fast PLC need


Thread Starter

hakan kocak

Can anyone tell me the fastest PLC in the market?
In Omron web site their new CJ1 series PLC are considered as the fastest one.

CJ1 needs 0,01 micro second for basic instructions. Output refreshing speed is also important for my application.

Can anyone give me some information?
Yes as of now CS1 and CJ1 from omron happen to be the fastest PLCs in the market. But in my experience some input modules slow the CPU.

Gavin MacLean

I don't know Omron but...

I just did an evaluation for a client, of three PLC's. They ran the same remote type IO, and executed the same code with few drives, some
comms etc. (same result from code different syntax of course). This was with the highest spec of each brand.
Results of scan times (averaged over 500 scans, trended on SCADA and then averaged over an hour):
Allen Bradley ControlLogix5555 - 1.4ms
Modicon Quantum 534 14 - 7ms
GE 90-70 - 28ms
The ControlLogix also has IO module updates down to 2ms, configurable per module or rack and is done asynchronously.
I don't think the lowest boolean execution time means it is the fastest. You have to consider overheads, floating point maths if you have
any, synchronous IO effect on scan etc.

Gavin MacLean
Applicon Australia
[email protected]
From all PLC's I know the SoftPLC from Beckhoff (TwinCAT) outperforms the rest by far.
E.g. TwinCAT is about 25 times faster than the fastest PLC (S7-417) from Siemens (related to Bit-instructions) and about 100 times faster if
a good share of floating point instructions is used.
This comparison was done on a 800 MHz PC. If a state-of-the-art PC is used the numbers above (25, 100) will be significantly higher.
As far as I/O a Profibus DP section running at 12 MBaud should bring you well below 1 msec update rate. If you have an excessive number of
I/O the update time will go a little bit higher. If the update time is too high you can use different proprietary I/0 bus protocols being 3
to 5 times faster than the Profibus.
Fast "basic instruction speed" doesn't mean it is really fast, this is only comparable within their own series. If you are running a huge program with a lots of calculation, the overall scan time of the entire program may still be slow or variable at run time, this is the shortcome of conventional "scan" type PLC. For fast applications and those with control algorythm, a consistant scan time is more important.

For such applications, you need a PLC with time-deterministic prioritized multi-tasking operating system. With this, you can define the fast task with FIXED scan time and highest priority, while leave other less important ones in slower scan time and lower priority tasks. Sometimes you may not even need a fast PLC to do a fast job.

You can find such PLCs in Check your nearest B&R agent, they have new PLC with Pentium 233 CPU for extremely fast

Donald Pittendrigh

Hi All

For lower end PLC take a look at the S7200 range, I have tested this PLC and measured an output switching into a 24VDC relay at speeds in excess of 200hz. Although this is of little practical value it is rather an impressive speed.

Donald Pittendrigh
Keyence has a low cost Visual range of PLC that run over 400 elements in my program @ 1.7ms /scan I also use interrupts to stop a motor
shaft running at 1800 rpm I have a 1024 line encoder hooked to HS input and this stops the motor through the VFD in 1.7 revolutions +/-
3degrees reliably.

Steve Myres, PE

This is not by any means a scientific measurement, but subjectively, the AB Control Logix seems extremely fast for a given code bulk, and tasks are very easy to prioritize and to catagorize between high scheduled and top priority.

Vladimir E. Zyubin

Just a remark:

You speak about special case of geterogeneous systems functioning in case of inadequate calculating power.

For the homogeneous systems the scan type PLC provide the best solution because of minimization of the OSes' overheads (context switching,
priority system, etc.).

Regards. Vladimir.

Thos. D. Moore

Depending upon I/O requirements, I would look at the AB Micrologix. It is used in certain highspeed applications where scan time is absolutely critical. One application that comes to mind is a Lug Loader in a lumber handling system.
I will recomment two solutions:

1) An "Eberle" PLC
2) Siemens S7-300 with an FM352 IO-card, a cam card controller, I have used it an application in Sweden

t stockburger

The Allen-Bradley ControlLogix 5555 processor is the fastest PLC made. It's also easily configured for whatever speed updates you need for I/O
or communications. As for PC based PLC's, they are fast but Bill Gates will have his hand around your throat with these. Stick with the hardware based PLC.
I would agree that the Omron CS1 and soon to be released CJ1 are about the fastest things around at the moment. Have tried many others but nothing beats these.

Depends on the processor and card used. The high end CS1 processor is faster than the low end. Talk to Omron about the fastest input card but I would think the new 96 bit inputs cards for the CS1 would probably be best. You can also, with CX-Programmer, set up the filter time on the input card and also set interrupts when on line and in the IO table area. I have used several CS1s of late and they are very good. Will be better when V2.1 CX-Programmer comes out. You also only have to buy one set of software to cover all Omron PLCs. Price is reasonable too.

Good luck with your project.
Take a look at the SoftPLC brand of PC based PLC's
they don't use any Microsoft and they look almost identical to the AB PLC5, much much faster and about 1/4 of the price.