VTI Instruments Metek EX1202 - Page 86

VTI Instruments Corp.
86 Basic EX1200 DMM Operation
Waveform
Example
Crest Factor
Sine
1.414
Full-wave Rectified Sine
1.414
Half-wave Rectified Sine
2
Triangle
1.732
Square Wave (Symmetrical)
1
Repeating Pulse (PWM)
T
t
1
1
t
T
FIGURE 4-10: CREST FACTORS FOR COMMON WAVEFORMS
Crest factor related errors are specified in the DMM specifications on page 20. The specifications
are for non-sine waveforms that are above 100 Hz when the Low filter (3 Hz) is used. The
measurement error can be determined for non-sinusoidal input using the deratings specified in the
datasheet.
Loading Errors
In ACV mode, the input of the EX1200 DMM appears as a 1 MΩ resistance in parallel with
100 pF of capacitance. The cabling used to connect the signals and the switch module used to
route the signals to the multimeter also add additional capacitance and loading. When connected to
high output impedance sources, like high-voltage probes, an error will be present as the result of
loading on the source. This error can be calculated using the following equation:
 





























 1
1
1
1
1
21
1
100%
2
s
s
s
in
RM
M
RM
RM
fC
Error

Where:
R
s
= source resistance
f = input frequency
C
in
= input capacitance (100 pF) plus cable capacitance plus switch capacitance