Key Technical Specifications
| Parameter | Specification |
|---|---|
| Product Type | Current-to-Pressure (CPC/I-P) Converter |
| Input Signal | 4-20 mA |
| Output Pressure | 3-15 psi (proportional) |
| Accuracy | ±0.1% of full scale |
| Supply Voltage | 24 VDC |
| Zero Adjustment | ±10% of full scale |
| Span Adjustment | ±10% of full scale |
| Response Time | <10 ms |
| Operating Temperature | -40°C to +85°C |
| Typical Application | Turbine fuel/steam valve positioning, actuator pilot control, retrofits |
Product Introduction
I’ve replaced enough I/P converters on turbine skids to know this: when the CPC drifts, the whole control loop lies to you. The Woodward 8701-758 / 5601-1126 is one of those unglamorous devices that sits between a 505, MicroNet, or similar controller and the hydraulic pilot stage — and when it fails, operators see valve position errors, hunting, or sluggish load response before anyone thinks to check the converter.This is not a controller. It is not a governor. It is a transducer. Its job is simple — take 4-20 mA and make a clean, repeatable 3-15 psi output — but “simple” does not mean forgiving. The ±0.1% FS accuracy spec is tight for a field instrument, and the <10 ms response means it can keep up with fast-acting turbine control loops. The -40°C to +85°C temperature range tells you Woodward intended this for real plant environments, not climate-controlled labs. Just don’t assume every unit labeled 8701-758 ships calibrated to your exact output range.
Quality SOP & Tech Pitfalls
The Lab Report (SOP):
- Visual and counterfeit check — label, part numbers 8701-758 and 5601-1126, connector condition, housing integrity.
- Pneumatic port inspection — verify no debris, cracked fittings, or damaged threads.
- Bench calibration check — apply 4-20 mA from a calibrated source and measure output pressure at 4, 8, 12, 16, and 20 mA.
- Linearity and hysteresis verification — ramp up and down to catch sticky internal mechanisms.
- Supply voltage test — confirm stable operation at 24 VDC.
- Response time spot check — verify output tracks input changes without excessive lag.
- Anti-static bag, foam, and sealed carton.
The Engineer’s Warning (Pitfalls):
The most common mistake I see is swapping a CPC without verifying the output pressure range. Not every Woodward CPC is 3-15 psi. Some are 0-15 psi, 0-30 psi, or application-specific ranges. Install the wrong range and your valve will either never reach full travel or slam open at mid-scale current.Second: moisture. These converters live near hydraulic power units and steam lines. If the air supply is wet or dirty, the internal nozzle-flapper or piezo mechanism fouls quickly. Always check the instrument air quality before blaming the converter for drift.
Installation & Configuration Guide
1. Pre-Installation ⚠️
- Isolate the control loop and place the turbine or actuator in a safe state.
- Confirm the replacement output pressure range matches the original unit’s tag.
- Photograph the existing wiring, tubing, and mounting orientation.
- Verify clean, dry instrument air supply at the required pressure.
2. Removal
- Depressurize the pneumatic output line before disconnecting tubing.
- Label the 4-20 mA wiring and 24 VDC supply leads.
- Disconnect pneumatic tubing carefully — cap open ports immediately.
- Remove mounting hardware and extract the converter.
3. Installation
- Mount the replacement in the same orientation as the original.
- Connect pneumatic tubing with clean, leak-free fittings.
- Wire the 4-20 mA input and 24 VDC supply per the OEM diagram.
- Verify polarity — reversed current input will give reversed or no output.
4. Power-On & Testing
- Apply 24 VDC and verify the unit powers up.
- Inject 4 mA and confirm the output reads approximately 3 psi (or the calibrated zero).
- Step through 8, 12, 16, and 20 mA and verify proportional pressure output.
- Check for hysteresis by ramping back down to 4 mA.
- Verify no air leaks at fittings and that the control loop responds correctly.
- Document the as-found and as-left calibration values.
Compatible Replacement Models
| Model | Compatibility | Notes |
|---|---|---|
| WOODWARD 8701-758 / 5601-1126 | ✅ Drop-in replacement | Same CPC; verify output range and calibration tag. |
| WOODWARD CPC series (other part numbers) | ⚠️ Functionally compatible | May require recalibration, different mounting, or revised tubing. |
| Third-party I/P converters (4-20 mA to 3-15 psi) | ⚠️ Application-dependent | Must match output range, response time, and environmental rating. |
Frequently Asked Questions (FAQ)
Is this a governor or controller?
No. It is a current-to-pressure transducer. It converts a 4-20 mA signal into a pneumatic output. The governor or controller lives upstream and sends the current signal.Can I substitute any Woodward CPC for this one?
Not automatically. Woodward CPCs come in different output ranges and calibrations. A unit labeled 8701-758 may still be calibrated for a specific application. Always compare the output pressure range on the nameplate.What happens if the output range is wrong?
The valve will not position correctly. A 0-30 psi CPC in place of a 3-15 psi unit will over-travel the actuator. A 0-15 psi unit in place of a 3-15 psi unit will leave the valve slightly open at zero signal. Neither scenario is acceptable on a turbine.Does it need clean instrument air?
Yes. Contaminated or wet air is the fastest way to kill an I/P converter. Use a proper filter-regulator-lubricator setup if the application calls for it, and keep the air supply dry.Can I calibrate this in the field?
Yes — the zero and span adjustments allow ±10% FS trim. But if the unit is severely out of calibration or shows hysteresis, bench calibration or replacement is the better call.What condition are these units in?
Stock is typically new surplus or verified surplus. Each unit is visually inspected and functionally checked where possible. If you need a specific calibration certificate or as-left data, request it before ordering.Is the 10 ms response time guaranteed on every unit?
That figure comes from available third-party specifications. Actual response depends on supply pressure, tubing length, and load volume. Treat 10 ms as a reference value and verify on your bench if your loop dynamics are tight.
