Mitsubishi Electric FR-D720-0.2K-G Instruction Manual page 190

(2) Signal loss detection (Pr. 122)
If a signal loss (communication stop) is detected between the drive unit and computer as a result of a signal loss detection,
a communication fault (E.PUE) occurs and the drive unit trips. (as set in Pr. 502).
When the setting is "9999", communication check (signal loss detection) is not made.
When the setting value is "0" (initial value), RS-485 communication can be made. However, a communication fault
(E.PUE) occurs as soon as the drive unit is switched to the operation mode (Network operation mode in the initial setting)
with the control.
A signal loss detection is made when the setting is any of "0.1s to 999.8s". To make a signal loss detection, it is necessary
to send data (refer to Mitsubishi inverter protocol control code (page 194), MODBUS RTU communication protocol (page
204)) from the computer within the communication check time interval. (The drive unit makes communication check
(clearing of communication check counter) regardless of the station number setting of the data sent from the master).
Communication check is made from the first communication in the operation mode with control source valid (Network
operation mode in the initial setting).
Example: PU connector communication, Pr. 122 = "0.1 to 999.8s"
Operation mode
Computer
Drive unit
Drive unit
Computer
Pr. 122
Communication
check counter
Always set the communication check time interval before starting operation to prevent hazardous conditions.
Data communication is not started automatically but is made only once when the computer provides a
communication request. If communication is disabled during operation due to signal cable breakage etc., the
drive unit cannot be stopped. When the communication check time interval has elapsed, the drive unit trips
(E.PUE).
The motor can be coasted to a stop by turning ON its RES signal or by switching power OFF.
If communication is broken due to signal cable breakage, computer fault, etc, the drive unit does not detect
such a fault. This should be fully noted.
External NET
ALM OFF
CAUTION
Communication operation and setting
Check start
Fault (E.PUE)
Time
ON
4
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