PROGRAMMABLE LOGIC CONTROLLERS 5TH EDIT ION PETRUZELLA SOLUTIONS MANUAL Answers to Chapter 2 Review Questions 1. To accept signals from the machine or process de vices and to convert them into s ignals that can be used by the controller 2. To convert controller signals into external signals that are used to control the machine or process 3. a) A rack that is located away from the processor module near the field devices b) To mini mize the amount of wiring required 4. By its address 5. Type refers to an input or output Slot refers to the physical location of the I/O module Word and bit refers to the actual module terminal connection 6. Bit level addressing specifies a discrete device that is conn ected to a specific terminal. Word level addressing specifies an analog device connected to a module that uses a word of information. 7. In tag-based addressing you use a tag (alphanume ric name) to address data (variables). In rack/slot-based addressing a fixed num eric format is used to identify the address data. 8. An input/output PC interfac e card 9. Combination I/O modul es 10. Connections for the power supp ly 11. For ease of wiring and replacing modul es 12. The advantage with the high-density modu le is that it is poss ible to inst all up to 64 inputs or outputs in one slot for greater space savings. The disadv antage is that the high-density output modul es cannot handle as mu ch current per output. 13. ON/O FF devices such as selector switches, pu shbuttons and limit swi tches 14. ON/O FF devices such as lights, solenoids and motor starters 15. The backplane supp lies current and volt age for the modu les from the power supp ly 16. An opti cal isolator is used to p rovide electrical isolation b etween the field wi ring and the PLC backplane internal circuitry. 17. Power and Logic sections 18. Senses when a signal is received Converts the input s ignal to the correct voltage level Isolates the PLC from the input volt age or current Sends a signal to the processor indi cating which sensor o riginated the signal 19. T riac 20. a) 1 amp p er point b) A control relay is con nected to the output modul e. The contacts of t he control relay are then used to control the larger load. 21. T ransistor 22. A dis crete relay-type module uses an electromechanical relay element for switching which allow it to wo rk for AC or DC applications. 23. a) Sinking and sou rcing are terms used to describe a current signal flow relationsh ip between field input and output d evices in a control system and th eir power supply. b) Sourcing 24. Dis crete I/O modul es allow only ON/OFF devices to be connected. Analog I/O modul es allow analog or varying volt age or current devices to be connected. 25. Used to convert analog signals to an equivalent digital value 26. Used to convert digital signals to an equivalent analog value 27. Voltage sensing and current sensing 28. T emperature, speed, level, flow, weight, pressure, and pos ition 29. A twis ted shi elded pair cable is used in wi ring the circuit to reduce unwanted electrical noise signals that can be induced in the condu ctors from other wiring 30. Unipol ar modul es can accept an input s ignal that varies in the positive direction on ly. Bipolar signals swing between a maximum n egative value and a maximum pos itive value. 31. The analog input channel is capable of sensing voltages down to 0.3V in crements. 32. The loop pow er may be suppli ed by the sensor or may be provided by the analog output module 33. Control valves, chart recorder, electronic drives 34. a) Used to count pulses su ch as motor encoders that occur at very high speeds b) Allows the use of thumbwh eel swi tches for feeding information to a PLC c) Allows the transmitting and receiving of TTL signals for communi cation with the PLC’s processor d) Used to monitor the output of in cremental or absolute encoders e) Allows the transmitting and receiving of ASCII files f) Provides pulse tr ains to a stepper-motor t ranslator, which enables control of a stepper motor g) Enables a PLC to operate devices that require BCD-coded signals 35. a) Used to m aintain a process variable such as temperature, flow, level, or sp eed within set limits of a specified set point. b) Used in applications involving accurate high-speed machining and packaging operations c) Used to establish point -to-pint connections with oth er intelligent devices for the exchange of data 36. a) Specifies the magnitude and type of voltage signal that will be accepted by the input b) Specifies a minimum ON -state voltage that is the minimum vo ltage at whi ch logic 1 is recognized as absolut ely ON; and a maximum O FF-state voltage which is the voltage at which logic 0 is recognized as absolutely OFF c) Specifies the minimum input current that the input devices must be capable of driving to operate the input circuit d) Specifies what the maximum t emperature of the air surroundi ng the I/O modules should be for best operating conditions e) Specifies the maximum time duration required by an input module's circuitry to recognize that a field device has swit ched ON (input ON -delay) or switched OFF (input OFF-delay) f) Specifies the magnitude and type of user supp ly voltage at whi ch a discrete output module is desi gned to o perate g) Specifies the maximum current that a single output and the module as a whole can safely carry under load (at rated voltage) h) Specifies the maximum inrush current and du ration for which an output circuit can exceed its maximum continuous cu rrent rating i) This spe cification wi ll designate whether the particular modu le's des ign has individu al protection for each circuit or if fuse p rotection is prov ided for groups (e.g. 4 or 8) of outputs j) Specifies the amount of current still condu cting through an output circuit even after the output h as been turned off k) Rates the modu le's capacity for sust aining an excessive voltage at its input or output terminal l) This spe cification d efines the number of field inputs or outputs that can be connected to a single module m) This v alue indicates the amount of current the module requires from the backplane 37. a) Specifies the number of analog channels that can be connected to the module b) The voltage or current signal ranges that an analog input module is desi gned to a ccept c) This spe cification d efines the current or voltage signal ranges that a particular analog
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