One of the many challenges faced while working with the folks at Impact Technologies LLC in Tulsa, OK was building a system to control the rotational velocity of a skid mounted pump driven by a 200 hp diesel engine.
Below is am image of the skid-mounted diesel and pump along with images of the throttle actuator and encoder feedback module.
The diesel skid shows how the diesel and pump are mounted. The diesel has a clutch that allows the engine to engage or disengage from the pump. A pully system reduces the engine speed for the pump.
The block diagram shows a simplified view of the system to aviod disclosing information proprietary to Impact. Ultimately the system is responsible for moving drilling fluid downhole. A Delta Computer Systems RMC75E motion controller is used for overall control and monitoring of the system. The output of the RMC75E controls a linear actuator which is directly connected to the throttle. Rotational feedback is provided by a BEI rotary encoder. Pressure is monitored from the output of the pump. An interface panel is connected to the RMC75E (not shown) that allows the operator to control the system.
The throttle and linear actuator are shown in the images above. The actuator is housed in the purple enclosure mounted to the side of the diesel. The actuator arm is directly connected to the throttle as shown. The travel of the actuator is controlled by a voltage signal from the RMC75E.
Bench testing of the linear actuator and RMC75E is shown above. Interface electronics for the linear actuator are in the smaller box. The RMC75E is housed in the larger enclosure which also features a touch-panel operator interface.
The BEI optical encoder that provides the feedback is shown coupled to the pump shaft by a pully system.
One of the challenges of controlling the diesel had to do with the fact that the diesel might be running, but not engaged with the pump. The control system is based on feedback from the optical encodeer attached to the pump, only if the pump is turning. A proximity switch was added to monitor the speed of the diesel by triggering on the passage of fan blades. If the fan was turning, but the optical encoder showed no pump movement, the diesel was disengaged.
By programming the RMC75E, the system was able to handle the diesel and pump interactions. If the pump was not turning, as with start-up, the controller operated in open-loop mode, allowing the operator to directly set the voltage for idle speed conditions. When the pump is engaged the controller waits for the pump to spin-up and then shifts to closed-loop control.
