Posted on 5th June 2020
This was an interesting job that was a simple fix but was causing our customer a massive headache as it was inhibiting his machine from running.
A chance occurrence caused the PLC in the 1.5 year old Doosan DNM 5700 VMC with Siemens 828D control to lock up and generate a spurious alarm indicating that the side maintenance doors were open, even though they weren’t and no input signals from the door sensors were missing.
The alarm wouldn’t reset, not even with a power cycle, a critical machine dead in the water for no apparent reason. After checking all relevant inputs, sensors and wiring were all correct, we interrogated the PLC with a Simatic Field PG and 828D PLC software. This indicated a bit in a datablock (DB) was latched high, the only way to reset it was within the NC/PLC variables option on the HMI. This cleared the alarm and it didn’t return.
We showed the customer how to overcome this issue if it ever reoccurred. The machine is up and running again and the customer is happy, all due to having the right tools and knowledge for the job.
Siemens hardware and software is what we specialise in, from diagnosis to cure speak to us with any faults on Siemens Controls and Drives.
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