Egham, England--Start with a stepping motor-controlled screw pump. Add a pressure transducer and microprocessor. Then develop some simple control algorithms. This is how GDS Instruments transforms an ordinary hydraulic pump into a precise regulator of pressures as high as 150 Mpa (22,000 psi).
To work, the stepping motor and gearbox turn a ball screw through a captive ball nut. This action displaces the piston inside its cylinder. The transducer, which measures fluid pressure in the cylinder, informs the control circuit of the pressure changes. Finally, the control circuit and microprocessor instruct the motor to step forward or back to maintain target pressure.
Bruce Menzies, director of GDS, explains that the system can be programmed through a built-in control panel to ramp and cycle pressure linearly with respect to time. Additionally, the device offers a computer interface to accommodate a PC. Users, therefore, can input their own custom programs.
Such functions, says Menzies, not only apply to pressure, but to volume change as well. For example, he points out that with 200 steps/revolution of the stepping motor, a 25:1 reduction gearbox, and a 5 mm pitch on the precision ground screw, "it is a simple procedure to size the cylinder bore so that one step of the motor equals a volume change of one cubic centimeter."
Because of its ability to regulate volume change, the system allows precise dosing. Other possibilities include switching between two systems and a reservoir for unlimited flow, and using external transducers such as load cells, displacement sensors, and differential pressure sensors for closed-loop control of piston movement.
Additional details...Contact Bruce Menzies, GDS Instruments Ltd., Unit 12 Eversley Way, Thorpe Industrial Estate, Egham, Surrey, England TW20 8RG, Tel: +44 1784 439228, FAX: +44 1784 434644.
SIZE: 860 mm ◊ 230 mm ◊ 220mm
WEIGHT: FROM 20 kg
PRESSURE RANGES: 2, 3, 7, 10, 20, 32, 64, 150 Mpa
COMPUTER INTERFACE: IEEE-488 STANDARD AND RS 232
VOLUME CHANGE ACCURACY: 0.25% MEASURED VALUE
VOLUME CHANGE RESOLUTION: 1.0 cu-mm
PRESSURE MEASUREMENT ACCURACY: 0.1% FULL RANGE
PRESSURE MEASUREMENT RESOLUTION: +- 1 IN 10,000
Control of ultra-high pressure in hydraulically operated test systems
Computer-controlled dosing in industrial chemical processes
Control of small pressure differences at high line pressures