the transmitter comprising: first and second terminals for connection of the transmitter into the current transmission loop; sensor means for generating a sensor data signal related to a process variable; memory for storing data including programs and operating parameters for the programs; a computer connected to the sensor means for receiving the sensor signal, for executing programs from the memory using the sensor signal as a data input signal, for developing a data output signal having a relationship to the process variable for transmission onto the current transmission loop, and for determining when instantaneous power demands of the transmitter exceed a predetermined level; and an amplifier under the control of the computer connected between the first and second terminals for modulating the data output signal with the loop current signal; a demodulator connected to the current transmission loop for demodulating data input signals from the loop current signal and transmitting the data input signals to the computer, where the data input signals can include data for storage in the memory; an energy storage network connected to the memory to provide power at the command of the computer at an instantaneous rate exceeding the minimum instantaneous rate available from the current transmission loop; and a voltage regulator connected between the current transmission loop and the computer and providing current to the computer at a first regulated potential and further connected between the current transmission loop and the energy storage network for providing current at a second regulated potential to the energy storage network, wherein the voltage regulator takes power from the current loop at a rate not exceeding the minimum instantaneous power available from the loop current signal.

Claim 17

A process variable transmitter for deriving energization from, receiving input data modulated on, and transmitting output data by modulation of, a loop current signal provided by a external power source over a current transmission loop, the transmitter having instantaneous power demands exceeding minimum instantaneous power available from the loop current signal, the transmitter comprising: first and second terminals for connection of the transmitter into the current transmission loop; sensor means for generating a sensor data signal related to a process variable; memory for storing data including programs and operating parameters for the programs; a computer connected to the sensor means for receiving the sensor signal, for executing programs from the memory using the sensor signal as a data input signal, for developing a data output signal having a relationship to the process variable for transmission onto the current transmission loop, and for determining when instantaneous power demands of the transmitter exceed a predetermined level; and an amplifier under the control of the computer connected between the first and second terminals for modulating the data output signal with the loop current signal; a demodulator connected to the current transmission loop for demodulating data input signals from the loop current signal and transmitting the data input signals to the computer, where the data input signals can include data for storage in the memory; an energy storage network connected to the memory to provide power at the command of the computer at an instantaneous rate exceeding the minimum instantaneous rate available from the current transmission loop; and a voltage regulator connected between the current transmission loop and the computer and providing current to the computer at a first regulated potential and further connected between the current transmission loop and the energy storage network for providing current at a second regulated potential to the energy storage network, wherein the voltage regulator takes power from the current loop at a rate not exceeding the minimum instantaneous power available from the loop current signal.

Claim 18

A process variable transmitter as recited in claim 15, wherein the memory includes a nonvolatile portion which requires instantaneous power at a level exceeding the predetermined level whenever data is to be stored in the nonvolatile portion and wherein the computer transmits a command to the energy storage network to provide energization to the memory at some time after receipt by the computer of input data for storage to the nonvolatile portion.

Claim 19

A process variable transmitter as recited in claim 16, wherein the energy storage network is connected between a terminal of the voltage regulator at which the second regulated level of potential appears and an energization input to the memory.

Claim 20

A process variable transmitter as recited in claim 15, wherein the sensor means further comprise a sensor and an analog to digital converter.