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Calibration: compare a given instrument against a standard instrument to determine its accuracy. Some of the instrument calibration that will be discussed are as follows:
- DC and AC voltmeter
- DC and AC ammeter
- Ohmmeter
The calibration method using potentiometer will also be discussed.
DC Voltmeter Calibration
The test voltmeter reading is compared to the voltage reading obtained using standard instrument.at below,I will teach you about how to calibrate the analog voltmeter.
This is example for voltmeter calibration circuit
Step 1 - Attach the Probe Leads
Attach the red and black leads to the analog voltmeter in the appropriate slots. The slide for the red probe will be marked with an "A" or "V," and the other should be labeled as ground (GRND). The ground slot is for the black probe lead.Step 2 - Turn on the Voltmeter
Switch the power switch for the voltmeter to "On."Step 3 - Switch to the "Ohms" Selection
Turn the dial on the voltmeter to the "Ohms" selection.Step 4 - Check the Voltmeter's Calibration
Next touch the black and red probe leads together. If the analog voltmeter is correctly calibrated, the reading should be "Infinite Ohms" when the probe leads are not touching, and should drop all the way down to "0" when the two probe leads touch together. If the reading is more than 0.05 ohms when the probe leads are touching, the voltmeter is not correctly calibrated.
DC Ammeter Calibration
A DC ammeter can be calibrated using a standard resistor R and a standard voltmeter as shown above.The test ammeter (A) reading is compared to the calculated Ohm’s Law current where the voltage reading obtained across the known standard resistor R, using the standard voltmeter(M).
(1) Ohmmeter Calibration
The Ohmmeter designed around the D’Arsonval meter movement is considered to be an instrument of moderate accuracy.
The accuracy of the instrument can be checked by measuring different values of standard resistance and noting the reading obtained.
A simple 0 Ω calibration is done by connecting its probe together and adjusting the 0 Ω adjustment knob so that its pointer points the 0 Ω mark.
(1) D’Arsonval Meter
A commonly used sensing mechanism used in DC ammeters, voltmeters, and ohm meters is a current-sensing device called a D'Arsonval meter movement. The D'Arsonval movement is a DC moving coil-type movement in which an electromagnetic core is suspended between the poles of a permanent magnet.
Working principle is based on ‘ motor principle ’ where when a current carrying conductor is placed in the magnetic field, it is acted upon by a force which tends to move it to one side and out of the field It is current corresponding device .The deflection of the pointer is directly proportional to the amount of current passing through the coil.
What are the advantages of calibration?
Calibration is proof that the instrument is working properly.
Increases the confidence of instrument user.
Calibration fulfils the requirement of traceability.
Increases power saving and cost saving.
Reduced rejection and failure rate, hence gives higher productivity.
Interchangeability.
The improved product quality and service quality leading to satisfied customers.
Increases safety
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