On-board electronics (OBE) is the direct and best way to correct nonlinear behavior of a valve, according to officials at Argo-Hytos, Zug, Switzerland. Direct-acting proportional control valves with integrated digital OBE allows fine control of valve spool position and movement. Incorporating a sensor and electronics into the valve body enables a control loop within the system, so mechanical tolerances, friction and wear no longer lead to inaccuracies and failures in the drive movement. And for systems that require machine monitoring, sensor information can also be sent directly to the main controller.
Valve opening and resulting flow rate can be modulated continuously in proportion to a reference signal. Advantages of implementing proportional technology in hydraulic applications include higher efficiency and accuracy, faster response time, low hysteresis, better repeatability and the ability to adapt the control to best suit the needs of the user. As such, Argo-Hytos valves combined with advanced OBE are capable of meeting the demands posed by a large variety of stationary and mobile applications.
The company’s new PRM9 directional control valves combine OBE with a robust design, letting its customers take full advantage of the benefits of proportional technology. The PRM9 proportional valve consists of a cast-iron housing, a special control spool, two centering springs with supporting washers, one or two proportional solenoids, a position sensor and digital onboard electronics.
The measurement system of the position sensor is based on a differential transformer with a sensor core and an electronic evaluation unit. The unit, containing the digital onboard electronics, mounts on the valve housing. Thus, solenoids connect directly to the electronics without any cabling. A cable connects the position sensor to the control unit.
The digital control unit uses pulse-width-modulation (PWM) and supplies the solenoids with current proportional to the control signal. Supply current is additionally modulated with a dither frequency and an amplitude. Individual functional parameters like ramp, offset, deadband, maximum current and so on, can be adjusted with PRM9 parametrization software. A standard computer can connect to the valve via a USB.
Each valve is individually configured at the factory, and the configuration data file, parametrization software and fieldbus data file can be downloaded from the Argo-Hytos website. Users can also individually adjust the electronics settings via the parametrization software.
Various options include internal spool position and external feedback, and CANopen and fieldbus connectivity. All models are equipped with LED optical feedback: flash codes of the three LEDs indicate valve status. Rugged construction ensures excellent shock and vibration resistance, and the valve complies with EMC, IP, and environmental climate and temperature demands. In the standard version, the valve housing is phosphated and steel parts are zinc-coat protected according to ISO 9227. Enhanced surface protection (ISO 9227, 520 hr salt spray) for mobile applications is available.
The proportional directional valves currently come in two sizes. PRM9-06 Size 06 (D03) is rated for maximum flow of 30 l/min (8 gpm) and a maximum pressure of 350 bar (5,100 psi). The PRM9-10 Size 10 (D05) has a maximum flow of 60 l/min (16 gpm), also with a maximum pressure rating of 350 bar. They’re typically used for position and speed control of hydraulic actuators