At the running state of PLC, the automatic restoration of HMI default values occurs in the following cases:
1. When the communication cable of the electric control cabinet is interfered by the external interference source;
2. When the purple communication cable connecting HMI to PLC modules performs poorly in communication and contact.
Phenomenon: PLC is in its operating state while the tempering furnace is working. Regarding the HMI parameters such as “preheating furnace low oscillation speed”, “preheating furnace high oscillation speed” and “heating furnace high oscillation speed”, after you change them to 30, 40 and 40 respectively, about 30 seconds later the parameters would be automatically restored to 10, 30 and 30 correspondingly.
Reason: During tempering, disconnection may occur in the electric control system and after several seconds connection will be recovered automatically. When the disconnection occurs, the corresponding LED indicator light will go out but flicker again when the connection is restored.
Solution: Both the automatic restoration of the HMI technological parameters to the defaults and blank screen are caused by the bad contact of the communication cable. Try to plug in the USB interface again. If it works, the communication cable should be blamed. It is suggested to push the shielding layer of the cable aside and ground it nearby or replace the cable.