Valve positioner with current allocating device
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.
1. A positioner for receiving the supply of an electric current through a pair of electric wires from a higher-level system, and for controlling the degree of opening of a regulator valve in accordance with the value of the supply electric current, comprising:
a constant voltage circuit producing a constant voltage as a local operating power supply from the supply electric current;
a plurality of function circuit portions connected in parallel with the constant voltage circuit;
a supply electric current detector detecting, as the present supply electric current, an actual value for the supply electric current;
a surplus electric current allocating device evaluating whether or not there is, in the detected present supply electric current, surplus electric current that can be directed to the function circuit portion, and, if there is surplus electric current, allocating the surplus electric current to the function circuit portion; and
a storage device categorizing, into a plurality of electric current ranges, the range of electric currents that can be assumed by the supply electric current, and storing a table wherein a combination of the function circuit portions to which the surplus electric current is allocated is established for each category of electric current range,
wherein the surplus electric current allocating device ascertains the category of electric current range to which the detected present supply electric current applies, reads out, from the table, the combination of function circuit portions established for the applicable electric current range category, and allocates the surplus electric current to the function circuit portions of the combination that has been read out.
2. The positioner as set forth in claim 1 , wherein:
in the table, an operating mode of a function circuit portion is specified in the combination of function circuit portions to which the surplus electric power is allocated.
3. The positioner as set forth in claim 1 , wherein:
the combination of function circuit portions to which the surplus electric current is allocated in the table is determined through an instruction from the higher-level system.
4. The positioner as set forth in claim 1 , wherein:
the function circuit portion includes a central calculation processing device; and
the surplus electric current allocating device increases the speed of operation of the central calculation processing device of the function circuit portion by allocating the surplus electric current to the function circuit portion when there is a surplus electric current.