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AN795 PDF даташит

Спецификация AN795 изготовлена ​​​​«Microchip» и имеет функцию, называемую «Voltage to Frequency / Frequency to Voltage Converter».

Детали детали

Номер произв AN795
Описание Voltage to Frequency / Frequency to Voltage Converter
Производители Microchip
логотип Microchip логотип 

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AN795 Даташит, Описание, Даташиты
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AN795
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.
V1 TC9400
V/F
V2 TC9400
V/F
÷N
One
Shot
Output = N
V1
V2
Latch
Counter
One
Shot
Reset
Latch
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
(Optical or Magnetic)
FIGURE 2: RPM/speed indicator.
RPM
DVM Display
RPM
© 2002 Microchip Technology, Inc.
DS00795A-page 1









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AN795
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
FIGURE 3: Motor speed control.
Op
+Amp
TC9400
F/V
Motor
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
pipeline pressure goes up and down. A voltmeter connected to the F/V converter output will indicate the actual instantaneous flow rate.
Flow
Set
Valve
Valve
Controller
Flow Rate
Flow Rate
Detector
Pulse Output
TC9400
F/V
FIGURE 4: Proportional flow-rate controller.
Meter
DS00795A-page 2
© 2002 Microchip Technology, Inc.









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AN795
TEMPERATURE METER
A temperature meter using the voltage output of a probe, such as one of the three shown, can be economically and straightforwardly
implemented with the TC9400 V/F converter. The V/F output is simply counted to display the temperature. For long-distance data
transmission, the TC9400 can be used to modulate an RF transmitter.
Temp
Probe
Preamp
TC9400
V/F
Temperature Display
50/60Hz
Gate
One
Shot
Latch
One
Shot
Reset
Gate
Latch
Reset
Temperature
Probes
A. Thermocouple
Preamp
B. Thermistor
Preamp
C. Transistor
Junction
Preamp
FIGURE 5: Temperature meter.
A/D CONVERSION WITH A MICROCONTROLLER
There are two schemes that can be utilized to accomplish A/D conversion with a microcontroller:
1. Depending on the number of digits of resolution required, VIN is measured by counting the FOUT frequency for 1ms, 10ms,
100ms, or 1 second. The final count is then directly proportional to VIN. (The microcontroller provides the time base.)
2. VIN is measured by determining the time between two pulses (negative edges). FOUT is used as a gate for counting the
microcontroller's clock. The final count will then be inversely proportional to VIN.
By taking the one's complement (changing 1's to 0's and 0's to 1's) of the final binary count, a value directly proportional to VIN will result.
This technique will give a faster conversion time when resolution is very important, but dynamic range is limited.
VIN
TC9400
V/F FOUT
FIGURE 6: A/D conversion with a microcontroller.
PIC
Microcontroller
Digital
Output
© 2002 Microchip Technology, Inc.
DS00795A-page 3










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