1-6
IM WT1801-01EN
What Is a Measurement Function?
Measurement Function
The physical values (such as rms voltage, average current, power, and phase difference) that the WT1800
measures and displays are called measurement functions. Each measurement function is displayed using
symbols that correspond to its physical value. For example, “Urms” corresponds to the true rms voltage.
Element
Element refers to a set of input terminals that can receive a single phase of voltage and current to be measured.
The WT1800 can contain up to six elements, numbered from 1 to 6. An element number is appended to the
measurement function symbol for the measured data that the WT1800 displays, so that you can tell which data
belongs to which element. For example, “Urms1” corresponds to the true rms voltage of element 1.
Wiring System
You can specify five wiring systems on the WT1800 to measure the power of various single-phase and three-
phase power transmission systems: single-phase, two-wire; single-phase, three-wire; three-phase, three-wire;
three-phase, four-wire; and three-phase, three-wire with three-voltage, three-current method.
Wiring Unit
The wiring unit is a set of two or three input elements of the same wiring system that are grouped to measure
three-phase power. There can be up to three wiring units: ΣA, ΣB, and ΣC.
Σ Functions
The measurement function of a wiring unit is called a Σ function.
For example, “UrmsΣA” corresponds to the average of the voltages of the input elements that are assigned to
the wiring unit
ΣA. The average value represents the true rms value.
Three-phase,
three-wire
Σ
A
Element
1
Element
2
Element
3
Element
4
Three-phase,
three-wire
Σ
B
Wiring system
Wiring unit
Voltage input
Current input
Element
5
Element
6
Three-phase,
three-wire
Σ
C
Measurement Period
For information about the measurement period for computing measurement functions, see “Measurement Period
(SYNC SOURCE).”
1 Items That This Instrument Can Measure
