EncoderWorks develops a concise custom compatible solution for FGH4K-500G-90G-NG/20P, focused on preserving 500 PPR incremental hollow-shaft feedback while keeping the 20P shaft fit, torque bracket movement, NG reference pulse, and shield grounding stable. The replacement fails when the controller scaling is correct, but the hollow-shaft encoder is mechanically preloaded or the reference channel is not restored with the same installation behavior. Typical production lead time: 15 working days.
Where the System Fails First
The controller reads FGH4K-500G-90G-NG/20P as an incremental hollow-shaft encoder with A/B square-wave channels shifted by 90° and an NG reference pulse with inverted signal. The FGH 40 manual lists 500 PPR as a standard pulse rate. For square-wave pulse versions, the output stage is a current-limited, short-circuit-proof push-pull line driver, with 12–30 VDC supply and 200 kHz maximum frequency unless otherwise specified.
This replacement fails when 500 PPR is considered low-risk and the mechanical side is ignored. At this pulse count, counter bandwidth is usually not the first problem. The real field risk is a preloaded torque bracket, poor shaft alignment, weak shield contact, or an NG reference signal that is not checked during slow rotation.
A stable replacement must first reproduce the original 500 PPR scaling, A/B phase order, NG reference behavior, and free torque bracket movement before the encoder can be accepted.
Hollow-Shaft and Mechanical Boundary
The /20P structure indicates a 20 mm hollow shaft with feather key. The manual specifically warns not to use a hammer during installation because bearing or coupling damage can occur. It also requires careful adapter-shaft alignment, with maximum radial runout of 0.05 mm, and states that the link rod must rotate easily around the link rod heads to avoid bearing damage.
For FGH4K-500G-90G-NG/20P, the unique checkpoint is mechanical freedom rather than high pulse frequency. If the bracket is used to pull the encoder into alignment, the output may remain electrically clean at first, but bearing stress, vibration, or reference instability can appear later under load.
Installation Notes
- Set the controller counter value before startup
- Check A/B phase order against actual shaft rotation
- Test the NG reference pulse at low speed
- Mount the hollow shaft without hammer impact
- Keep the torque bracket and link rod free from preload
- Tighten cable glands and terminal-box entries before operation
- Keep shield bonding short, continuous, and low-resistance
- Route signal cables away from inverter and motor power wiring
Key Data
- Model: FGH4K-500G-90G-NG/20P
- Type: Incremental hollow-shaft encoder
- Pulse rate: 500 PPR
- Signal format: G, 90° A/B square-wave
- Reference pulse: NG, with inverted signal
- Supply voltage: 12–30 VDC
- Output: Push-pull line driver
- Max frequency: 200 kHz
- Hollow shaft: 20P
- Protection: IP65 standard
- Standard temperature: 0°C to +70°C
- Main replacement focus: torque bracket freedom, low-count scaling, NG reference pulse, hollow-shaft alignment
