Lesson 14

Cyclogram and work cycle

The ordinary calculation takes every consumer at its full flow, all the time. That is right for sizing the pipes and wrong for the money: real consumers blow, wait and blow again. The cyclogram tells the program when each of them runs — and turns the peak into the air a round really costs.

What a cyclogram is

A time diagram of one round of work. Each consumer of a compressor gets a row with a step line: up — it runs, down — it is off. The round repeats for all the working hours of Input parameters. EasyCAS calculates the network at every moment where something switches, so for every piece of the round it knows the flow, the pressure the compressor must give and what that air costs.

1. Calculate the network as it is drawn

   Open lesson8.gf9 and save it at once as lesson14.gf9. The toolbar switch must read Design. Input parameters are saved in the scheme file, so first check them on the Input parameters tab against lesson 1 — the money of this lesson depends on them:

   Input parameter	Value	What it changes here
   Normal temperature (C)	20	the normal litre of every Qn
   Ambient temperature (C)	20	at 25 the pipes pass less air: Qn 1610.42 instead of 1637.89
   Pressure of air (Bar)	6	the pressure the price of air is quoted at
   Compressed air cost (€/Nm³)	0.024
   Hours per day	8	with Days per year 240 — 1920 hours a year
   Days per year	240
   Carbon intensity (gCO2/kWh)	400	only the CO2 rows

   Press Calculate and click COMP:

   Row, COMP	Expected	Unit
   Pout	6.1656	bar	6 bar at the pipes plus the losses
   Qn	1637.89	NL/min	B1 1048.25 + B2 589.64
   Cs	4603.41	€	a year, both pipes blowing all 1920 hours

   Other figures? With Hours per day 4, Ambient temperature 25 and Pressure of air 7 the same network gives Qn 1610.42 NL/min and Cs 2062.25 €: the price of air at 6.17 bar becomes 0.024 × (6.17 / 7)^0.603 = 0.02223 €/Nm³, and 96.6 Nm³/h × 960 h × 0.02223 = 2062 €. Nothing is wrong with the calculation — the inputs are not the lesson's. Set them as above and calculate again.

   Both open pipes blow non-stop in this calculation. On a real machine B1 cleans a part for half a minute and B2 dries it for a few seconds; between parts both are off.

2. Open the cyclogram

   The Source field on the toolbar names the compressor whose network you look at — here the only one, COMP. The IDs on this page are those of a network drawn in the order COMP, T1, P2, P3, P1, B1, B2: COMP is ID1, B1 ID12, B2 ID14. IDs follow the order the items were drawn, so yours may differ; the captions on the sheet tell which is which. Press the button next to it, Cyclogram. It is greyed only when the scheme has no compressed air source; with Source empty a click first lists the sources to choose from.

   The window Cyclogram for compressor ID1 has a row per consumer of this source, each headed by its card label and ID: Tube_blowing : ID12 (B1) and Tube_blowing : ID14 (B2). Both step lines are up for the whole width: a consumer without switching points runs all the time, as in the ordinary calculation.

   The round is 10 minutes long when nothing has been set. Press Time interval on the bottom panel (or Actions → Time interval), set Min to 1 and the other fields to 0, press Set. The time axis now runs from 0 to 1 minute, and the field under the button reads 0:00:01:00:000 — days, hours, minutes, seconds, milliseconds, as everywhere in this window.

   At the bottom right of the window the captions Pout and Qn show the pressure and the flow of the compressor at the visor. (Their ticks, with CbCG, draw the two curves in a band under the rows; the Compressor window of step 6 does that better.)

   Shown	Expected
   Qn	1637.8924 NL/min	both pipes all the round
   Pout	6.1656 bar	the Pout of the ordinary calculation
   Title: Cost of air per cycle	0.04 €	one minute of both pipes, 0.03996 € rounded

3. Draw the round of B1 with the mouse

   B1 blows for the first half of the round and stops. Right-click the row of B1 about the middle of the round. The click makes the row current, puts the visor there and opens a menu that offers only the switching that changes something — here Switch Off here. Choose it: the step line drops at the moment you clicked.

   Now make the moment exact. Point at the falling edge: the pointer becomes a double bar with arrows. Drag the edge — the visor follows it and the time under the plot shows where it is — and release it at 0:30. For an exact value without dragging, right-click the row and choose Set point at exact time...: the Switching point window takes the moment in fields Days : Hours : Min : Sec : ms — type 30 into Sec — and under Power the state from that moment on, On or Off; press Set. The length of the round is shown under the fields: the moment must be shorter.

   Every change is recalculated at once; the cost in the title drops. Undo and Redo on the bottom panel step through the changes of the current row.

4. Give B2 its round as text

   A cyclogram can be copied as plain text. Right-click the row of B1 and choose Copy cyclogram, then paste into Notepad. You see:

   EasyCAS cyclogram 1
   # Tube_blowing
   source=ID1
   cycle_ms=60000
   initial=on
   30000	off

   The first line tells a cyclogram from any other text; # starts a comment; initial is the state at the start of the round; every other line is a moment in milliseconds, a tab (or a space) and the state after it. B2 dries the part from the 20th to the 38th second, so change the text to:

   EasyCAS cyclogram 1
   cycle_ms=60000
   initial=off
   20000	on
   38000	off

   Copy it, right-click the row of B2 and choose Paste cyclogram. B2 is now up from 0:20 to 0:38. A text whose cycle_ms differs from the round of the scheme makes the program ask: Scale to this cycle stretches the times, Keep times drops the ones beyond the end.

5. Read the round

   The dashed lines across all rows mark every switching moment of the scheme. Between them nothing changes, and the network is calculated once per piece:

   Piece of the round	Running	Qn, NL/min	Pout, bar
   0:00 – 0:20	B1	1048.25	≈ 6.10
   0:20 – 0:30	B1 and B2	1637.89	6.1656
   0:30 – 0:38	B2	589.64	6.0348
   0:38 – 1:00	nothing	0	0

   Move the visor along the round (click on the time axis, or Set visor) and watch the captions of Pout and Qn follow the table. Where nothing runs there is nothing to deliver, and Pout reads 0. Each consumer gets its design flow at its 6 bar; what changes from piece to piece is how much pressure the compressor must give to push that flow through P1 — the less air, the less loss.

   The title now reads Cost of air per cycle: 0.017 € — the title rounds to four places after the point.

   Check by hand: the mean, the peak and the year

   Mean flow: (1048.25 × 30 + 589.64 × 18) / 60 = 701 NL/min — 43 % of the 1638 the ordinary calculation takes. The peak stays 1638 NL/min, for the ten seconds when both blow: the pipes must still be sized for it. The money: each piece costs 0.024 €/Nm³ × (Pout / 6)^0.603 × Qn × its length — 0.00847 + 0.00666 + 0.00189 = 0.01702 € a round. 8 h × 240 days is 115 200 one-minute rounds a year: 0.01702 × 115 200 ≈ 1961 € instead of the 4603 € of the ordinary calculation.

6. Look at the compressor on its own

   The captions give one moment; the whole round of the compressor is in a window of its own. Press Compressor on the bottom panel (or Actions → Compressor P/Q chart): the window Compressor pressure and flow gives the pressure and the flow a band and a scale each, and the line under the plot reads the visor in d:h:m:s:ms with both values. It shows the same data, not a second calculation, and shares the visor with the cyclogram — move it in one window and it moves in the other. Y axis from zero switches between a scale from zero, which shows how deep a change really is, and one fitted to the curve, which shows its shape.

7. Close the window and calculate again

   Close the cyclogram (Exit). The rows of the items are empty now: while the window was open, the program calculated the scheme at single moments of the round, and those numbers are not the design state. Closing the window clears them. Press Calculate again.

   The ordinary calculation has not changed — it still takes both pipes at once, because the pipes must carry the peak. What the cycle changes is everything that is about the average:

   • Compressor selection (lesson 9) now works the machine over the round: the bold warning that every consumer is taken at its maximum is gone, and so is the row Consumers always at maximum on the card. The head of the window still gives the demand of the network at its peak — the machine must be able to deliver it;
   • in Audit mode the running share of each consumer comes from the cycle instead of Audit utilization;
   • the air consumption data sheet takes its mean and peak from it.

   Save lesson14.gf9: the cyclogram, the round length and the size of the window are kept in the file.

8. Hand the cycle to the plant as a file

   The times of a real machine come from the people who set it up. Rather than read them out over the phone, send them a form. In the cyclogram choose Actions → Export consumers list; the file is offered as events_ID1.xlsx (choose the CSV filter for a text file). For a network without pulse valves it is the form CONSUMER SWITCHING TIMES:

   # EasyCAS Work Cycle - CONSUMER SWITCHING TIMES
   # Compressor (source): ID1
   # One row per consumer: switched on at fires_at_ms for duration_ms.
   # More switch-ons per cycle - more column pairs to the right.
   # Empty pairs - no cyclogram yet. A row with all pairs empty clears it;
   #   a consumer whose row is deleted keeps its current cyclogram.
   # element is the instance ID from the schematic - do NOT rename it.
   [parameters]
   key;value;unit
   consumers;2
   cycle_time;60000;ms
   [sequence]
   seq;element;fires_at_ms;duration_ms
   1;ID12;0;30000
   2;ID14;20000;18000

   One line per consumer: when it switches on and for how long. A consumer without a cyclogram comes out with the time columns empty — the file is both a snapshot of what is drawn and a form for what is left. More switch-ons in a round go to the right as further fires_at_ms;duration_ms pairs. Do not rename the element column: the import finds each item by its ID.

   Actions → Import events reads a filled file back, draws it and recalculates. If any line is refused, nothing is written to the scheme, and the report lists the lines to fix. A consumer whose line was deleted from the file keeps its cyclogram.

When it does not work

Try this next

• Drag the rising edge of B2 with Shift held: the whole pulse moves and keeps its length. Put it at 0:30 – 0:48, so that B2 starts as B1 stops. The peak drops to 1048 NL/min, the cost of a round hardly changes: the air is the same, only the moment. A smaller peak means a smaller compressor and thinner pipes — lesson 9.
• Add a second shot of B2 in the exported CSV — 2;ID14;20000;18000;50000;5000 — and import it. B2 now fires twice a round.
• Copy the cyclogram of B1 and paste it into a cyclogram of another scheme with a 10-minute round: choose Scale to this cycle and see the times stretched tenfold.

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