The presentation describes calibration, comparison method of calibration, DMM as standard for calibration. It covers X-Y recorder and plotters.

1. Unit V Calibration & Recorders
Unit V: Instrument calibration: Comparison method, digital
mult-imeters as standard instrument, calibration, instrument
Recorders: X-Y recorders, plotters
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad

2. Instrument Calibration
• Calibration is a process of comparison between a known
measurement (the standard) and the measurement using
instrument under test.
• Typically, the accuracy ratio of the standard to measuring device
should be 10:1 or more. However, accuracy ratio of 4:1 is
acceptable in most cases.
• Bench type digital meters are sufficiently accurate to calibrate
other digital/ analog meters.
• Potentiometer can be employed as calibrator for low level DC
ammeter and voltmeter calibration.
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad

3. Instrument Calibration
Comparison Method
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• Any instrument can be calibrated by comparing its reading with a
more accurate instrument (“Standard”), reading the same quantity.
• A dc voltmeter can be calibrated with using comparison method by
placing a standard meter in parallel and applying a dc voltage.
• The dc voltage applied is adjusted in steps and reading of two
meters is noted (calibration table), which helps in identifying
whether the instrument confirms to specified accuracy or not)
• Adjustments (zero control, calibration adjustments) should be done
before calibration
Variable
DC supply
Standard DC
Voltmeter
DC Voltmeter to
be calibrated

4. Wattmeter Calibration
Comparison Method
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
Variable
DC supply
Standard DC
Ammeter
Variable
DC supply
Standard DC
Voltmeter
Current Coil
Voltage Coil
R
Current Limiting resistor
Wattmeter to
be calibrated
I
V
Exact power P=V.I

5. digital Multi-meters as Standard
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• Best accuracy of analog instruments are  2% of full scale.
• DMM has high accuracy. Typical DMM accuracy is (0.5% + 1 digit).
Thus for 100.0 V reading by a 3 ½ digit DMM accuracy is 0.6%.
• Typical high performance DMM accuracy is (0.1% + 1 digit) and is
sufficiently high to calibrate DMM’s.
• Typical bench type DMM accuracy is (0.01% + 1 digit) and is
sufficiently high to calibrate high performance DMM’s.

6. digital Multi-meters as Standard
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• Calibration of Dc Voltmeter using DMM or DC calibrator require a precise
DC source.
• Precision variable DC voltage source can be made using constant current
source, zener diode and amplifier as shown in the circuit
+
-
R5
-VEE
VCC
Q1
R1 R3
R2
D1Vz
+
-
Iz
VS
+
-
Constant Current Source
Zener diode
R4 Vo
+
-
Amplifier 






5
4
1
R
R
VV zo

7. X-Y Recorders
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• X-Y recorder gives graphic record of relationship of two
variables.
• Ex. V-I characteristics of a diode, speed torque characteristics
of motor, stress strain characteristics, hysteresis characteristics
• Input impedance of X-Y recorder typically varies between 11
K to 1M depending on the voltage range selected.
• One limitation of X-Y recorder is that they operate for low
frequency

8. X-Y Recorders
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• A X-Y recorder use a stationary sheet of chart paper and records
by moving the pen which can move in X & Y direction
simultaneously.
• Pen holder slides along a movable pen carriage
• Movement of pen carriage is controlled by two servomotors (one
for each dimension) through pulley & pulley card arrangement
• Each servomotor is controlled by two inputs.
• Pen down/ up is controlled using a solenoid arrangement.

9. X-Y Recorders
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
Pen
Movable Pen
Carriage
Idler Pulley
Pulley
Card
AttenuatorY input
Balance
circuit
Reference source
Amplifier To Servo
motor
AttenuatorX input
Balance
circuit
Reference source
Amplifier
To Servo
motor

10. Plotters
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NEC 403 Unit V by Dr Naim R Kidwai,
Professor & Dean, JIT Jahangirabad
• A plotter is used to print vector graphics with high print quality
• Single sheet is roller fed back and forward as required while the
pen is moved horizontally to produce the plot or drawing
• Hence vertical movement of paper and horizontal movement of
pen produce the required drawing
• Plotter is used for same applications as that of X-Y recorder
• Plotters are used to draw technical diagrams
• Plotters may use analog or digital printing
HP 7090A plotter