Digital Voltmeter, Digital Ammeter and Digital Multimeter...Advantages of Digital meters 3 Very high...
Transcript of Digital Voltmeter, Digital Ammeter and Digital Multimeter...Advantages of Digital meters 3 Very high...
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Digital Measurements
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Submitted By:
Mr. Santosh Kumar Gupta
Assistant Professor
EE Department, SIT Sitamarhi
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Contents
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Advantages of Digital meters Digital Components Digital Voltmeter(DC) Digital Voltmeter(AC) Measurement of Current Measurement of Resistance A complete DMM Measurement of hfe A digital voltmeter and ohmmeter using
Arduino.
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Advantages of Digital meters
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Very high accuracy (5 to 0.05%)
Has very input impedance (2MΩ)
which ensures less loading effect on
the input.
The numeric display of digital meters
provide zero parallax error.
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Digital Components
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Crystal Oscillator
Counter
A/D Converter
Voltage-Frequency Converter
Phase Locked Loop
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Crystal Oscillator
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A piezoelectric crystal is used.
Generally, a1MHz crystal is used
which produce a clock pulse of 1MHz.
Used to provide the clock pulses.
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Counters
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A/D Converters
Converts Analog data to Digital data
using a dual slope converter.
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Voltage-Frequency Converter
Produces a frequency signal which is
proportional to the input voltage.
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Digital Voltmeter(DC)
The voltage is first attenuated and
then converted into a digital word
which is displayed.
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Role of ADC
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The lines supplied by the ADC to the
display consists of
◦ The digital word
◦ A latch
◦ Start bit
◦ Polarity information
◦ Floating point information
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Features
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Polarity detection
Auto ranging
Auto zeroing
Polarity detection:
The information is given by the ADC.
When the voltage is +ve, the characteristic
curve of the converter is in first quadrant.
The characteristic curve will be in the fourth
quadrant, if the voltage is –ve.
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Auto Ranging
Two comparators are used.
The typical ranges are,
◦ 0 to 100 mV
◦ 100 mV to 1 V
◦ 1 V to 100 V
◦ 100 V to 1000V
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Auto Zeroing
Zero is displayed during the start of
conversion.
This is achieved by discharging the
capacitance to the ground properly.
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DVM (AC)
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The AC is processed first i.e., phase
compensated attenuation with
rectification and filtering is done.
The dc voltage obtained is converted
into a digital word, which is displayed.
For high frequencies, a precision
diode with small reverse recovery time
is required.
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DVM(Low voltage AC)
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For measurement of voltages in the
range between 1 nV and 10 nV, the
voltage is converted into a frequency
signal by a voltage-frequency
converter or phase locked loop.
The frequency is measured by proper
networks.
This reduces the effect of noise
through ADC.
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Phase locked loop
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Measurement of current by DMM
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Typical ranges
◦ 0 to 10 mA
◦ 10 mA to 100 mA
◦ 100 mA to 1A
◦ 1 A to 10A
Auto ranging is available.
Auto zeroing is also available.
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Two ways of measurement
◦ Measuring the voltage drop across a
resistance.
◦ Current frequency converter.
In the first method, current is passed
through a constant resistance. The
voltage drop across it is measured
using a DVM.
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In the second method, a current-
frequency converter is used.
The output of comparator is a
frequency which is proportional to the
current.
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Measurement of Resistance using DMM
A constant current is passed through
the unknown resistance and the drop
across it is measured by a DVM.
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Complete circuit of a DMMThe switches are coupled to each other.
The display is generally 3 digits (-1999 to 1999)
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Measuring hfe of a transistor
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Hfe measurement
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A small project: Digital Voltmeter
using ATMEGA328P
ATMEGA328P
A0 GND
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Direct voltage measurement:
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RANGE EXTENDED VOLTMETER
ATMEGA328P
A0 GND
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CODE:
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float voltage, previousvoltage=0;
void setup()
{
serial.begin(9600);
}
void loop()
{
voltage=analogRead(A0)*0.00488758553;
if(voltage!=previousvoltage)
{
Serial.println("the voltage is");
Serial.println(voltage);
previousvoltage=voltage;
}
delay(500);
}
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Ohmmeter using arduino
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Arduino code
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int analogPin= 0;
int a;
int Vin= 5;
float Vout= 0;
float R1= 1200;
float R2= 0;
float buffer= 0;
void setup()
{
Serial.begin(9600);
}
void loop()
{
a= analogRead(analogPin);
if(a)
{
buffer= a * Vin;
Serial.println(a);
delay(1000);
}
}
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Challenges
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If you use a small value of known
resistance to measure a large value of
resistance the value gives up an error,
So use known resistance which is
some what closer to the measuring
resistance to give an output with
greater accuracy.
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References
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Sawhney A K, “A Course in Electrical and
Electronic Measurement and Insrtumentation”,
Dhanapat Rai & Sons, New Delhi, 2011.
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Thank You!!
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