Meters and Measurement

It is the use of measuring devices to determine the values of different quantities

Measurement

It is the measure of consistency or repeatability of measurements

Precision

What is the formula for precision?

It is the degree of exactness of a measurement when compared to the expected value

Accuracy

What is the formula for accuracy?

It is the deviation of reading from expected value

Error

What is the formula for absolute error? Is it unitless?

No

What is the formula for relative error? Is it unitless?

Yes

What is the formula for percent error?

D’Arsonval meter is also known as?

Permanent-Magnet Moving-Coil

What are D’Arsonval meter’s “most”?

• most popular

• most widely used

• most sensitive

D’Arsonval meter operates upon the interaction of what?

magnetic fields between permanent magnet and electromagnet

D’Arsonval meter reacts directly to what? propotional to?

current / proportional to current

D’Arsonval meter measure (direct and indirect)

direct

• current

• DC

indirect

• votlage and resistance

• AC (add rectifier)

D’Arsonval meter patented by? when?

Jacques d’Arsonval / 1881

What are the three forces involved in the operation of PMMC?

• Deflecting - “magpapagalaw”

• Controlling - “magbabalik”

• Damping - “magtitigil”

A device that indicates the amount of current flowing

Ammeter

Ammeter is connected in?

Series

It is a precision resistor connected across the meter movement and its effect is to extend the range of the ammeter

Meter shunt

A shunt exceeds the range of a 50 uA meter movement to 1 mA. How much is the current through the shunt at quarter-scale deflection?

237.5 uA

A 50 uA meter movement has a resistance of 1000 ohms. What Rsh is needed to extend the range to 500 uA?

111.1 ohms

An ammeter has a PMMC Instrument with a coil resistance of 99 ohms and FSD current of 0.1 mA. Shunt resistance equals 1 ohm. Determine the total current passing through the ammeter at 0.5 FSD.

5 mA

It is also known as universal shunt and used for multiple range resistor.

Ayrton Shunt

Errors in ammeter reading is due to […] effect

Insertion

What is ammeter ideal value?

0 ohms

It is an instrument used for measuring electrical potential difference between two points.

Voltmeter

Voltmeter is connected in?

Parallel

A high resistance resistor in series with the meter movement that increases the range of the voltmeter

Multiplier resistor

For a 30V range, a 50 uA, 2k ohm meter movement needs a multiplier resistor of

598k ohms

Compute the value of the multiplier resistor for a 10-Vrms ac range on an ac voltmeter which uses half-wave rectification and has a full scale current of 1mA and internal resistance of 300 ohms

4.2k ohms

A PMMC instrument with FSD of 100 uA and a coil resistance of 1k ohm is converted to a 50 V Voltmeter using a multiplier resistor of 499k ohms. Calculate the applied voltage when the instrument indicates 0.2 of FSD.

10 V

Errors in voltmeter is due to […] effect

Loading

What is the ideal value of a voltmeter?

infinite

It indicates the voltmeter’s resistance independently of range

ohm-per-volt rating

Ohms-per-volt rating is also called?

Sensitivity of the voltmeter

What is the formula of sensitivity of voltmeter?

What is the sensitivity of ac voltmeter?

It is an electrical instrument that measures electrical resistance, the opposition to an electric current

Ohmmeter

Erros in ohmmeter is due to?

Battery Voltage Decay

What is the formula for deflection factor?

The ohmmeter has a meter movement of 100 uA and 2k ohms resistance. The open circuit voltage is 10V. The ohmmeter is zeroed and then an unknown resistance is measured, which produces quarter-scale deflection. What is the value of the unknown resistor?

300k ohms

If you insert an ammeter in a circuit, what will happen?

A. the ammeter increases the resistance of the circuit and therefore, increases the current in the circuit
B. the ammeter decreases the resistance of the circuit and therefore, reduces the current in the circuit
C. the ammeter decreases the resistance of the circuit and therefore, increases the current in the circuit
D. the ammeter increases the resistance of the circuit and therefore, reduces the current in the circuit

D

Technician A says voltmeter is connected in series to measure voltage. Technician B says it is connected in parallel. Who is correct?

A. Technician A only
B. Technician B only
C. Both Technicians A and B
D. Neither Technicians A nor B

B