This article is part of a guided learning series on building and analyzing User-Defined Function Blocks (UDFBs).
Canonical Article: Building a User-Defined Function Block (UDFB) Using Siemens TIA Portal
Learning Companion (Q&A): Explore All Questions
You are reading: Question 10
What are appropriate values for timGlitch and timMove?
Answer
Ref: Interposing Relay for Increased Contactor Speed
The reference article contains a strong warning for system level design. Specifically, it demonstrates that an interposing relay is essential for fast turn-off times. There are also other time dependent problems including:
- Speed of the interposing relay and contact bounce
- Speed of the large motor starter contactor plus contact bounce of auxiliary contact
- Flyback suppression
- While not addressed, there is also a time delay associated with a PLC featuring relay outputs
As a first approximation, let’s assume 10 ms for the PLC’s relay, 10 ms for the interposing relay, and 70 ms for the motor starter. We will then multiple this by a factor of 2 to prevent nuisance faults yielding a time timClose in the 200 ms range.
The timGlitch could be shorter as we are primarily concerned with contact bounce. A value of 100 ms should be acceptable.
These number could change considerably if we monitor the output of the motor such as pressure sensor of sail switch. Adjust as necessary.
Tech Tip: It’s been my experience that false alarms are very bad when it comes to human factors. People will learn to ignore that alarms or bypass the system. Given a choice, I recommend erroring on the side reduced nuisance alarms. You will need to balance this with the potential for equipment damage or missed faults.
Article by Aaron Dahlen, LCDR USCG (Ret.), Application Engineer at DigiKey