When you're outfitting a machine, two common needs can both land on your bench: you need to track how much material has rolled past, or you need to make sure a guard door is closed before the machine can run. These two components live under the same broad umbrella of sensors, encoders, and machine safety, but they serve different purposes. Here's how the 300ppr Rotary Encoder Digital Meter Counter with Wheel & Mounting Bracket and the Keyence GS-M51P Safety Interlock Switch compare.
Quick verdict
If your task is measuring rolled length and triggering equipment at a preset count, the 300ppr Rotary Encoder Digital Meter Counter is the more complete choice. If your task is monitoring a guard door or gate on automated equipment, the Keyence GS-M51P is the safety interlock switch designed for that job.
At-a-glance comparison
| Feature | 300ppr Rotary Encoder Digital Meter Counter | Keyence GS-M51P Safety Interlock Switch |
|---|---|---|
| Listed price | $86.20 | $100.00 |
| Main job | Wheel/roll length measurement | Non-contact guard door interlocking |
| Condition | New | Used |
| What's included | Meter counter, 300ppr encoder, wheel, mounting bracket | One original Keyence GS-M51P switch |
| Output | Relay output | Digital output |
| Power | 110-220V with US plug | DC |
Where each product wins
The encoder package wins when you want a whole measuring setup in one order: counter, encoder, wheel, and bracket. It's ready for roll length measuring right away. The Keyence wins when door or guard monitoring is the priority. It's an interlock switch designed for machine safety circuits.
Product notes
300ppr Rotary Encoder Digital Meter Counter with Wheel & Mounting Bracket
The strength of this package is that it arrives with everything needed for a basic length-measuring setup. Along with the 300ppr rotary encoder, you get a digital meter counter, a wheel, and a mounting bracket. The counter accepts 300 pulses per wheel revolution, and you can set an early-warning value so the controller can trigger a stop or start action. It operates on 110-220V with a US plug and is described as new. The practical limitation is that this is a measurement tool, not a safety interlock. If your application is guarding a door, this unit won't fill that role. It's best suited to roll length measurement on equipment where you need a visible count and a control output.
Keyence GS-M51P Safety Interlock Switch Non-Contact Safety Sensor
This switch is a genuine Keyence GS-M51P, removed from a working industrial automation system. It's a non-contact safety interlock switch for machine guarding, which makes it suitable for monitoring doors and guards on robotics, packaging machinery, CNC machines, and process automation. The specs show DC power and digital output. The main limitation is condition: it's used, not new. If your facility requires new components, this may not fit. But for a maintenance or repair need where a genuine replacement is acceptable, this unit gives you the interlock function without sourcing a new unit.
Final choice by use case
Choose the 300ppr Rotary Encoder Digital Meter Counter if you're setting up a length-measuring station and want the encoder, wheel, bracket, and counter in one package. Choose the Keyence GS-M51P if you need to monitor a guard door or gate on automated equipment and are comfortable with a used, genuine Keyence unit.
