Countermeasures On Common Interference; Interference On Meter Switches And Sensors - Kruger Ecowatt K320 Series Operation Manual

Ecowatt Drive K320 series
®

7.7 Countermeasures on common interference

7.7.1 Interference on meter switches and sensors

Interference phenomenon
Pressure, temperature, displacement, and other signals of a sensor are collected and displayed
by a human-machine interaction device. The values are incorrectly displayed as follows after
the VFD is started:
1. The upper or lower limit is wrongly displayed, for example, 999 or -999.
2. The display of values jumps (usually occurring on pressure transmitters).
3. The display of values is stable, but there is a large deviation, for example, the temperature
is dozens of degrees higher than the common temperature (usually occurring on
thermocouples).
4. A signal collected by a sensor is not displayed but functions as a drive system running
feedback signal. For example, the VFD is expected to decelerate when the upper pressure
limit of the compressor is reached, but in actual running, it starts to decelerate before the
upper pressure limit is reached.
5. After the VFD is started, the display of all kinds of meters (such as frequency meter and
current meter) that are connected to the analog output (AO) terminal of the VFD is severely
affected, displaying the values incorrectly.
6. Proximity switches are used. After the VFD is started, the indicator of a proximity switch
flickers, and the output level flips.
Solution
1. Check and ensure that the feedback cable of the sensor is 20 cm or farther away from the
motor cable.
2. Check and ensure that the ground wire of the motor is connected to the PE terminal of the
VFD (if the ground wire of the motor has been connected to the ground block, you need to
use a multimeter to measure and ensure that the resistance between the ground block and
PE terminal is lower than 1.5 Ω).
3. Try to add a safety capacitor of 0.1 μF to the signal end of the feedback signal terminal of
the sensor.
4. Try to add a safety capacitor of 0.1 μF to the power end of the sensor meter (pay attention
to the voltage of the power supply and the voltage endurance of the capacitor).
5. For interference on meters connected to the AO terminal of a VFD, if AO uses current
signals of 0 to 20 mA, add a capacitor of 0.47 μF between the AO and GND terminals; and if
AO uses voltage signals of 0 to 10 V, add a capacitor of 0.1 μF between the AO and GND
terminals.
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Troubleshooting