Massachusetts Amusement Device Safety Seminar 2015

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1 Massachusetts Amusement Device Safety Seminar 2015

2 MANUAL RELAY LOGIC RELAY LOGIC WITH PLC MONITORING PLC CONTROLLED DUAL PLC CONTOLS MULTI REDUNDANT PLC CONTROLLED

3 Included on the handout CD 828 Pages

4 Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch.

5 It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most recent rev olution, the Programmable Logic Controller (PLC). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls.

6 PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come. Most of this is because of the advantages they offer.

7 Cost effective for controlling complex systems. Flexible and can be reapplied to control other systems quickly and easily. Computational abilities allow more sophisticated control. Trouble shooting aids make programming easier and reduce downtime. Reliable components make these likely to operate for years before failure.

8 Ladder logic is the main programming method used for PLCs. As mentioned before, ladder logic has been developed to mimic relay logic. The decision to use the relay logic diagrams was a strategic one. By selecting ladder logic as the main programming method, the amount of retraining needed for engineers and trades people was greatly reduced.

9 Modern control systems still include relays, but these are rarely used for logic. A relay is a simple device that uses a magnetic field to control a switch, as pictured in Figure 2.1.

10 When a voltage is applied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch.

11 The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized.

12 Relays are normally drawn in schematic form using a circle to represent the input coil. The output contacts are shown with two parallel lines.

13 Normally open contacts are shown as two lines, and will be open (nonconducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting).

18 A sensor is any of various devices designed to detect, measure or record physical phenomena, including: radiation heat pressure presence, etc. and to respond by transmitting information, initiating changes, or operating controls.

19 In amusement rides, sensors are essential in providing positioning data so controllers, like PLCs, can perform their functions. In safety, sensors used in safety interlocks and guards protect people from hazards. They also aid in manual functions and processes to make them easier and more accurate.

20 In any automated application, sensors close the data loop between the operator, the controller, and the process or operation. There are two (2) general types of sensing: Discrete (on-off) & Analog (continuous-proportional)

21 Discrete type answers the question, Is it here, or not? Discrete sensors have a contact. The ON-OFF position corresponds to the discrete sensors state. Used where target must be in a definite location for operation.

22 Analog type answers the question, Where is it? Analog gives a continuous response. Analog responds best to continuous processes, such as level control, positioning, etc.

23 Nominal sensing distance: The rated operating distance for which the switch is designed. Usable sensing distance: This sensing distance is used for specifying a specific sensor for an application. Effective sensing distance: This is the actual sensing distance realized by the actual application. Standard target: An object with standardized dimensions, used in the laboratory to determine performance. Target: The real object to be sensed.

25 Presence sensors detect the presence of an object or target. There are two (2) general categories of presence sensors: Physical contact (example: limit switches) & Noncontact (example: photoelectric sensor)

26 Limit switches have activation through physical contact with the target. Noncontact sensors sense the target but do not contact or touch it. They are usually solid-state devices.

27 Carry more current. Are safer -- when opened there is an air gap between the contact terminals.

28 Reed Relay (Magnetic Target) Inductive (Metal Target) Capacitive (All Materials Target) Photoelectric (All Materials Target) Others Ultrasonic (All Materials Target) Magnetic Reluctance (Magnetic Metals Only) Hall Effect (Magnetic Target)

29 Physical contact is not required. No moving parts to jam, fail, or be broken. Faster. No bouncing at contact state change.

30 Advantages Disadvantages Applications Inexpensive: very selective target identification. Magnet required. Security and safety interlocking. Sensitive to welding fields. Sensing through metal.

32 Advantages Disadvantages Applications Complete switching function in circuit. Operates up to 150kHz. High temperature (150 Degrees C) Good resolution. Magnetic target only. Extremely sensitive to industrial environment. Security and safety interlocking.

33 Advantages Disadvantages Applications Senses all materials. Resolution. Repeatability; sensitive to background and environment changes. Anti-collision on AGV (automated guided vehicles). Doors.

34 Advantages Disadvantages Applications Resistant to harsh environments. Easy to install; very predictable. Distance limitation to 60 mm. Presence detection on all kinds of machines and installations.

36 Advantages Disadvantages Applications Senses all materials. Detects through walls. Very sensitive to environment changes. Level sensing with liquids and non-metallic parts.

38 Advantages Disadvantages Applications Senses all materials. Longest sensing range. Versatile. Subject to contamination. Parts detection. Material handling. Packaging.

43 An enclosure is a case built to provide protection to personnel from contact with enclosed equipment, and to protect the equipment from the environment. American standards are by NEMA. European standards are by IEC.

46 The more control you have over what passes in front of the sensor, the better. The less control you have over what passes in front of the sensor, the more selective the sensor must be for identifying the target. Repeatability is the ability of a specific sensor to repeatedly detect a target at a given point. It is related to the precision needed for the application.

47 Look for the different types of sensors. Look at how they are used. Understand their use in the control system for the ride. Understand the ways to use the sensors in the testing and inspection of the ride. Refer to the handouts if needed.

48 Check with sensor manufacturers. Check with the ride manufacturers. Check the internet (World Wide Web). Check with the park s sensor supplier.

49 MOTORS, STARTERS, & VARIABLE FREQUENCY DRIVES

50 Theory DC Motors, Starters, Drives AC Motors, Starters, Drives Application AC Drive Selection, Installation, & Setup

51 Advantages: variable speed high torque at any speed well established in industry Disadvantages: complexity high cost high maintenance DC power required

52 Applications cranes, hoists (start slowly, accelerate quickly) steel mills robotics rides Any place where variable speed and high starting torque are required

53 Construction Armature coil windings iron cylinder w/slots commutator shaft Field Windings (series & shunt) Series - few turns, large wire, in series w/armature Shunt - many turns, small wire, parallel w/armature

54 Construction (cont d) Case brushes bearings body (frame) frame yoke

56 3 Types of DC motors Series - high starting torque, poor speed regulation - not controllable (car starter motor) Shunt - good low speed torque - easily controllable Compound - both sets of field windings, best of both worlds - more expensive

58 Direction of rotation Direction changes when armature and field polarity change relative to each other. Because of internal connections, simply reversing the supply wires will not reverse direction of rotation.

59 Standard connections for DC motors To make motor operation predictable, a standard terminal labeling was established

60 Field Current Relay (FCR) In a compound motor, if the shunt winding fails, the motor will increase speed, possibly beyond safe limits. We need a way to remove armature current if the shunt winding is not operating. The field current relay does this.

61 Across the line starter a simple, high-current switch requires 2-wire DC supply speed/torque/current not adjustable double contacts to reduce arcing overload device on + terminal holding relay & E-stop should include FCR

63 Across the line starter (cont d) Advantages lowest cost simplicity - 2-wire control rugged/low maintenance Disadvantages maximum startup current speed/torque/current not adjustable

64 Definite Time Starting Used to reduce startup current/torque Operation Add one or more resistors to armature circuit Time delay switch(es) shunt out resistor(s) when motor/system gets up to speed

65 Time Delay Starter with Resistors

66 DC Drive Used to vary speed/torque/current to DC motor Operation 3-phase AC power is phase-shift rectified to produce a variable voltage output to armature Field current is independent, low-power DC, usually a fixed value Decreasing field current allows speeds above rated At constant hp, torque decreases as speed increases

68 DC Drive (cont d) Built-in current limiting is no substitute for fuses or overload protection Speed can be regulated with varying loads Tachometer or encoder feedback used to close loop Drive output is adjusted to keep speed constant

69 Purpose Most commonly used for fixed-speed, one direction Blowers, fans, mixers, conveyors, etc. Peak torque occurs at approx. 60% of rated speed Speed difficult to control until the advent of drives Allows high torque at low speeds Much more prolific than DC motors (large hp)

70 Construction Usually simpler in construction and less expensive than DC motors - for a given task Can be 1, 2, or 3-phase Components Rotor (analogous to armature in DC motor) copper or aluminum bars in slots in rotor, connected at each end by continuous ring (squirrel cage) no commutator, only bearings - low maintenance

71 Construction (cont d) Stator (analogous to field winding) 3 windings in 3-phase motor Power is applied to stator - none to rotor Case (frame) holds bearings, yoke, mounts very heavy to handle torque

72 Case Stato r Rotor

73 Operation transformer action induces current from stator into rotor 3 phases of field in stator rotate at AC power frequency around rotor motor speed is AC frequency divided by # of pole pairs in stator ex. - 4 poles (2 pairs) run at 3600/2 = 1800 rpm (theoretical no-load speed)

74 Operation (cont d) interaction of stator/rotor fields creates torque torque is greatest at zero rpm no torque at synchronous speed (1800 rpm -> 1750 rpm rated, no-load) Slip is the difference between stator field rotation and rotor speed increase in slip increases torque, decreases efficiency

75 Operation (cont d) Direction of rotation can be reversed only by swapping exactly two of the 3 input phases if a ride is running backward after hookup - just swap any two of its power leads As with a DC motor, startup currents and torques can be % of normal full-load for large motors, the line transients may exceed local electrical code excessive torques can be bad for equipment/riders

76 600 % Current and % Torque Torque Break down torque (peak Torque) Rated Torque at rated FLA. Synchronous speed 0 Speed (RPM)

77 To reduce excessive startup torques/currents we use starters or drives Starters are switches that can be used alone (across the line) or with currentlimiting devices (resistors, autotransformers, etc.) Starters are on/off, hi/low, forward/reverse Drives can vary the speed, torque, direction, and current - continuously variable

78 Drives usually incorporate safety features such as current monitoring Drives can be used for closed-loop control But enough about drives - we ll get to them soon!

79 Typical starting methods include: Full voltage (across the line) Just like a wall switch - no reduced current! Resistance Series resistance to stator is shorted when motor is up to speed Autotransformer like the resistor it provides reduced voltage until bypassed - usually under timer control

80 Starting Methods (cont d) Impedance uses a reactor (coil/core) instead of resistor Star-delta requires motor with individual connections for each lead of each winding switch connects windings in Star configuration for starting (low current) and Delta configuration for running (high current)

82 Star or Wye (low current) Delta (high current)

83 To accurately control speed or torque we must use a drive AC drives are much more complex than DC drives The input 3-phase power is rectified to DC The DC is then turned back into AC at the desired frequency and amplitude (inverter) The frequency controls speed and the amplitude varies torque - but there is some overlap

84 3 Ph AC 3 Ph AC DC Regulators, logic control, and bridge firing Regulators, logic control, and bridge firing AC Arm Field Inverter Torque Current Flux Current Torque & Flux Current ARM DC Field

89 Reflected Waves Large spikes on cable between drive and motor Caused by high frequency/fast rise time PWM waveform Creates corona in motor coils Corona breaks down insulation and causes arcing Corona often manifests itself as motor overload

91 What can you do about it? Specify and buy inverter duty insulated motors Keep motor lead lengths as short as possible Install a motor protection device where needed

92 Output Reactor between drive & motor Slopes off the waveform (lengthens rise time) Reduces destructive force for same amplitude Allows longer lead lengths Does create Voltage drop May cause reduction in torque

93 Terminator Highly Cost Effective Smaller No Voltage Drop any cable distance Maintains current waveform 2 choices fit all applications Most effective solution Works on all A-B IGBT & BJT drives

94 Allen-Bradley 1329 Inverter Duty Motor AC Motor AC Drive 1204-RWR2 Reactor KLC or Non Inverter Duty Motor AC Motor Terminator 1204-TFA1

95 Plot 2 Before and after the addition of a 1204-RWR2 & 3.0mhy output reactor HP 460V 60HZ No-load 300ft shielded cable After addition of 1321 output reactor Motor 14 s/rise time After addition of 1204-RWR2 Motor Inverter Before addition of 1204-RWR2 Motor Inverter

96 Electrical Noise Created by fast rise times and high frequencies Can affect communications May also affect other systems nearby Can be reduced via several methods Filtering Proper grounding reduce frequency and rise time

97 L1 L2 A B C Inverter output voltage V LL MOTOR WINDINGS E PE PE L3 Corruptive Current LOGIC L-Interface C CABLE STRAY L INTERFACE C SLOT BOND TO PE GROUND Building Ground Grid or Structure Steel PE GROUND BUS POTENTIAL #1 POTENTIAL #4 INTERFACE - PLC - ANALOG OUT - RIO - etc. Common Mode Current POTENTIAL #2 POTENTIAL #3

98 A B MOTOR C C STRAY CHASSIS GROUND BASE DRIVER BD TO IGBT P.S. +/- P.S. FRAME GROUND SHIELD OPTION LOCAL GROUND 40 KHz CONTROL BOARD CHASSIS/FRAME GROUND 100 KHz SWITCHER ISO ISO COM E +5v DCOM +12v OR +5v DCOM SCAN HIM PMT TO DCOM PE SHIELD PE #1 PE #2 PE REFERENCE PLANE

ECET 211 Electrical Machines and Controls

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