Azbil Corporation

Hiroaki Nagoya

Kouji Okuda

Kouichirou Murata

Kentaro Ohya

Yousuke Inagaki

Yoshio Maehana

In a positioner, a control calculating portion and a valve opening detecting portion are contained within a first case, and an electropneumatic converting portion and a pneumatic circuit portion are contained within a second case. The first case, which contains the control calculating portion and the valve opening detector, is assembled together with the valve, and the second case, which contains the electropneumatic converting portion and the pneumatic circuit portion, is located in a position away from the valve. A control signal MV, which is a PWM signal (a digital signal), is sent through a cable from the control calculating portion to the electropneumatic converting portion.

Positioner

A field device has a primary power supply generating circuit that generates a primary power supply from an electric current that is supplied through a pair of electric wires from a higher-level system, and a calculation processing portion and various functional circuit portions, which operate based on a supply of an operating power supply electric current produced from the primary power supply. The field device also has an operating power supply electric current supplying unit that supplies the operating power supply electric current to a calculation processing portion with maximum priority. The calculation processing portion receives the operating power supply electric current supplied with maximum priority, clears a self-reset operation after starting up itself, and then directs sequentially, following a predetermined sequence, supply of the operating power supply electric current to each of the various functional circuit portions.

Field device

The range of electric currents that can be assumed by a supply electric current is categorized into a plurality of electric current ranges, where, for each electric current range category, there are combinations of functions, wherein the total value for the electric current required is less than the upper limit value, and no less than the lower limit value, for the electric current range established, and a table wherein these combinations are established is stored in memory. An actual value is detected for a supply current I to ascertain the category of electric current to which the supply electric current I applies, the combination of functions established for the applicable category of electric currents is read out from the table, and operation of the function circuit portions for the functions of the combination that has been read out is enabled, and operation of the other function circuit portions is disabled.

A coil of an electro-pneumatic converting portion is connected in parallel with a constant voltage circuit. An electric current regulating portion is provided in a supply line for an electric current to the coil. The regulating value for the electric current in this electric current regulating portion is controlled by an instruction from a CPU. The CPU detects, as a present supply electric current, an actual value for the supply electric current from a higher-level system, and evaluates whether or not there is, in the present supply electric current, a surplus electric current that can be directed to the electro-pneumatic converting portion. The supply electric current can be in excess of 4 mA and is the surplus electric current, and if there is a surplus electric current, then a command is sent to the electric current regulating portion so as to allocate that surplus electric current to the coil.

Valve positioner with current allocating device

To provide reliable notification of a fault state when a power supply to a calculation processing portion is in the OFF state when a power supply to a communication processing portion is in the ON state. An isolating circuit, an inverting circuit inverting a signal branch-outputted through an output line of the isolating circuit, and a selecting circuit that uses the signal outputted from the output line of the isolating circuit as a first input and the inverted signal from the inverting circuit as a second input, to select either the first input or the second input, depending on a selection setting status thereof, to output the selected signal to the communication processing portion are provided. A +5 V voltage is applied through a resistor to the output line of the isolating circuit. This +5 V voltage is produced through the power supply supplied from the second double-wire transmission path.

A variable impedance circuit is provided as an active load between an input line L1 and an output line L2. This circuit has low impedance with respect to a DC electric current signal and has high impedance with respect to an AC electric current signal, structured from a series circuit of resistors R1, R2, and R3 connected between lines L1 and L2; a transistor Q1 having the collector connected to the line L1 and the base connected between the resistors R2 and R3; a resistor R4 connected between the emitter of the transistor Q1 and the line L2; a capacitor C1 with one end connected between the resistors R2 and R3; a resistor R5 connected between the other end of the capacitor C1 and the line L2; a capacitor C2 having one end connected between the resistors R1 and R2; and a resistor R6 connected between the other end of the capacitor C2 and the line L2.

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Tokyo, Japan

Hiroaki Nagoya