JPS57136220A - Control circuit for flow rate controlling valve - Google Patents

Abstract

PURPOSE:To previously prevent a hunting, etc. and to realize the stable control of the water temp., by securing a correspondence between the flow rate of a fluid and the output of a detector and realizing the linear control for them. CONSTITUTION:The output of a temp. deviation arithmetic circuit 13 becomes maximum when the temp. of a load 1 is low and at a temp. T2 at which the deviation to a set temp. TS becomes maximum. Under such conditions, the output current of a variable gain amplifying circuit 14 is set at I2. The amount of gas also becomes maximum Q2 by the current I2. The coil currents I0 and I1 are flowed in correspondence to the temps. T0 and T1 of the load 1. As a result, a coil current IC drops suddenly from I2 to I0 within a range during which the deviation to the set temp. is large. Thus the changing factor of the gas flow rate Q is increased by a degree equivalent to the drop of the current IC. On the contrary, the current IC drops slowly from I0 to I1 in a range of a small deviation to the set temp. And the changing factor of the flow rate Q is reduced by a degree equivalent to the slow drop of the current IC. Thus a linear relation is obtained between the temp. deviation and the gas flow rate Q centering on the current I0.