In the sensors, encoders, and machine safety world, a rotary encoder choice usually comes down to one question: what output signal does your control system expect? The Oak / Grigsby 91Q128 is a compact incremental encoder, while the RCH20D-2000 replacement is an industrial optical unit. One is built for small logic boards and instruments; the other is built for larger automation systems.
Quick Verdict
If your project is a low-cost position sensing build, go with the Oak / Grigsby 91Q128. If your machine needs industrial-grade feedback, go with the RCH20D-2000 replacement.
Comparison Table
| Feature | Oak / Grigsby 91Q128 | RCH20D-2000 Replacement |
|---|---|---|
| Price | $16.95 | $249.61 |
| Resolution | 128 pulses/rev | 2000 P/R |
| Output | 2-bit gray code, full quadrature | Line driver - voltage control |
| Shaft | 1/4-inch diameter, 0.4-inch long, stainless steel | 8mm hollow shaft |
Where Each Wins
The Oak / Grigsby wins for simplicity and included mounting hardware. The RCH20D replacement wins for output robustness and a direct shaft-mounted form factor.
Product Notes
Oak / Grigsby 91Q128
This encoder is a sensible pick when you want a low-cost quadrature signal for a 5V TTL circuit. The $16.95 price is the easiest reason to reach for it, and the included nut and star lock washer get you ready to mount on a 1/4-inch shaft. The sealed enclosure and stainless steel shaft add durability without adding weight, and the 4-inch cable has bare wire ends so you will need to supply your own connector or solder the leads directly. It is ideal for panel meters, manual adjustment knobs, and other low-speed sensing tasks where a simple position signal is enough.
Rotary Encoder Replacement for RCH20D-2000/3-8MM-5/0-LD/VC-1-M6-S Industrial
This replacement is aimed at an RCH20D series application with an 8mm shaft. It is a new unit made to replace the RCH20D-2000 model. The line driver - voltage control output is the big advantage: it gives industrial controllers a balanced signal that handles noise and long cable runs much better than a single-ended quadrature output. The hollow-shaft optical design also means you can slide it over a shaft without adding a coupling. The limitation is the price: at $249.61, it costs significantly more than the $16.95 Oak / Grigsby, so you want to be sure your machine actually requires this level of output.
Final Choice by Use Case
For 5V logic experiments, low-cost position indicators, and manual controls, the Oak / Grigsby 91Q128 is the pragmatic match. For industrial automation and machine feedback, the RCH20D-2000 replacement is the specification you likely need. Match the encoder's output format to what your control system expects.
