Abstract: A method of digital temperature compensation uses a digital temperature compensation word to produce a digital word modification of a digital input to a temperature sensitive digital to analog converter hereinafter converter. The method includes the steps of sensing the temperature affecting the converter to produce a digital temperature representation which is used by a digital computer to produce an output in accordance with a characterization equation in the form of Output=f(D, M) where D=digital data and M=f(temperature). The temperature stability of the converter is affected by the temperature stability of a reference voltage circuit used in the converter and having a voltage reference diode. A compensation circuit uses a temperature sensor in the form of a second diode, which is thermally coupled to the reference diode, and a tracking type analog-to-digital converter for converting an analog signal.

Abstract: A communication system for communicating analog and digital data with a process variable, e.g., pressure, transmitter over the two wires which supply power to the transmitter apparatus. The digital communication operation is half-duplex, bit serial transmission and is represented by the currents and voltages in the transmitter communication loop which are selectively introduced between process variable analog data transmissions of 4-20 ma. A plurality of bit cells are provided for each data word or byte between a start bit and a parity bit cell. Following the completion of transmission of the digital data, a predetermined time period is introduced to enable the resumption of transmission of process variable data. Multiple byte digital data transmission can also be effected between process variable analog transmissions by having a byte spacing less than the predetermined time period preceeding the 4-20 ma process variable transmissions.