Four high-speed counting channels at 65 kHz sit inside a DIN-rail module smaller than your hand. No counter card, no expansion module, no extra cost — the fast inputs are on the CPU itself, waiting for an encoder, a flow meter, or a production line that moves faster than a relay-logic scan.
Here is the honest part first, because it matters more than the marketing: the SR DC models count fast, but they do not generate high-speed PWM. If your job needs a high-frequency PWM output, this is not the model for it — and no amount of function-block programming changes the hardware.
Which Models, Which Inputs
The 4-channel high-speed counter lives on the four DC models: SR-12DC-DA-R, SR-12DC-DA-R-B, SR-22DC-DA-R and SR-22DC-DA-R-B. Each gives you four counting channels at 65 kHz:
- SR-12DC-DA-R / SR-12DC-DA-R-B — inputs I5, I6, I7, I8
- SR-22DC-DA-R / SR-22DC-DA-R-B — inputs I9, IA, IB, IC
SR-12DC-DA-R also carries the AB encoder function block, which uses inputs I5 and I6 exclusively. If quadrature counting is the job, that is the model to reach for.
The SR-E expansion modules widen your I/O count, but the high-speed inputs belong to the CPU. Plan the fast signals before you choose the expansion, not after.
What 65 kHz Actually Buys You
Sixty-five kilohertz is roughly 3900 RPM from a 1000-pulse encoder, or a bottle line counting well past 30 units a second with room to spare. The point of the hardware counter is that it does not wait for the scan: pulses are totalized continuously by the CPU's counting hardware, and the program reads a stable value on each scan.
Flow-meter totalizing, shaft speed from an encoder, length from a measuring wheel, production counts from a photocell — these are the jobs ordinary inputs miss when the pulses come faster than the scan, and exactly what the 65 kHz counter handles without stretching your cycle time.
Programming Side
The counter is a standard FBD block in free xLogicSoft, wired the same way as any other function block. After the latest SR firmware, the series runs up to 512 function blocks in 32K of program memory, so a counting routine plus the logic around it fits without juggling blocks. On SR-22DC-DA-R and SR-22DC-DA-R-B you get 512 function blocks and 512 application blocks; the AB encoder block on SR-12DC-DA-R covers quadrature input directly.
Memory words are handled with the VB, VW and VD data blocks, so count values, presets and totals live where you can read them on the LCD or over Modbus.
A Bottle-Counting Example
Take a filling line doing 30 bottles a second, with a reject gate after the labeler. The photocell pulse train goes to a high-speed input; the counter total feeds the comparison logic; the gate fires when the count crosses the reject threshold. The counting happens in hardware, so the logic keeps scanning without missing a pulse.
Ten years ago this meant a separate counter module plus a PLC plus a wiring tangle. Today it is one compact CPU, one sensor, one solenoid, and a function block. The special hardware you used to buy is now part of the base spec.
The Scan-Cycle Boundary
Here is the honest boundary: the hardware counts continuously, but the program only sees the count when the scan reads it. For counting, totalizing and events at the millisecond scale, that is exactly right. For a response measured in microseconds — a safety interlock, a crash stop — it is the wrong tool. Keep safety functions on dedicated hardware or interlocked wiring.
A Micro PLC with a 65 kHz counter is not a motion controller, and it does not pretend to be one. Knowing which one your project needs is the first engineering decision.
Wiring That Makes or Breaks Fast Signals
A high-speed input with a noisy signal is a counter that lies. Photocell bounce, an unshielded encoder cable, a VFD switching nearby — all of it arrives as phantom pulses if the wiring is lazy.
Three rules cover ninety percent of the failures: shielded cable grounded at one end; solid-state sensor outputs instead of mechanical contacts; short runs away from power ducts. The CPU offers input filtering for slow signals, but filtering a high-speed count defeats the purpose. Keep the fast inputs unfiltered and clean, and keep the slow inputs filtered against contact bounce.
Test the counting at commissioning with a known pulse source. Ten pulses in, ten pulses counted — the chain is alive. A mismatch is cheaper to find at commissioning than at the first production batch.
The Selection Question
If the requirement is counting — flow, length, speed, production — the SR DC models deliver four channels at 65 kHz with zero extra hardware. If the requirement is high-frequency PWM output, these models are not the answer; the wider xLogic family or a transistor-output controller may fit better. Quote the datasheet of the exact model, and let the datasheet, not my enthusiasm, be the contract.
