Abstract: A field apparatus for controlling a controlled element includes a diagnosis unit for diagnosing abnormality of the field apparatus and/or the controlled element and a bidirectional digital communication device to send a digital signal which shows a diagnosis result to outside and to receive a digital signal from outside in order to execute a control of the controlled element. Other predetermined functions are effected based on a command signal in the form of an analog signal received from outside by a analog communications device of the apparatus. Electric power for operation is supplied through a switching means that can switch either a electric power that is supplied by the analog communications device or a electric power that is supplied by the bidirectional digital communication device.

Abstract: A temperature information detecting device for an angle sensor is provided for detecting only temperature-dependent components based on middle-point potentials when a constant current is supplied to a bridge circuit for an angle sensor, for acquiring a temperature of the angle sensor from the temperature-dependent components, for employing compensating information corresponding to the acquired temperature without separately providing any additional temperature sensor, and for making temperature compensation of the output of the temperature sensor in automatically controlling the valve opening of a flow control valve.

Abstract: A field apparatus (1a) comprises a diagnosis unit (11) diagnosing abnormality of oneself or a controlled element and a bidirectional digital communication means (22) to send a digital signal which shows a diagnosis result to outside and to receive the digital signal from outside in order to execute a control of controlled element and other predetermined functions based on a command signal received by a analog communications means (17) that can receive a analog signal from outside. A electric power for operation is supplied through a switching means (18, 53) that can switch either a electric power that is supplied by the analog communications means (17) or a electric power that is supplied by the bidirectional digital communication mean (22).

Abstract: A temperature information detecting device for an angle sensor is provided for detecting only temperature-dependent components based on middle-point potentials when a constant current is supplied to a bridge circuit for an angle sensor, for acquiring a temperature of the angle sensor from the temperature-dependent components, for employing compensating information corresponding to the acquired temperature without separately providing any additional temperature sensor, and for making temperature compensation of the output of the temperature sensor in automatically controlling the valve opening of a flow control valve.

Abstract: A current holding circuit of a two-wire instrument which includes a transmitter and a receiving resistor, remotely located from the transmitter, for detecting a signal from the transmitter as a change in loop current, and to which a commuication device is connected, includes a current detecting unit, a sample-hold unit, and a current control unit. The current detecting unit includes a reference resistor for converting the loop current into a voltage and a first operational amplifier for receiving the voltage obtained by the reference resistor at the noninverting input terminal. The sample-hold unit holds an output from the current detecting unit. The current control unit supplies an output from the sample-hold unit to the inverting input terminal of the operational amplifier and controls the loop current on the basis of the output from the operational amplifier, thereby holding the loop current at a constant value.

Abstract: A method of communicating data between first and second communication apparatus having the steps of transmitting line current from the first communication apparatus to a transmission line interconnecting the first and second communication apparatus, the line current being controlled at an analog value representing analog data and having superimposed thereon a digital signal representing digital data, receiving at the second communication apparatus the analog and digital data transmitted by the first communication apparatus, controlling the transmission line voltage at an analog value for transmitting analog data from the second communication apparatus to the first communication apparatus and superimposing on the voltage containing the analog data a digital signal representing digital data, and receiving at the first communication apparatus the analog and digital data transmitted by the second communication apparatus.

Abstract: A communication apparatus for receiving both power and a sensor signal over the same transmission line having a first variable impedance element and a receiving impedance element connected in series across the transmission line, a second variable impedance element and a series impedance element connected in series across the transmission line, and a control circuit for controlling the first variable impedance element to maintain the transmission line voltage constant and for controlling the second variable impedance element to maintain the current flowing through the series impedance element constant, the control circuit simultaneously controlling the first and second variable impedance elements to maintain the current flowing through the series impedance element constant while transmitting data over the transmission line.

Abstract: A receiving apparatus for receiving an electrical signal over a 2-wire transmission line, the electrical signal having a signal component and a bias component, the bias component being used by the receiving apparatus for providing power to the receiving apparatus, the receiving apparatus having a first variable impedance element and a receiving impedance element connected in series across the transmission line, a second variable impedance element and a series impedance element connected in series across the transmission line, and a control circuit for controlling the first variable impedance element to stabilize the voltage across the transmission line to a constant value and for controlling the second variable impedance element to stabilize the current flowing through the series impedance element to a constant value, so that a current flowing through the receiving impedance element relates to the signal component and the current flowing through the series impedance element relates to the bias component.

Abstract: An electromagnetic flowmeter for electrically measuring a flow rate of a fluid flowing through a measuring pipe has an insulating lining which lines the measuring pipe. A conductive powder is mixed in parts of the insulating lining. The measuring pipe is short-circuited with the fluid through the conductive powder, thereby providing a reference potential of detected current corresponding to the flow rate of the fluid.