ME 360 Test #3 Spring 08 5/5/08 Closed book, closed notes portion of test. Total of 25 out of 100 points for questions #1 to #6. 1) [10] Mark the following true (T) or false (F) questions a) Pressure relief valves are used to limit the pneumatic system pressure to a preset value. b) Photoelectric sensors are used in the thru-beam, reflective, and cross-beam configurations. c) A pressure regulator attempts to maintain upstream pressure regardless of downstream pressure. d) Position, way, and port are three terms used to describe features of a valves that use sliding spools (or poppets) to direct and control fluid flow. e) A check valve allows flow in only one direction, much like a diode in electrical circuits. f) Hydraulic systems can usually use much cheaper flexible plastic tubing and fittings than pneumatic systems. g) With a PLC controlled system it is generally preferable to place at least one emergency top button outside the ladder logic, such that PLC program malfunctions cannot prevent system shutdown. h) According to the rules we use in ME360, an individual output device can appear on a ladder logic diagram as many times as needed. i) Hydraulic pumps create flow, while the rest of the system determines pressure. j) Providing two widely spaced pushbuttons for operators to start a PLC-controlled system will always provide a safe procedure. 2) [3] What does SPDT mean? Provide a sketch and a description. 3) [3] Sketch the schematic symbols and give the names for 3 different types of fluid power cylinders
4) [3] What do NPN and PNP refer to? Provide a sketch for one of them. 5) [3] In ladder logic, what is a hold circuit and what is it used for? What are the important considerations in designing a hold circuit? 6) [3] Identify the following fluid power and electrical schematic symbols use most complete label.
ME 360 Test #3 Spring 08 5/5/08 Closed book, one open note page (student-prepared) portion of test. 7) [15] A complete pneumatic and ladder logic system is shown below. Fully describe the operation of this system both in terms of ladder logic components (,,, etc.) and in terms of the actions of the three cylinders. Cyl A X0 Cyl B X21 Cyl C X30 X21 X30 CTR6 CT6 C3 T5 C3 C3 +24VDC Inputs Outputs +24VDC TMR T5 K25 X21 X30 CT6 CT6 X30 CNTR CT6 K3 X0
8) [6] Estimate the pressures P1, P2, and P3 while the load in the figure below is moving up slowly. P1 = P2 = P3 = 100 feet of tubing P2 8000 lb P1 d rod =1.50 in Set @ 2000 psi P3 Set @ 900 psi d piston =3.50 in 9) [6] Estimate the pressures P1, P2, and P3 while the load in the figure above is moving down slowly. P1 = P2 = P3 = 10) [3] Identify the component on the right and describe its operation. 11) [3] Identify the component on the right and describe its operation. 12) [3] Identify the components on the right and describe the operation. 13) [3] Identify the component on the right and describe its operation.
14) [36] A local pipe manufacturer has a need for a pneumatic system controlled by a PLC. The system is used to sort pipes by diameter. Two sizes of pipe travel on a conveyor: large and small. The conveyor belt is operated by a motor which is turned on when the PLC output Y0 is on. The conveyor belt is started by an operator pressing the Start button (wired NO to X0) and can be stopped at any time by pressing the Stop button (wired NO to X1). Large pipes are detected by a proximity sensor wired NO to X2. The conveyor belt must stop when a large pipe is detected. after a 2.0 second delay to allow the conveyor to stop, the large pipe is pushed off the conveyor belt by a double acting, single ended cylinder A cylinder A is controlled by a 2 position, 4 port, solenoid actuated (wired to ), spring return, directional control valve retracted and extended positions of cylinder A are indicated by limit switches wired NO to inputs X3 and X4 respectively. The conveyor belt motor should re-start automatically after the cylinder for pushing the large pipes is fully retracted Small pipes are detected by a proximity sensor wired NO to X5. The conveyor belt should stop when a small pipe is detected. no delay is required, but the small pipe is pushed off the conveyor belt by extending and retracting a double acting, single ended cylinder B two times for each small pipe cylinder B is controlled by a 2 position, 4 port, solenoid actuated (wired to Y5), spring return, directional control valve retracted and extended positions of cylinder B are indicated by limit switches wired NO to inputs X6 and X7 respectively. The conveyor belt motor should re-start automatically after the small cylinder is fully retracted the second time. Your problem: a) Draw a PLC wiring diagram for the limit switches and solenoids wired as indicated above, b) Design a PLC ladder logic diagram to control the system. Be sure to provide a brief description beside each rung of the ladder to describe what you are trying to accomplish. Cylinder A Cylinder B X3 X4 X6 X7 Y5