AN795

© 2002 Microchip Technology, Inc.

DS00795A-page 2

MOTOR SPEED CONTROL

The motor's speed is measured with the F/V converter, which converts RPM into a proportional voltage. This voltage is used in a

negative feedback system to maintain the motor at the controlled setting.

Motor

Speed

Set

TC9400

F/V

Op

Amp

Pulse Type

Tachometer

(Optical or

Magnetic)

V+

FIGURE 3: Motor speed control.

PROPORTIONAL FLOW-RATE CONTROLLER

A TC9400 F/V converter can be used to regulate the amount of liquid or gas flowing through a pipeline. The flow-rate detector generates

a pulse train whose frequency is proportional to the rate of flow through it. The F/V converts this frequency to a proportional analog

voltage which is used to drive the valve controller. The valve controller regulates the valve so that the flow is steady, even though

pipeline pressure goes up and down. A voltmeter connected to the F/V converter output will indicate the actual instantaneous flow rate.

Flow Rate

Meter

Pulse Output

Flow

Set

Valve

Flow Rate

Detector

TC9400

F/V

Valve

Controller

FIGURE 4: Proportional flow-rate controller.