Hioki LR8410-20, Instruction Manual

Page: 331 / 364

Appendix 8 Concerning Noise Countermeasures
A
15
Appendix
What are the sources of noise?
Within a factory, power is provided by large current flows at 50/60Hz. The main loads are
primarily L loads, such as motors and solenoids; in addition, large current pulses are pro-
duced by capacitor input-type switching power supplies for device such as inverters and
high-frequency induction furnaces. Basic wave component leak current, harmonic wave
current, and other types of noise become mixed into the flow from each ground point to
ground lines.
What are the paths of noise propagation?
• Common mode voltage introduced between the ground points of the device
being tested and the measurement unit leaks to the input signal lines
• AC magnetic fields produced by current in power lines couple into loops in the
input signal lines
• Coupling due to electrostatic capacitance between input signal lines and power
supply lines
What is common mode noise?
Noise that is generated between ground and the "+" and "-" input terminals of the instru-
ment.
What is normal mode noise?
Inter-line noise that is generated between the "+" and "-" input terminals of the instru-
ment.
Example of Connections Where Noise Can Affect Measurements
Appendix 8
Concerning Noise Countermea-
sures
Mechanism of Noise Introduction into Thermocouple Temperature
Measurements
Thermocouple
Device being Tested
measurement unit
When using a thermocouple to measure temperature, noise can affect measurements
unless both the device being tested and the measurement units are grounded.
Although there is no problem if the measurement units is running on battery power,
the instrument must be connected to ground if an AC adapter is being used.