Appendix 8 Concerning Noise Countermeasures
A17
Appendix
Blocking Noise from External Sources
Keep signal lines away from noise sources
Keep input signal lines (of the thermocouple) away from wiring that is a noise source
(such as power lines, etc.), and make any permanent installation with as much sep-
aration as possible; for example, by runn
ing wires through a separate duct.
Use shielded twisted pair wiring
It is effective to use shielded twisted pairs for the input signal lines (of the thermo-
couple). Twisted pairs are effective for prev
enting electromagnetic induction, and
shielded wires are effective for preventing electrostatic induction.
The shielded wires should basically be grounded on the
signal source side. If it is not
possible to connect the signal source to ground, connect it to the chassis GND on
the LR8431-20. Note that doing so has no effect if the LR8431-20 is not itself con-
nected to ground through the three-prong power cord, etc.
Shielded twisted pair wires for the thermocouple can be obtai
ned from thermocouple
manufacturers.
Normal Mode Noise Countermeasures
Power Supply Line
Electromagnetic
Coupling
Electrostatic
Coupling
Inverter or Commercial
Power Supply
Shielded
Twisted Pair
Wires
The shielding for the signal lines
is grounded on the signal side
Keep the signal lines (of the thermocouple) away from wiring that is a noise source
(such as power lines, etc.). It is also possible to shield the signal lines from elec-
trostatic coupling and to block noise by grounding the shield.
Device being
Tested
Instrument
Thermocouple
If the signal side is not grounded or if it is grounded inadequately, connect the instru-
ment to ground. Also ground the shielding for the signal wires on the instrument side
securely.
Ground Wire
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