Before Switching On; Basics; Rms Value; Crest Factor - Hameg HM8115 Manual

"INTERNAL INSTRUMENT SUPPLY" prior to making any
changes to the voltage setting. The fuses must also be
replaced with the appropriate value (see table below) prior
to connecting the power cable. Both fuses are externally
accessible by removing the fuse cover located above the 3
pole power connector.
The fuse holder can be released by pressing its plastic
retainers with the aid of a small screwdriver. The retainers
are located on the right and left side of the holder and must
be pressed towards the centre. The fuses can then be
replaced and pressed in until locked on both sides.
Use of patched fuses or short-circuiting of the fuse holder
is not permissible; HAMEG assumes no liability whatsoever
for any damage caused as a result, and all warranty claims
become null and void.
Fuse type:
Size 5x20mm; 250V AC fuse;
must meet IEC specification 127,
Sheet III (or DIN 41 662
or DIN 41 571, sheet 3).
Time characteristic: time-lag (T).
Line voltage 115V~ ± ± ± ± ± 10%: T 200 mA
Fuse rating for
Line voltage 230V~ ± ± ± ± ± 10%: T 100 mA

Before switching on.

Attention!
Before connecting the power cable to the power socket
(19) marked "INTERNAL INSTRUMENT SUPPLY", the
correct setting of the mains/line switch (20) must be
checked. If a different setting is required, the fuses must
be changed (note "Switching over the mains/line
voltage"). All instruments shipped to European countries
are preset to 230 Vac.

Basics

RMS VALUE

The RMS (Root Mean Square) value describes the quadratic
mean value of an AC parameter (i.e. AC voltage). In case of
sinusoidal AC voltages the RMS value is 1/√2 (0.707) of the
peak value.

CREST FACTOR

The crest factor characterises the shape of an AC parameter
signal. It is the ratio of the peak value to the RMS value
(1.414 for a sine wave).
The accuracy of the calculated RMS value depends on the
crest factor and decreases with higher crest factors. The
maximum permissible crest factor in the specification refers
to full scale of the measurement range. If only a part of the
measurement range is used (i.e. 230 V in 500 V range) the
crest factor may be significantly higher.

POWER

In case of DC parameters (DC voltage, DC current) the power
is the product of current and voltage.
Änderungen vorbehalten / Subject to change without notice
For AC power measurement as well as current and voltage,
the signal shape and the phase relationship must be
considered. If voltage and current are sinusoidal, the power
can be easily calculated when the phase shift between them
is known. Calculation of power parameters becomes
complex with non-sinusoidal wave shapes.
The POWER METER measures the average value of the
instantaneous power and remains accurate whatever the
shape of the signal, provided it is operated within the
specification limits (frequency and crest factor).
When reactive elements are inserted in the generator/load
circuit, the current and voltage are phase shifted with respect
to each other.
With the designations
V = RMS value of a sine wave voltage
I = RMS value of a sine wave current
j = phase shift between voltage and current
the required value can be calculated from the two given
quantities
Apparent Power (Unit Volt Ampere, short sign VA)
VA = V x I
True Power (Unit Watt, short sign P)
P = V x I cos ϕ ϕ ϕ ϕ ϕ
Reactive Power (Voltampere reactive)
Var = V x I sin ϕ ϕ ϕ ϕ ϕ
In case of DC parameters (DC voltage, DC current) the
momentary values are constant and the power is constant
too.
Unlike DC parameters, the momentary value of AC
parameters (which may also be superimposed on DC)
change in amount (amplitude) and sign (polarity) depends
on time. If the polarity of current and voltage is always equal
(no phase shift), the product (current x voltage) is always
positive and the power is converted completely to energy
by the load. There is no power consumption by the load
(inductive, capacitive) in case of momentary values when
(due to phase shift) the current x voltage product becomes
negative. This is called reactive power.
Basics
17