Choosing between a rotary encoder and a magnetic safety sensor might seem like comparing apples and motor shafts, but both components answer the same underlying question: what does your machine need to monitor or measure? If your control system needs to track the position of a rotating shaft, an incremental encoder gives you that feedback. If it needs to confirm that a guard door is closed before a machine runs, a magnetic safety sensor is the part designed for that job. The right choice depends entirely on your application's control-logic requirements.
Quick Verdict
If your priority is precise, low-cost feedback for a DC motor or a rotating axis, the Oak / Grigsby 91Q128 rotary encoder at $16.95 is the clear buy. It delivers 128 pulses per revolution with full quadrature output, so you get 512 state changes per revolution. If your priority is machine-safety monitoring, the Schmersal BNS 33-12ZG magnetic safety sensor at $153.00 is the component built for guarding interlock circuits, but it asks for a much bigger budget.
Comparison at a Glance
| Product | Listed Price | Best For |
|---|---|---|
| Oak / Grigsby Rotary Encoder - 128 Pulse/Rev - 91Q128 - 2 CH Full Quadrature | USD 16.95 | Position feedback on a rotating shaft with TTL logic |
| 1PC BNS 33-12ZG Schmersal Magnetic Safety Sensor ID179748 Machine Safety Control | USD 153.00 | Guard-door or interlock monitoring in machine safety circuits |
Where Each Product Wins
The Oak / Grigsby encoder wins on cost, simplicity, and adaptability. For less than twenty dollars, you get a new, sealed rotary encoder with a 1/4-inch stainless steel shaft, quadrature output, and a 4-inch cable with bare wire ends. Its 5V TTL-compatible outputs make it easy to interface with a wide range of industrial controllers, and the mounting hardware is included.
The Schmersal safety sensor wins on application focus. It is specifically positioned for machine-safety control, which means it is designed to work with interlock and guard-monitoring circuits where a wire break or misaligned actuator could create a hazard. The price, $153.00, reflects that narrow, safety-oriented role, not general-purpose sensing.
Product Notes
Oak / Grigsby Rotary Encoder - 128 Pulse/Rev - 91Q128 - 2 CH Full Quadrature
The Oak / Grigsby 91Q128 is a compact incremental encoder that gives you 128 pulses per revolution and full quadrature decoding, which translates to 512 total state changes per rev. It runs on 5V DC and outputs a 2-bit gray code, with Channel A leading Channel B by 90 degrees on clockwise rotation. That makes it a solid choice for speed or position feedback on a shaft where you have simple DC power and TTL logic available. The sealed enclosure and stainless steel shaft help it stand up to dusty or dirty environments. The bare-wire cable means you will need to plan your own connector, and because it is incremental, the controller will need to re-home after a power loss. Its combination of sealed construction, bare-wire leads, and quadrature output makes it a straightforward part to wire into a 5V logic system.
1PC BNS 33-12ZG Schmersal Magnetic Safety Sensor ID179748 Machine Safety Control
The Schmersal BNS 33-12ZG is a magnetic safety sensor intended for machine-safety control applications, where the goal is to verify that a guard or door is closed before equipment operates. It is listed as new and comes from an industrial automation supplier whose catalog covers PLCs, sensors, relays, and safety components. The product title and supplier description both emphasize machine-safety control, so this sensor is aimed squarely at interlock and guard-monitoring roles. The higher price reflects that dedicated positioning rather than general-purpose proximity detection. The description stays at a catalog level, focusing on the store's industrial automation range rather than the sensor's mechanical specifics, which is a consideration for buyers who prefer exhaustive technical documentation before they purchase.
Final Choice by Use Case
Choose the Oak / Grigsby 91Q128 encoder if you are building or repairing a motion-control axis and need low-cost, dependable rotation feedback. Choose the Schmersal BNS 33-12ZG magnetic safety sensor if you are updating a machine guard interlock and need a specific magnetic safety component, even at a significantly higher price.
