Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut für Berufliche Entwicklung, 201 p.)
 7. Measurement Circuits
 7.1. Measurement Circuits in Direct-current Installations 7.2. Measurement Circuits in Alternating-current Installations 7.3. Measurement Circuits in Three-phase Installations

### 7.1. Measurement Circuits in Direct-current Installations

Voltage measurement (A)

Voltage measurement (B)

By connecting in series of a resistor (Rv), an extension of the measuring range of the voltmeter is obtained

Current measurement (A)

Current measurement (B)

By connecting in parallel a shunt resistor (Rp), an extension of the measuring range of the ammeter is obtained.

Voltage and current measurement for the determination of the resistance

The current-exact connection is used when the resistance (Rx) to be determined, is very high.

Current and voltage measurement for the determination of the resistance

The voltage-exact connection is used when the resistance (Rx) to be determined is very small if the resistance Rx is calculated according to the following equation:

### 7.2. Measurement Circuits in Alternating-current Installations

Voltage measurement (low voltage)

Voltage measurement (high-voltage - voltmeter with voltage transformer)

Current measurement

Current measurement (amperemeter with current transformer)

Power measurement (low voltage)

Power measurement (high voltage)

electric meter connections

electric meter connections

### 7.3. Measurement Circuits in Three-phase Installations

Voltage measurement

2 voltage transformers in V-connection

Current measurement

Current measurement

Power measurement

Single wattmeter method

use:

result:

total power = 3 × measuring result

Power measurement

Two-wattmeter method

use:

measuring instruments of the same type have to be used

result:

total power = P1 + P2,
when P1 > P2, the total power = P1 - P2

Power measurement

Two-wattmeter method
2 movements combined into one instrument

Power measurement

Three-wattmeter method

result: total power = P1 + P2 + P3

Power measurement

Three - wattmeter method
3 movements combined into one instrument

Meter circuit (three-wire meter)

Meter circuit (four-wire meter)

Measurement of the power factor (cos j)

Measurement of the frequency (single frequency meter)

Measurement of the frequency (double frequency meter)

Measurements in a High-voltage Power Plant