Yokogawa DR240 - Manual (Page 75)

3-34 IM DR231-01E
• Insertion of noise filter and noise killer
If the influence from noise cannot be eliminated by the methods described before, use noise
filter or noise killer.
Power line noise rejection
Step 1 : Insert an isolation transformer into the power line.
Increasing impedance to high frequency
with shield, which is grounded
1:1
The instrument (Most of the noise is
high-frequency noise)
100V AC
Power
supply
Step 2 : Insert a power line noise filter (available on the market)
High frequency noise is divided by decreasing impedance to ground through C and
increasing impedance through L.
The instrument
100V AC
L
C
Power
supply
Note 1: Ground the noise filter and the recorder in common.
Note 2: Since insertion of a noise filter increases the by-pass current (regarded as leakage
current), make sure that the leakage current is within the specified value.
• When the noise contains wide frequency components
While one-point grounding is effective at a low frequency, it sometimes forms a loop and
has an adverse effect on a high frequency.
Ex: Connecting a power meter and The instrument grounded at one point to an inverter
AC power meter
The instrument
Noise source
(inverter, etc.)
High-frequency noise
(reverse flow)
One-point
grounding
AC power meter
The instrument
Noise
blocking of reverse flow X
Ferrite beads
(high impedance at high frequency)
Reverse flow of high-frequency to the The instrument is thus suppressed.
The power meter leaks the high-frequency noise component to the
ground and that noise flows back to the The instrument side.
Noise source
(inverter, etc.)
• Input noise rejection
If input noise cannot be rejected by means of one-point grounding or 100-ms integration,
insert capacitor or ferrite beads as they are effective in rejecting pulse noise.
Step 1 : Connect a capacitor between the L input and ground.
C
H
L
The instrument Use a capacitor from a hundred
to thousands of pF which can
withstand high voltages and
must be grounded.
Step 2 : Rejection of pulse noise when grounding is impossible.
C
H
L
The instrument Use a capacitor from a hundred
to thousands of pF.
Ferrite beads
Insert the ferrite beads as necessary.
3.8 Countering Noise