Azbil Corporation

Kouichirou Murata

Hiroaki Nagoya

Kouji Okuda

Yousuke Inagaki

A positioner is provided with a control calculating portionincluding first and second calculating portions. The first calculating portion, a valve opening detecting portion, and a first pressure sensor are contained in a first case. The second calculating portion, an electropneumatic converting portion, a pneumatic circuit portion, and a second pressure sensor are contained in a second case. The first case is assembled together with the valve, and the second case is located in a position away from the valve. Output signals from the first calculating portion, which are a control signal MV (a PWM signal) and a detected pressure signal S(wherein a detected pressure signal Shas been converted into a digital signal, are sent to the second calculating portion through cables

Positioner

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.

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.

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Tokyo, Japan

Kouichirou Murata