Metex 3200U Ultrasonic Flow & Level Monitor - Manual (Page 28)

Avoiding noise problems
1. It is recommended that electronic instruments be connected to a relatively clean AC power source.
Use an AC power filter or isolation transformer if necessary.
2. The sensor input line and the control lines (AC or DC) should not be run in the same conduit . The
sensor input should be separated from wires going to inductive loads such as motors, solenoids, relays
and contactors. For best results run the sensor wire in a separate metal conduit. A two-conductor
shielded cable is recommended for the 4-20mA output, the shield should be connected to chassis ground
at the instrument only.
3. For the relay connections, one of most overlooked sources of trouble, noise suppressors are
recommended. Also known as “snubbers” these devices will limit the large spikes produced when the
relay opens, stopping the RFI and also protecting the relay contacts from degrading.
AquaMetrix
Ultrason
Page 28
C
NO
NOISE
SUPPRESSED
AT INSTRUMENT
POWER
240VAC (MAX)
28VDC
NOISE
AT LOAD
(BEST)
SNUBBER LOAD
ULTRASON
NOISE SUPPRESSION ON RELAY OUTPUT
SUPPRESSED
SNUBBER
AQUAMETRIX PART # SNUB