AN795 Datasheet | Microchip Technology

.. Voltage-to-Frequency/Frequency-to-Voltage Converter Author: Michael O. Paiva, Microchip Technology, Inc. RATIOMETRIC MEASUREMENT (ANALOG DIVISION) One of the most difficult circuits to build is one which will divide one analog signal by another. Two voltage-to-frequency (V/F) converters can do such division with ease. The numerator is counted directly as a signal, while the denominator forms the time base. Latch V1 V2 TC9400 V/F TC9400 V/F ÷N One Shot Counter One Shot Reset Latch V Output = N 1 V2 FIGURE 1: Ratiometric measurement (analog division). RPM/SPEED INDICATOR Flow rates and revolutions per second are nothing more than frequency signals, since they measure the number of events per time period. Optical and magnetic sensors will convert these flows and revolutions into a digital signal which, in turn, can be converted to a proportional voltage by the use of a frequency-to-voltage (F/V) converter. A simple voltmeter will then give a visual indication of the speed. Analog Display Speed Sensor TC9400 F/V RPM DVM Display (Optical or Magnetic) RPM FIGURE 2: RPM/speed indicator. © 2002 Microchip Technology, Inc. DS00795A-page 1 .. 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. V+ Speed Set Motor - Op Amp + TC9400 F/V FIGURE 3: Motor speed control. Pulse Type Tachometer (Optical or Magnetic) 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...