Omron CJ1W-CT021 — 2-Channel Counter Unit, 500 kHz
SKU: CJ1W-CT021USD 160.00
CJ-series 2-channel high-speed counter, 500 kHz line-driver / 50 kHz open-collector, 32-bit range, 2 in / 2 out.
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Product Overview
The Omron CJ1W-CT021 is a Special I/O unit that adds two independent 32-bit counters to any CJ-series PLC. Each channel counts encoder pulses at up to 500 kHz on a line-driver input or up to 50 kHz on an open-collector input, so one unit handles either one high-resolution encoder plus a low-resolution backup or two independent axes. Counter modes include simple up/down, ring (preset wrap), and linear (overflow flag). Two 24 VDC digital inputs and two NPN transistor outputs per channel give discrete I/O, and 30 internal "soft outputs" trigger inside ladder without using an output terminal. The CT021 sits in any CJ-series CPU or expansion rack slot and communicates with the CPU through a fixed CIO/DM area in CX-Programmer; a single CJ system can hold up to 24 CT021 units.
Choosing 2-channel vs 4-channel
The CT021 is the standard 2-channel pick. If your build needs more channels, step up to the CJ1W-CT041 (4 channels at 500 kHz line driver) instead of stacking two CT021 units. The CT021 matches the older C200H-CT021 on connector pinout and software, so it is a like-for-like drop-in across the CJ, CS, and C200H Alpha racks.
Wiring the encoder
A 24 VDC NPN open-collector encoder like the E6B2-CWZ6C uses terminal A8 for phase A, A10 for phase B, A12 for phase Z, and B9 / B11 / B13 for +V (encoder brown to +V, blue to common). Phase A and B feed counting and quadrature direction; Z is a configurable reset / preset / capture trigger. For RS-422 line-driver encoders, the dedicated high-speed pins on the front connector give the full 500 kHz rate. The CJ1M-CPU21 / CPU22 built-in HSC is fine for sub-100 kHz; anything faster should move to the CT021 to free the CPU for the program scan.
Before ordering
The CT021 on an NJ-series CPU drops most high-end features: pulse-rate measurement, capture values into the CIO area, and the IORD / IOWR instructions are not available. Pick a CJ1H / CJ1M / CJ2 CPU if you need those, or move to the NX-series pulse I/O for new builds. Confirm encoder type (line driver vs open-collector), count direction, and expected max frequency before ordering.
Key Features
- 2-channel high-speed counter for CJ-series Special I/O rack slot
- 500 kHz max input with RS-422 line driver, 50 kHz with open-collector
- 32-bit signed count range (-2,147,483,648 to +2,147,483,647)
- Simple / ring / linear counter modes with preset, gate, capture, reset
- 2 digital inputs + 2 NPN transistor outputs per channel
- 30 internal (soft) outputs trigger inside ladder without an output terminal
- 0.5 ms response for high-speed closed-loop control
- Up to 24 CT021 units across a CJ / NJ system
- SKU: CJ1W-CT021
- Series: CJ1W-CT021
- I/O: 500 I/O
Best-Fit Applications
- Encoder feedback for cut-to-length on extrusion and rolling lines
- Position control on rotary index tables driven by an E6B2 / E6C2 encoder
- Length / stroke measurement on linear cylinders with a tethered encoder
- RPM and line-speed measurement on rotating shafts
- Batch counting on filling, capping, and packaging lines
Buying Checklist
- Choose CJ1W-CT021 for 2 channels of high-speed counting (500 kHz line driver).
- Pick CJ1W-CT041 if you need 4 channels in one slot.
- Confirm encoder type (NPN open-collector vs PNP line driver) before ordering.
- Pair with a CJ1M-CPU21 / CPU22 or CJ2M-CPU11 / CPU35 host PLC in CX-Programmer.
- Allow up to 24 CT021 units across a single CJ / NJ PLC system.
- Pick an NJ CPU only if your application does NOT need pulse-rate or capture features.
Technical Specifications
| Unit Type | CJ-series Special I/O high-speed counter |
|---|---|
| Counter Channels | 2 independent |
| Maximum Input Frequency | 500 kHz line driver / 50 kHz open-collector |
| Count Range | 32-bit (-2,147,483,648 to +2,147,483,647) |
| Input Signal Levels | DC 5 V, 12 V, or 24 V (selectable per axis) |
| Digital Inputs | 2 per channel |
| Digital Outputs | 2 NPN transistor (sinking) per channel |
| Counter Modes | Simple, ring, linear |
| Current Draw | 280 mA at 5 VDC |
| Dimensions | 31 × 90 × 65 mm (W × H × D) |
| Weight | 100 g |
| Compatible PLCs | CJ1H, CJ1M, CJ2H, CJ2M, NJ |
Resources & Downloads
FAQ for CJ1W-CT021
What is the difference between the CJ1W-CT021 and the C200H-CT021?
The CJ1W-CT021 is the CJ-series Special I/O drop-in replacement for the C200H-CT021. Both are 2-channel 500 kHz high-speed counters with the same connector pinout, the same CX-Programmer counter-parameter map, and the same 32-bit count range. Use the CJ1W-CT021 on a CJ or CS rack; keep the C200H-CT021 only on legacy C200H Alpha or C200HS racks that are not slated for replacement.
Can the CJ1W-CT021 mount on an NJ-series PLC?
Yes, the CT021 mechanically fits and is recognised by an NJ-series CPU, but several advanced features are disabled on NJ: pulse-rate measurement, capture values into the CIO area, the external-control input capture / stop-capture-continue / stop-capture-reset-continue / capture-reset modes, the pulse-rate range control mode, and the IORD / IOWR ladder instructions. If you need those, drop back to a CJ1H / CJ1M / CJ2 CPU.
How does the CT021 connect to a 24 VDC NPN encoder like the E6B2-CWZ6C?
Terminal A8 is encoder phase A, A10 phase B, A12 phase Z. The encoder brown wire (V+) goes to terminal B9 / B11 / B13 and the encoder blue wire goes to common. Quadrature decoding is automatic: count direction follows phase A and phase B relative timing, and phase Z is the configurable reset / preset / capture trigger.
Can the CT021 replace the high-speed counter that is built into a CJ1M-CPU21 or CJ1M-CPU22?
Yes, when you exceed 100 kHz or need the linear / ring modes plus capture and preset that the CJ1M built-in HSC does not offer. The built-in HSC plus the CT021 can also run side-by-side: the built-in HSC keeps the legacy single-axis 100 kHz counter for the fast local inputs, and the CT021 takes over on a separate channel.
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