plc final
the type of relay used for an application depends on the life expectancy, electrical requirements, and cost requirements of the application. electromechanical relays are typically rated for 250,000 operations, and solid state relays can be rated for billions of operations.
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there are two methods of entering analog input and output addresses into a PID instruction. In the first method, the address of the analog input terminal and the address of the analog output terminal are entered directly into the PID instruction as a process variable and control variable , respectively.
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A reset instruction is required to reset an RTO instruction.
true
An overvoltage occurs when there is more than a 10% increase in voltage for longer than one minute.
true
Analog sensors are used to send signals that represent a changing pressure, temperature, or fluid level to a PLC.
true
Both the input terminals and output terminals can be forced ON or OFF using programming software.
true
CPUs are rated according to the size of the program memory and scan time.
true
Digital circuits turn loads fully on or fully off.
true
EEPROM is used in PLCs to provide power failure backup for the RAM memory.
true
Pushbuttons, selector switches, limit switches, and proximity switches are common input devices.
true
The CPU is the section of the PLC that houses the processor (brain) of the PLC.
true
lesson1 q 23
visual
What is the third step in the OSHA lockout/tagout procedure?
Isolate machinery or equipment.
Run mode- is a plc state of operation where the operating cycle of the plc is running continuously to control a machine or process
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a program check is a check that verifies that a plc program functions properly without the application or process the plc controls actually being run.
book
all Dc voltage sources have a posititve and negative terminal. the positive and negative terminals establish polarity in a circuit. polarity is the positive or negative state of an object. Dc positive polarity is also called the source or supply
book
input devices can be programmed in series parallel or in combinations
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nested branches cannot overlap
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program mode - is a plc state of operation where the operating cycle of the plc is not running but the cpu is reay to accept information
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regardless of the size or type of plc installation, a pc with an interface cable is required for programming. laptops are very popular for programming plcs because laptops can be taken to the location of a plc installation.
book
the PID instruction has a selection that allows the technician to access the PID setup screen. the setup screen allows the technician to adjust numerous parameters related to the PID instruction to optimize analog control.
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the control instructions for output components are placed to the right on a rung. each rung must contain at least one output component control instruction. most rungs contain both condition and control instructions.
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the first check that a technician should perform is to verify that the plc and sensor have proper power supply voltages. then the technician should verify that the plc is receiving a signal from the sensor
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the primary use of building and equipment grounding is to remove fault currents as fast as possible by using fuses or circuit breakers to disconnect power. the NEC states that building and equipment grounding systems using single made electrodes mus have a resistance of less than 25 omhs
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the resistance a persons body offers to the flow of current varies. swaty hands have less resistance than dry hands. a wet floor has less reistance than a dry floor. the lower the resistance the greater the current flow and greater the severity of shock.
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the standard unit of memory for a plc is the word. a word is 16 bits. a bit is the smallest unit of memory. bits are numbered right to left starting at 0. a nibble is a group of 4 bits. a byte is a group of 8 bits.
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the status lights of the plc output section or module indicate which output components are energized and which output componetns are de-energized.
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the technician should actuate the sensor to cause it to change state which will cause a change in current or voltage to the plc. when a change in current or voltage is measured, the sensor and wiring from the sensor to the plc can be eliminated as the source of the problem.
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All analog output devices must be connected through an interface device such as an analog SSR or relay.
false
All timer instructions consist of four words.
false
An undervoltage occurs when there is more than a 10% decrease in voltage for 0.5 cycles to one minute.
false
Emergency stop buttons must be wired directly to a PLC.
false
For individual conductors, the color blue is used to identify AC wiring and the color red is used for DC wiring.
false
On a multimeter, the abbreviation µA represents milliamperes.
false
RES instructions are used with TOF instructions.
false
The error code 03 in some PLCs indicates that a processor does not meet the required software level.
false
The output voltage from a transformer should not drop more than 15% from a no-load condition to a fully loaded condition.
false
Typically, enclosure cooling fans are replaced every five to seven years.
false
A(n) ? is a dual-voltage unit used to set the power rating of a PLC.
jumper link
bit files or "B" files are defaulted to file 3 and files 9-225 can also be configured as B files. File numbers are included in addresses. Addresses are formatted as word/bits, words, or bits
book
The status bar is the section that contains current status information and provides information on how to use the software.
true
When a technician is finished with the Force function, all forces must be removed.
true
PLC input sections or modules are designed for any type of analog input signal.
false
When loads are connected to a PLC that exceed the current rating of the PLC output power supply, the voltage output of the PLC will increase.
false
When using PLC programming software, pressing the F8 key generates a window that displays Help information.
false
? is/are an eye and face protection device that covers the entire face with a plastic shield and is used for protection from flying objects.
A face shield
Class C protective helmets are manufactured with lighter materials yet provide adequate impact protection. a Class E helmet is best when working on plc systems because plcs may be controlling high voltage electrical systems and equipment
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Data table files 0-8 are preconfigured and the file type cannot be changed. data table files 9-225 are configured by the technician
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Ensure that the plc and all associated hardware is securely mounted in the proper location. loose screws and bolts cause vibration, which can cause plug in circuit boards to loosen, open circuits, and arc.
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current sourcing pnp transistor switching. when using a pnp transistor type input device the load is connected between the negative terminal of the supply voltage and the output terminal of the switch or sensor. when the switch detects a target electron flows through the transistor and the plc input terminal is energized.
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electrically erasable programmable read only memory (EEPROM) is a type of nonvolatile memory that is retained when power is lost. EEPROM is used in plcs to provide a bakup for the ram memory.
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input devices and output components can be programmed in nested branches. nested branches are branches that have varying start and or end points.
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motor drives and ssrs are used with analog signals because a drive uses the varying analog signal to control the speed of a motor while an ssr uses an analog signal to control currents well over 100 A
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xic (examin if closed) are input instructions. XIC instructions are true when the address of the insturction contains a "1".
book
A byte is a group of four bits.
false
A variable frequency drive cannot accept an analog signal from a 1-kiloohm to 10-kiloohm variable resistor (potentiometer), a 0-volt DC to 10-volt DC voltage source, or a 4-milliampere to 20-milliampere current source as a control signal.
false
On a test instrument, two straight lines (one solid and one dashed) are used to represent AC current or voltage.
false
Unlike the Find All function, the Cross Reference function only displays the instructions with the same address.
false
Using the Force command during startup does not verify that the wiring to input devices and output components is in working order.
false
When a grounding connection must be made to the interior of a metal enclosure, any paint coatings must remain intact.
false
When an input terminal is forced, the LED for the forced input terminal lights up.
false
Energized maintenance is maintenance that verifies that the master control relay (MCR) is functioning correctly, voltages are within specified range, and no abnormal conditions exist.
true
In most circuits in which the load is rated at 115 volts AC, the control circuit is operated at a lower voltage level than the loads.
true
Magnetic motor starters, heating contactors, lighting contactors, and mechanical relays are not used with analog signals from a PLC.
true
Program backup is the final step in PLC maintenance.
true
The debugging process typically starts at the beginning of a program.
true
The ladder view is the section of the programming window that contains the programming diagram.
true
The number and type of I/Os cannot be changed in a fixed PLC.
true
To determine if there is a leakage current problem, measure the OFF-state leakage current and compare that value to the specified minimum operating current of the PLC input section or module.
true
? grounding is the connection of machinery electrical systems to earth ground to reduce the chance of electrical shock by grounding all non-current-carrying exposed metal.
Equipment
1. close and secure the plc enclosure door. remove the LOTO 2. turn the disconnect on. stand to the side of a plc enclosure when energizing in case of a major electrical fault or failure.
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1. locate the control transformer to be tested. the control transformer is fed power on the primary side from the main fuse or circuit breaker discconnect. 2. connect the test leads to the test instrument and set the multimeter to measure AC voltage at the highest possible voltage in the circuit
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A TOF instruction starts timing when the logic preceding he instruction on the rung changes from true to false. when a TOF instruction starts timing, the accumulated value begins to count time base intervals until the accumulated value equals the preset value.
book
A timer preset value is the number of time base intervals a timer instruction is programmed to accomplish. the preset is multiplied by the time base to determine a timing duration. for ex a timer with a preset value of 200 and a time vase of .01 works with a time duration of 2 sec (200 x .01= 2)
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All plcs have output components such as lamps solenoids and motor starters connected to output terminals. the output terminals of a plc are powered by a specific voltage or voltage range the type of voltage (AC or DC) and voltage level (12V, 24V, and 115V) used for a plc are based on the loads controlled by the plc.
book
Which safety label description indicates an imminently hazardous situation, that, if not avoided, will result in death or serious injury?
Danger
