Product Description:

The VT-VRPA1-51-11 is an analog proportional amplifier card built by Bosch Rexroth Indramat for the VT-VRPA Electric Amplifiers series. Designed as a master card, it mounts in a 19-inch Eurocard rack and conditions command signals for hydraulic proportional valves. Within an automation cell, the card converts low-level current or voltage references into controlled solenoid power so that the valve spool position follows the process setpoint.

The card operates from a supply of 24 V DC, and an internal regulator provides ±9 V reference rails for signal conditioning. A bias current of 400 mA is available at the output stage to preload the valve and trim null drift. During full actuation, the amplifier delivers a solenoid current of 1.2 A, matched to a coil resistance of 12.7 Ω so thermal limits are not exceeded. The current input path presents 100 Ω of resistance, allowing a 4–20 mA command source to drive the card without a significant burden. To minimize static friction in the hydraulic valve, the power stage imposes a dither at 300 Hz. This high-frequency modulation keeps the spool moving slightly and improves proportional response.

Timing for the dither and ramp functions is derived from an internal oscillator running at 2.5 kHz, which also supports the analog pulse-width modulation method used by the power driver. The Eurocard footprint measures 100 × 160 mm, and the front panel height of 128.4 mm aligns with DIN subracks. The component side occupies a width of 3 TE, while solder joints project only 5.08 mm on the opposite face to provide clearance. Field installation uses a 32-pin male DIN 41612 Form D connector that carries power, input signals, and solenoid lines. Overcurrent protection is provided by an onboard slow-blow fuse rated at 2.5 A T, preventing damage if a short circuit develops in the valve circuit or wiring.