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EENG421 Ch. 4, 5, 6
Timers, Counters, Arithmetic
| Question | Answer |
|---|---|
| What are the two delay types? | Fixed or variable |
| How do delays work? | They suspend movement of the contacts when the coil is energized, de-energized, or both |
| What is pneumatics? | Pneumatics is the controlled release of air that develops a time-delay in a relay |
| What is the range of on/off delay of a pneumatic timing relay? | 0.05s - 180s with an accuracy of +/- 10 percent. |
| What is the difference between timed contacts and instantaneous contacts? | Timed contacts react to a time delay (either on/off delay), instantaneous contacts operate independently from the timing process (basically standard control relay contacts) |
| What are the biggest differences between electronic timing relays and pneumatic timing relays? | Electronic timing relays are more accurate, repeatable, and economical than pneumatic timing relays |
| What is the supply voltage range of electronic timing relays? | 24 to 48 VDC 24 to 240 VAC |
| What is the time range of an electronic timing relay? | 0.05 seconds to 60 hours +/- 5% accuracy, +/- 0.2 percent repeatability |
| Are electronic timing relays part of a PLC? | No, they are stand alone devices |
| What kind of instruction is a PLC timer? | An output instruction |
| What are some advantages of using timers in PLCs? Disadvantages? | Advantages: settings and the number of timers are easily changed, highly accurate and repeatable Disadvantages: the accuracy of the timed event could be affected by long scan times |
| How many words are used in a timer's memory? What are they mapped to? | 3 words Word 0 - EN, TT, DN bits Word 1 - Preset Value Word 2 - Accumulated value |
| What do the letters stand for in this addressing format: Tf:e.s/b | T: Timer f: file number (4 for timers) e: timer number (0 to 255) s: word number (0 to 2) b: bit number (0 to 15) |
| What is this address referencing? T4:0/15 | Enable bit of timer 0 |
| What is this address referencing? T4:2/14 | Timer timing bit of timer 2 |
| What is this address referencing? T4:15/13 | Done bit of timer 15 |
| What is this address referencing? T4:5.1 | Preset value of timer 5 |
| What is this address referencing? T4:10.2 | Accumulator value of timer 10 |
| What is this address referencing? T4:20.1/0 | Bit 0 of the preset value of timer number 20 |
| What is this address referencing? T4:3.2/11 | Bit 11 of the accumulator value of timer 3 |
| What is this address referencing? T9:0.ACC | The accumulator word for timer 0 in timer file 9 |
| What is this address referencing? T255:255/EN | The enable bit for the last available timer in the system |
| What is the relation between TON and timer relay contact configurations? | A TON is an on-delay timing relay. A TON done bit is like a normally open, timed closed timing relay contact |
| What is the relation between TOF and timer relay contact configurations? | A TOF is an off-delay timing relay. A TOF timer done bit is the same as the normally open, timed open relay contact |
| When is the TON enable bit true? | When the timer rung is true |
| When is the TON timer timing bit true? | When the timer rung is true AND acc < pre |
| When is the TON done bit true? | When the timer rung is true AND acc >= pre |
| When is the TON enable bit false? | When the timer rung is false |
| When is the TON timer timing bit false? | When the timer rung is false OR acc >= pre OR the done bit is true |
| When is the TON done bit false? | When the timer rung is false OR acc < pre |
| When is the TOF enable bit true? | When the timer rung is true |
| When is the TOF timer timing bit true? | When the timer rung is false AND acc < pre |
| When is the TOF done bit true? | When the timer rung is true OR the TT bit is true |
| When is the TOF enable bit false? | When the timer rung is false |
| When is the TOF timer timing bit false? | When the timer rung is true OR acc >= pre OR the done bit is false |
| When is the TOF done bit false? | When the timer rung is false AND acc >= pre |
| Is the RTO on or off delay? | On delay |
| When is the RTO enable bit true? | When the timer rung is true |
| When is the RTO timer timing bit true? | When the timer rung is true AND acc < pre |
| When is the RTO done bit true? | When acc >= pre |
| When is the RTO enable bit false? | When the timer rung is false |
| When is the RTO timer timing bit false? | When the timer rung is false OR acc >= pre |
| When is the RTO done bit false? | When the reset instruction is initiated OR timer rung is true AND acc < pre |
| When can reset occur for an RTO timer? | At any time during the RTO process. It is independent of input conditions and RTO bits (en, tt, done) |
| What is the main differences for logix timers? | Timer outputs are placed in series on a single rung, tag names are used instead of file number addresses |
| Is there a limit to the number of timers that can be placed in a cascade configuration? | No |
| When are cascaded timers generally used? | When the time delay exceeds the maximum delay capability of a single timer. |
| What does cascading timers mean? | One timer's output triggers another timer's input |
| What are the two types of counter instruction? | Count up and count down |
| What type of instruction is a counter? | An output instruction that control an output device after the counter accumulator reaches a certain value |
| How many counters does SLC 500 have in file C5? | 256, an additional 256 each for files C9 to C255 |
| How many counters does PLC5 have in file C5? | 1000 |
| What is the range of the preset value for PLC5 and SLC500? | -32,768 to +32,767 |
| How are negative values stored for PLC5 and SLC500 counters? | Using 2's complement |
| What is the range of the acc value for PLC5 and SLC500? | -32,768 to +32,767 |
| What does the acc value default to when the counter is reset? | zero |
| What is the preset value address for a counter? | C5:0.PRE |
| What is the accumulator value address for a counter? | C5:0.ACC |
| When is the Count Up (CU) enable bit true? | When the up counter rung is true |
| When is the Count Up (CU) enable bit false? | When the counter rung is false |
| When is the Count Down (CD) enable bit true? | When the down counter rung is true |
| When is the Count Down (CD) enable bit false? | When the down counter rung is false |
| What are the five output bits of a counter? | Count up (CU) enable, count down (CD) enable, count up overflow (OV), count down underflow (UN), and done (DN) |
| When is the done bit true for a counter? | When acc >= pre |
| When is the done bit false for a counter? | When acc < pre |
| T/F: The counter acc bit continues to increment after the DN bit is true. | True. A reset instruction is required to return acc to zero |
| When is the Count Up Overflow (OV) bit true? What happens? | When the counter increments above +32,767. On the next count the acc wraps to -32,768 |
| When is the Count Down Underflow (UN) bit true? What happens? | When the counter increments below -32,768. On the next count the acc wraps to +32,767 |
| How many words are used to store control bit values and operational parameters? | 3 words |
| What is the maximum pulse of a HSC in SLC500 and MicroLogix? | 8kHz |
| What is a high speed controller (HSC)? | A HSC is like a CTU counter that counts false to true transitions at input terminal I:0/0, If HSC rung is true, pulses at I:0/0 are counted. |
| T/F: rung transitions and scan times to not effect the count of an HSC | True. Because the HSC operates asynchronously/independent of the ladder program scan |
| Are the HSC output bits retentive or non-retentive? | non-retentive |
| T/F: More than one HSC is allowed for SLC500 and Micrologix | False. Only one is allowed and activation jumper must be clipped |
| What is the extra bit of a HSC? | The update accumulator (UA). |
| Where is the update accumulator bit located? | Bit 10 of C5:0.0 of the counter's data register |
| What happens when the UA bit is true? | The acc register is updated to the count value in the HSC hardware counter |
| What does the reset instruction do for a counter? | Resets the accumulator value back to zero |
| What does the ADD instruction do? | Adds source A to source B and stores the result in the destination |
| What does the SUB instruction do? | Subtracts source B from source A and stores the result in the destination |
| What does the MUL instruction do? | Multiplies source A by source B and stores the result in the destination |
| What does the DIV instruction do? | Divides source A by source B and stores the result in the destination and math register |
| What does the DDV instruction do? | Divides the contents of the math register by the source and stores the result in the destination and the math register |
| What does the CLR instruction do? | Sets all bits of a word to zero |
| What does the SQR instruction do? | Calculates the square root of the absolute value of the source and places the integer result in the destination |
| What does the SCP instruction do? | Produces a scaled output value that has a linear relationship between the input and scaled values |
| What does the SCL instruction do? | Multiplies the source by a specified rate, adds to an offset value, and stores the result in the destination |
| What does the ABS instruction do? | Calculates the absolute value of the source and places the result in the destination |
| What does the CPT instruction do? | Evaluates an expression and stores the result in the destination |
| What does the SWP instruction do? | Swaps the low and high bytes of a specified number of words in a bit, integer, ASCII, or string file |
| What does the ASN instruction do? | Takes the arc sine of a number and stores the result in radians in the destination |
| What does the ACS instruction do? | Takes the arc cos of a number and stores the result in radians in the destination |
| What does the ATN instruction do? | Takes the arc tangent of a number and stores the results in radians in the destination |
| What does the COS instruction do? | Takes the cosine of a number and stores it in the destination |
| What does the LN instruction do? | Takes the natural log of the value in the source and stores it in the destination |
| What does the LOG instruction do? | Takes the log base 10 of the value in the source and stores the result in the destination |
| What does the SIN instruction do? | Takes the sine of a number and stores it in the destination |
| What does the TAN instruction do? | Takes the tangent of a number and stores it in the destination |
| What does the XPY instruction do? | Raises a value (X) to a power (Y) and stores the result in the destination |
| T/F: If the value of a source is negative, the SQR instruction will produce an error | False. It will take the square root of the absolute value of the source value |
| What does the MOV instruction do? | Moves/copies data from one location to another |
| What does MVM do? | MVM (Move with a mask) moves only designated bits from one place to another |
| What does the NEG instruction do? | The negate instruction moves the negative representation of the data from one location to another |
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