DickDV
Member
While I am very familiar with relay based ladder logic, I have limited experience with PLC's, having concentrated entirely on variable speed motor/drive applications for 15 years.
I would like to consider using a PLC for personal hobby/home use in order to become more familiar with programming. I am looking at about 100 DC signal level inputs and about 100 dry contact or open collector outputs. Response time can be slow--.5 to one second worst case. There would be no analog I/O and no math functions--only lots of logic and a small amount of timing.
Since cost is a factor, my instincts are to buy a minimal processor and load lots of I/O on it. Something tells me that this might not be smart since, if I understand correctly, minimal processors may not have enough internal relays, timers, etc. to do the job with that much I/O.
Also, I was thinking that the Toyo built PLC (marketed by Automation Direct, formerly TI, GE series 90, and possibly Siemens or others) would be a good choice. (Cost again!)
My questions are: how do I approach sizing a PLC and selecting a suitable unit given the above? What traps should I avoid? What about availability of surplus/used equipment?
If you prefer, a response can be made directly to my email: [email protected].
Thanks for your help. I really appreciate it.
I would like to consider using a PLC for personal hobby/home use in order to become more familiar with programming. I am looking at about 100 DC signal level inputs and about 100 dry contact or open collector outputs. Response time can be slow--.5 to one second worst case. There would be no analog I/O and no math functions--only lots of logic and a small amount of timing.
Since cost is a factor, my instincts are to buy a minimal processor and load lots of I/O on it. Something tells me that this might not be smart since, if I understand correctly, minimal processors may not have enough internal relays, timers, etc. to do the job with that much I/O.
Also, I was thinking that the Toyo built PLC (marketed by Automation Direct, formerly TI, GE series 90, and possibly Siemens or others) would be a good choice. (Cost again!)
My questions are: how do I approach sizing a PLC and selecting a suitable unit given the above? What traps should I avoid? What about availability of surplus/used equipment?
If you prefer, a response can be made directly to my email: [email protected].
Thanks for your help. I really appreciate it.