Key Technical Specifications
| Parameter | Specification |
|---|---|
| Product Model | G123-825-001 |
| Manufacturer | MOOG Inc. |
| Input Signals | ±10V DC, 4-20 mA |
| Output Signals | 4-20 mA, 0-±10V, 0-±5-±100 mA (Switchable) |
| Filtering | Single-pole active filter, selectable time constant |
| Power Supply | 24V DC |
| Mounting | DIN Rail |
| Indicators | Valve Drive LED, Front Panel Test Points |
| Encoder Interface | NONE (Not Supported) |
| Software Config | NONE (No Control Builder Support) |
Product Introduction
Getting a modern PLC to talk to an older Moog valve without introducing noise is a classic headache. The G123-825-001 was built specifically for this. It sits between your PLC’s analog output and the valve, cleaning up the signal with a built-in single-pole active filter before driving the valve coil.I’ve used these to retrofit old mechanical feedback valves with modern electrical feedback units without changing the existing servo amplifiers. The switchable output options (4-20mA, ±10V, or the multi-range mA) make it incredibly versatile. But be clear on what this is not: it has zero encoder inputs and no software configuration. It’s a dumb, reliable analog buffer. If you need high-count frequency or digital tuning, this isn’t your part.
Quality SOP & Tech Pitfalls
The Lab Report:
Analog buffers are sensitive to capacitor aging. Every G123-825-001 gets a visual inspection for leaked caps or corroded test points. We then hook it up to a signal generator and scope, injecting a noisy ±10V signal to verify the filter is actually working and the output tracks correctly. We check the 24V supply rail for ripple and confirm the valve drive LED responds to input changes.The Engineer’s Warning:
Do not expect encoder feedback from this module. I’ve seen techs waste hours trying to wire up LVDTs or encoders to this, only to realize the specs clearly say “no encoder interface.” Also, check your DIP switches for the filter time constant. Leaving them in the wrong position can cause valve hunting or sluggish response. And always use the front panel test points for debugging; don’t just guess based on the LED.
Installation & Configuration Guide
- Pre-Installation: ⚠️ VERIFY SIGNAL TYPE. Confirm your PLC output is either ±10V or 4-20mA. Check the valve coil requirements and set the output DIP switches before mounting.
- Mounting: Snap the unit onto a standard DIN rail. Ensure adequate spacing for heat dissipation. Connect 24V DC power, observing polarity.
- Wiring: Connect PLC analog output to the input terminals. Wire the valve coil to the output terminals. Use shielded cable for all analog connections and ground the shield at the amplifier end only.
- Power-On & Testing: Apply 24V. The valve drive LED should illuminate when signal is present. Use a multimeter on the front panel test points to verify output voltage/current matches your PLC command. Adjust filter DIP switches if valve oscillation occurs.
Compatible Replacement Models
| Replacement Model | Compatibility | Notes |
|---|---|---|
| MOOG G123-825-001 | ✅ Drop-in Replacement | Exact hardware match. Verify DIP switch settings match old unit. |
| MOOG G123-825-A01 | ⚠️ Software Compatible | Minor revision. Functionally identical, but confirm filter options match. |
| Modern Moog EFB Amplifier | ❌ Hardware Mod Required | Requires encoder feedback wiring and software config. Not a direct swap. |
Frequently Asked Questions (FAQ)
Can I use this with an encoder feedback valve?
No. This amplifier has no encoder input circuitry. It is strictly for electrical feedback (EFB) valves or converting old mechanical feedback valves to EFB using the servo amplifier’s existing feedback loop.How do I set the filter time constant?
Use the DIP switches on the front panel. The switches add together to create different time constants. Consult the application note included with the unit for the exact switch-to-time-constant table. Start with the lowest setting and increase only if you see noise.Is this compatible with Control Builder software?
No. There is no digital communication port. All configuration is done via hardware DIP switches and trim pots. It’s purely analog.Can I hot-swap this module?
Technically yes, but I wouldn’t recommend it. The valve will likely move to a safe state or hold position depending on system design, but you risk a transient spike. Plan a brief shutdown if possible.Why is my valve hunting or oscillating?
90% of the time, it’s the filter setting being too low for your system’s noise level. Increase the filter time constant via DIP switches. If that doesn’t fix it, check your grounding and shielding. Analog signals are picky about noise.Are these actually new?
True factory-new units are extremely rare for this obsolete part. We supply New Surplus or professionally refurbished units that have been fully tested on a live valve bench. Always ask for the test report showing input/output linearity and filter verification.
