Applications 

The Woodward Current to Pressure Converter (CPC) is designed for positioning steam and fuel valves and/or the associated servos. A 4–20 mA in/out signal is linearly and proportionally converted into a hydraulic output pressure. The CPC can thus interface with any electronic control, such as Woodward MicroNet™ systems and the Woodward 505 Control. It connects to pressure-operated servo systems and to single-acting power cylinders. The CPC is suited for new as well as retrofit applications.

Description 

The CPC is an electrohydraulic, pressure-regulating valve, which consists of a valve, an actuator, a pressure sensor, and on-board electronics.

The electronics perform the signal conditioning by comparing the actual output pressure with the command, which results in a reference signal for the valve position. This reference signal is then compared with the actual position, resulting in a drive signal. The driver circuit then outputs the appropriate signal to the actuator, which positions the hydraulic valve to the required position.

The valve consists of two ports; one from supply to output, and one from output to tank. By opening one of these ports, the output pressure decreases or increases. Two output signals are provided: a 4–20 mA signal, representing the actual output pressure, and a relay output, indicating a malfunction of the CPC.

Features 

The CPC has an anodized aluminum housing, coupled with a cast, anodized aluminum top cover. This enclosure contains the printed circuit board, the pressure sensor, and the actuator. The rotor of the actuator is directly coupled to the one stage hydraulic valve. The construction of the hydraulic valve in the CPC tolerates contaminant particles up to 40 µm. Upon loss of power, a return spring will force the output pressure to the drain pressure (failsafe). A brass cable gland is provided for cable access with electrical signals. The CPC mounts to a manifold with a standard instrument mounting-hole pattern according to DIN 19213.

Accessories

A standard stainless steel adapter plate (part number 4349-231), with or without close-off valves, can be supplied with the CPC. To replace the obsolete I/H converter, use adapter plate 3689-097.

Specifications 

Electrical Connections 9 screw terminals on the internal printed circuit board suitable for 0.2–4 mm² solid or 0.2–2.5 mm² stranded wire (24–12 AWG). 1.5mm² (16 AWG) is recommended for the power lines, and 0.75 mm² (18 AWG) for all other connections. Cable Entry Via cable gland—cable diameter 9–12 mm Supply Voltage 18–32 Vdc (24 Vdc nominal) Power Consumption 8 W during steady state, 120 W peak (3 seconds maximum) Current Input Signal 4–20 mA into 250 Ω Analog Output Signal 4–20 mA—maximum external load: 300 Ω. Accuracy = ±1% of full scale Discrete Output Signal Relay—jumper selectable for normally open or normally closed. Maximum rating 1 A at 30 Vdc Dither Frequency 10–30 Hz—Default setting is 30 Hz Dither Amplitude Zero is minimum and default. Maximum depends on adjusted frequency and dynamic characteristics of the entire system.

Hydraulic Connections Flat mounting face, hole pattern according to DIN 19213. Hydraulic connections via an adapter plate (optional). Supply Pressure 17 bar (250 psi) maximum. At least 0.5 bar higher than the maximum output pressure. Output Pressure Minimum level: 1 bar (14.5 psi)  Maximum level: 15 bar (217.5 psi)  Minimum range: 1 bar (14.5 psi)  Maximum range: 14 bar (203 psi) Standard Pressure Range 4–20 mA gives 1.5 to 4.5 bar (21.75 to 65.25 psi) Recommended Filter Rating Nominal 40 µm and 75 µm absolute (B40,=75) Viscosity 20 to 100 cSt Leakage Depends on viscosity and supply pressure—see figure Flow Capacity Depends on viscosity and pressure difference—see figure Technical Manuals 89543 (standard version)  26248 (explosion-proof version)

Performance Frequency response 10–30 ms time constant, small step, blocked load (no servo system attached to the CPC). Ultimate dynamic response depends on total servo system and dynamic adjustments to the CPC. Linearity 0.2% of full range Repeatability 0.1% of full range Temperature Drift 0.01% full range /°C

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