  Circuits, Formulas and Tables Electrical Engineering - Basic vocational knowledge (Institut f�r 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