Description
Key Technical Specifications
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Model Number: 9905-726
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Manufacturer: Woodward
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Supply Voltage: 20-40 VDC (low-volt); 88-131 VAC or 90-150 VDC (high-volt) selectable
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Actuator Output: 0-200 mA into 40 Ω max, forward-acting (0 mA = idle, 200 mA = full speed)
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Speed Reference Input: 1-5 VDC (or 4-20 mA via 250 Ω jumper)
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MPU Input: 1-30 V p-p, 1 kHz–25 kHz, 0.010–0.040 in. air-gap
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Load Sharing Input: 0-6 VDC from 5 A CT secondary, gain trim on board
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Droop Range: 0-10 % via 20-turn pot; isochronous when pot fully CCW
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Operating Temperature: –40 °C to +85 °C
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Power Consumption: 8 W typical, 15 W max
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Isolation: 500 V input-to-output, opto-coupled speed share line
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Mounting: 8.5″ × 2″ Euro-card, slides in 2301A chassis or DIN clips
WOODWARD 9907-147
Field Application & Problem Solved
Small gas turbines driving compressors or generators need rock-solid speed—drift 50 RPM and you trip on surge, vibration, or frequency deviation. The 9905-726 is the forward-acting workhorse of the 2301A family: 0 mA at idle, 200 mA at full speed, driving a Woodward PG-PL or TG-13 actuator on the fuel valve or steam throttle. I install it on 5 MW gas-compressor sets in pipeline stations and 3 MW cogen units in hospitals where the turbine parallels with the grid or runs island mode. Load-sharing input from a 5 A CT lets the turbine carry base-load while the utility handles swings; the droop pot sets 4-5 % so the unit doesn’t fight the grid frequency. One card replaces the mechanical governor, droop linkage, and a rack of ice-cube relays. Commissioning is straightforward: set droop to 4 %, dial null at 0 mA, bump speed until the synchroscope stops drifting. The result is stable discharge pressure, clean frequency, and no operator babysitting.
Small gas turbines driving compressors or generators need rock-solid speed—drift 50 RPM and you trip on surge, vibration, or frequency deviation. The 9905-726 is the forward-acting workhorse of the 2301A family: 0 mA at idle, 200 mA at full speed, driving a Woodward PG-PL or TG-13 actuator on the fuel valve or steam throttle. I install it on 5 MW gas-compressor sets in pipeline stations and 3 MW cogen units in hospitals where the turbine parallels with the grid or runs island mode. Load-sharing input from a 5 A CT lets the turbine carry base-load while the utility handles swings; the droop pot sets 4-5 % so the unit doesn’t fight the grid frequency. One card replaces the mechanical governor, droop linkage, and a rack of ice-cube relays. Commissioning is straightforward: set droop to 4 %, dial null at 0 mA, bump speed until the synchroscope stops drifting. The result is stable discharge pressure, clean frequency, and no operator babysitting.
Installation & Maintenance Pitfalls (Expert Tips)
MPU Air-Gap is Non-Negotiable
Gap over 0.040″ and the card loses the signal—valve snaps shut and you trip on underspeed. Gap under 0.010″ and the pickup grinds the gear teeth. I set 0.025″ cold, then verify hot; thermal growth closes the gap about 0.003″.
Gap over 0.040″ and the card loses the signal—valve snaps shut and you trip on underspeed. Gap under 0.010″ and the pickup grinds the gear teeth. I set 0.025″ cold, then verify hot; thermal growth closes the gap about 0.003″.
Droop Pot Drifts Under Vibration
The 20-turn pot loosens in 500-1000 hours of operation. After setting 4 % droop, lock the shaft with nail polish or non-hardening thread-lock. I’ve seen units drop 200 kW because the pot walked to 8 % droop overnight.
The 20-turn pot loosens in 500-1000 hours of operation. After setting 4 % droop, lock the shaft with nail polish or non-hardening thread-lock. I’ve seen units drop 200 kW because the pot walked to 8 % droop overnight.
Current Output Demands 40 Ω Exactly
Actuator coil is 38 Ω cold, 42 Ω hot—perfect match. Parallel two actuators and impedance drops to 20 Ω; the card current-limits at 220 mA and speed hunts ±5 Hz. Use separate cards or add 20 Ω series resistance.
Actuator coil is 38 Ω cold, 42 Ω hot—perfect match. Parallel two actuators and impedance drops to 20 Ω; the card current-limits at 220 mA and speed hunts ±5 Hz. Use separate cards or add 20 Ω series resistance.
Verify Speed Reference Polarity Before Start
Reverse the 1-5 V wires and the valve drives shut when you ask for 100 %. Bump demand to 10 %—actuator current should climb toward 20 mA. If it drops, swap wires at the terminal strip, not at the DCS, to keep the control loop intact.
Reverse the 1-5 V wires and the valve drives shut when you ask for 100 %. Bump demand to 10 %—actuator current should climb toward 20 mA. If it drops, swap wires at the terminal strip, not at the DCS, to keep the control loop intact.
Check Load Sharing Gain Before Paralleling
The gain trim pot sets how aggressively the unit responds to circulating current. Too high and the turbine hunts against the grid; too low and it won’t share load. Start at mid-range, parallel at 10 % load, then trim until kW splits evenly.
The gain trim pot sets how aggressively the unit responds to circulating current. Too high and the turbine hunts against the grid; too low and it won’t share load. Start at mid-range, parallel at 10 % load, then trim until kW splits evenly.
WOODWARD 9907-147
Technical Deep Dive & Overview
The 9905-726 is an analog forward-acting speed/load control on a four-layer Euro-card. A magnetic pickup zero-cross detector feeds a CD4046 phase-locked loop; the loop compares shaft frequency to an internal 60 Hz temperature-compensated crystal reference and generates a 0-200 mA error signal. Load-sharing current from a 5 A generator CT converts to 0-6 V through a precision burden resistor, sums at the PID summing junction, and applies droop via the 20-turn front-panel potentiometer. An LM336 5 V reference feeds the local speed-set pot; external 1-5 V or 4-20 mA commands can override via DIP jumper.
The 9905-726 is an analog forward-acting speed/load control on a four-layer Euro-card. A magnetic pickup zero-cross detector feeds a CD4046 phase-locked loop; the loop compares shaft frequency to an internal 60 Hz temperature-compensated crystal reference and generates a 0-200 mA error signal. Load-sharing current from a 5 A generator CT converts to 0-6 V through a precision burden resistor, sums at the PID summing junction, and applies droop via the 20-turn front-panel potentiometer. An LM336 5 V reference feeds the local speed-set pot; external 1-5 V or 4-20 mA commands can override via DIP jumper.
The output stage is a complementary NPN/PNP current source with foldback limiting—survives short circuits and reverse battery connection. The card includes 500 V opto-isolation on the speed-share line to prevent ground loops between paralleled units. No microprocessor, no firmware, no boot time—pure analog control that settles in 50 ms and survives 500 V transients, 150 °F panel temperatures, and years of vibration. The 726 revision adds thicker acrylic conformal coating and swaps carbon-composition resistors for metal-film units, improving long-term stability in H₂S and humid environments.
