A custom compatible replacement for FG4K-1200G-90G-NG must hold the 1200 PPR nickel-disk scaling, 0°/90° phase relationship, inverted signal pairs, N marker pulse, K radial terminal-box wiring, shielded twisted-pair routing, and coupling preload together; EncoderWorks configures this replacement around those limits rather than treating it as a generic incremental encoder swap. The main failure boundary is wrong speed calculation, unstable direction detection, or failed zero recovery after the pulse count, marker channel, or terminal wiring is changed. Typical production lead time: 15 working days.
This configuration belongs to the FG 4 optical incremental encoder platform for heavy-duty industrial environments. It uses 1200 pulses per revolution, square-wave output, a 0° basic channel, a second channel electrically shifted by 90°, inverted outputs for industrial signal transmission, and an N marker pulse with inverted marker signal. The K version uses a standard radial terminal box with terminal-strip wiring, not a redundant KK dual-terminal-box structure. Replacement work should focus on controller scaling, A/B phase accuracy, N marker repeatability, 100 kHz standard frequency margin, 150 kHz special-order boundary if applicable, shield bonding, cable-gland sealing, and shaft coupling alignment.
System Limits
The first system limit is 1200 PPR scaling. A controller configured for 1024, 1000, 2000, or 4096 PPR may still count clean A/B pulses, but speed, travel, and synchronization values will be wrong. Edge-counting mode, direction logic, and speed conversion should be checked before commissioning.
The second limit is phase and marker behavior. The controller must receive A with /A, B with /B, and N with /N as paired signals. If the 90° channel sequence changes, direction interpretation can reverse. If the marker-pulse polarity, wiring, or mechanical reference position changes, homing and zero return may become inconsistent.
The third limit is terminal-box EMC and mechanical load. Long exposed shield drains, loose cable glands, moisture inside the terminal box, or routing near inverter output, motor, brake, or contactor wiring can create false edges. Coupling misalignment, axial preload, radial load, or shaft shock can reduce bearing life and degrade pulse stability.
Wiring & Installation
Before replacement, record the radial terminal-box wiring for the basic channel, 90° channel, marker pulse, inverted signals, supply voltage, GND, shield, and LED-check or diagnostic output if used. Confirm that the controller scaling is set for 1200 PPR and that the installed counter has enough frequency margin for the actual shaft speed.
During installation, fit the coupling smoothly and do not strike the shaft or housing. Keep the encoder centered, control angular and parallel offset, and avoid axial preload. Route A-/A, B-/B, and N-/N through paired shielded conductors, bond the shield through the terminal box with a short low-impedance path, and keep the signal cable away from high-current wiring. After commissioning, verify pulse count, speed scaling, direction, N marker repeatability, terminal-box sealing, and signal stability through the operating speed range.
Custom Compatible Solution
EncoderWorks can configure the replacement around the installed drive and counter system:
- Match 1200 PPR square-wave incremental output with 0°/90° channel behavior and inverted signal pairs
- Preserve N marker pulse behavior, K radial terminal-box layout, supply range, output level, and controller input compatibility
- Adapt the FG 4 mechanical envelope, shaft interface, flange or foot mounting requirement, coupling alignment, and cable-gland layout
- Review 100 kHz / 150 kHz frequency margin, shielded twisted-pair routing, EMC grounding, terminal-box sealing, bearing load, and marker-pulse repeatability
Key Data
| Item | Data |
|---|---|
| Model | FG4K-1200G-90G-NG |
| Encoder type | Heavy-duty optical incremental encoder |
| Series | FG 4 |
| Connection structure | K standard radial terminal box |
| Pulses per revolution | 1200 PPR |
| Pulse disk class | Preferred nickel-disk pulse rate |
| Signal output | Square wave, 0° and 90° channels |
| Inverted signals | Yes, Option G |
| Marker pulse | Option N with inverted marker signal |
| Supply voltage | 12–30 VDC |
| Output type | Differential line driver / push-pull style output |
| Frequency range | 0–100 kHz standard, up to 150 kHz if specified |
| Standard shaft | Ø11j6 × 30 mm |
| Optional shaft | Ø14j6 × 30 mm |
| Key checks | 1200 PPR scaling, 90° phase, N marker, terminal-box shielding, coupling preload |
