Faster PLC
Faster PLC
(OP)
Hello,
I am looking for a faster PLC. I have mainly used PLC's from Automation Direct and have had a couple applications where they did not have the speed required to react quick enough. On a recent application, I wrote a fairly simple program, looked at the scan time while it was running, and it was about 7 - 9 ms. I needed it to be 1 or less. Also I need one with a faster timer. The fastest timer the plc I was using had was .01s. It would be really nice to have a .001s timer. I will appreciate any help that could be given.
Thanks,
Jeremy Estes
I am looking for a faster PLC. I have mainly used PLC's from Automation Direct and have had a couple applications where they did not have the speed required to react quick enough. On a recent application, I wrote a fairly simple program, looked at the scan time while it was running, and it was about 7 - 9 ms. I needed it to be 1 or less. Also I need one with a faster timer. The fastest timer the plc I was using had was .01s. It would be really nice to have a .001s timer. I will appreciate any help that could be given.
Thanks,
Jeremy Estes
RE: Faster PLC
RE: Faster PLC
Many PLC's (don't know about Automation Direct) support interrupts that may be able to respond much quicker than the main program.
Francis
RE: Faster PLC
If you need response times in the order of a few milliseconds, most commercial PLC hardware will not work. If for no other reason the I/O cards can not respond that fast. For this type of application you will need semi-custom microprocessor based solution.
RE: Faster PLC
RE: Faster PLC
RE: Faster PLC
Any microcomputer/controller can outperform most PLC if you
program it in e.g. "C" or assembly.
<nbucska@pcperipherals.com>
RE: Faster PLC
Jeremy - what process do you want to control?
RE: Faster PLC
RE: Faster PLC
latest project I had to solve trigonometric and cubic
equations, perform real time control with 2 uS increments
-- try to do this with PLC !
<nbucska@pcperipherals.com>
RE: Faster PLC
Jeremy
RE: Faster PLC
I would think that the limitation is in the solenoid valves, not the control system. I would think that what you need is two motorized flow modulating valves. Expensive beasties but if the application demands, then you must pay the price.
Using these types of valves then the control logic can use a PID controller (either in the PLC or hardware). The polority of the output of the PID then determines which valve is to be controlled. For example if the output goes positive, control the vent valve, when the output goes negative control the pressure valve.
Sizing of these valve is very important. Too large and you can not get the control you need, too small and the system will not respond fast enough. The valve manufacturers can help you select the size of the valves, it is an arcane disipline.
RE: Faster PLC
Can you make the accumulator tank bigger?
Or have fast and slow solenoids?
And on the control side can you use the run / stop state of the pump to provide some feedforward?
Francis
RE: Faster PLC
RE: Faster PLC