Appendix 8 Concerning Noise Countermeasures - Hioki Memory HiLogger LR8401-20 Instruction Manual

Appendix 8
Mechanism of Noise Introduction into Thermocouple Temperature Mea-
surements
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 HiLogger 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 HiLog-
ger.
What is normal mode noise?
Inter-line noise that is generated between the "+" and "-" input terminals of the HiLogger.
Example of Connections Where Noise Can Affect Measurements
Device being
When using a thermocouple to measure temperature, noise can affect measurements
unless both the device being tested and the HiLogger are grounded.
Although there is no problem if the HiLogger is running on battery power, the HiLogger
must be connected to ground if an AC adapter is being used.

Appendix 8 Concerning Noise Countermeasures

Concerning Noise Countermea-
sures
Thermocou-
ple
A
HiLogger
13