TOHO ELECTRONICS TTM200 - Manual (Page 115)

48-7009-E 5-45
5.4.8 Position proportional control
■ What the position proportional control is
• In the position proportional control, the temperature of the subject is controlled through adjusting the
flow rate, which depends on the valve opening ratio. The valve opening ratio is controlled by open
or close signal that is output for the valve, where an operating amount is calculated by the PID
control, taking into account the valve motor stroke time. The position proportional control can
control a subject without feedback resistance.
• The valve motor stroke time is defined as time required for a valve from full close to full open.
Sensor
Open signal
Close signal
Controller
Subject of control
Warm water
Discharge of warm water
Valve
Warm
water
• Valve motor drive dead band
The controller for the position proportional control operates output of open or close signal such that
the operating amount of the controller is coincident with the valve opening ratio. To save service
life of the valve, frequent switchover operation for opening and closing the valve must be avoided as
much as possible.
Hence, a dead band is provided on the output switchover points for open and close signals, so that
outputs of both the open and close signals are halted in this band range in order to reduce the
frequency of open and close switchover operations.
Dead band
Opening ratio
MV
Open signal Close signal
• Post-AT initial opening ratio
The operating amount can be set for suppressing undershoot that is possibly generated right after the
termination of AT.
Example: Response in post-AT
ｔ
温度
初期開度＝１００％
初期開度＝０％
AT中 通常制御
Temperature