Metex 3200U Ultrasonic Flow & Level Monitor - Manual (Page 27)

INSTALLATION CONSIDERATIONS IN NOISY ENVIRONMENTS
AquaMetrix’s instruments are designed with a high degree of noise immunity for use in industrial
environments. Noise interference can still occur if certain minimal considerations are not adhered to
when installing the equipment.
Noise
When relay contacts are used to switch inductive loads, such a auxiliary relays or solenoids, extremely
large voltage spikes can be generated when the relay contact opens producing what is known as
Radio-Frequency Interference or “RFI” or just “noise”.
These voltage spikes can also be coupled from power lines that are powering equipment that contains
S.C.R. circuitry such as VSD controllers, or lines that are actuating AC or DC solenoids or actuators.
There are three major ways that noise spikes can enter the instrument.
1. Via the AC power input lines.
2. Via the Sensor input line.
3. Via the output lines (relay connections and 4-20mA output)
Symptoms of RFI produced by relay activation
If the instrument shows the following symptoms suspect RFI.
- The Alphanumeric display (bottom display) blinks continuously as if power was being turn
off and on (i.e instrument resets continuously).
- Keypad does not respond or instrument resets to run mode from inside the menu.
- The instrument calibration is lost.
- The message
"
MEM CORRUPTED
" is shown.
- Relays trip erratically.
- Both digital displays go blank as if power was OFF.
Symptoms of noise on sensor input and/or 4-20mA lines
- Instruments readings are erratic or high when actual value is low
- The Alphanumeric display (bottom display) blinks continuously as if power was being turned
off and on i.e instrument resets continuously.
- Instrument “beebs” intermittently even if the Keypad is not pressed.
AquaMetrix
Ultrason
Page 27