Project: tolerance guard

For the base's breathing air you mix oxygen and nitrogen in a tank. The share should be 21 %. No pump hits it exactly, a band of a few percent is fine. That is exactly what you learned sap for this week.

The setup#

The analyzer delivers the oxygen share as RatioOxygen, a number from 0 to 1.

Milestones#

1. Within the band: if the share lies within TOL (relative) around TARGET, both pumps are off, “Mischung ok” lights up, the alarm is off.
2. Too little oxygen: the oxygen pump runs, the nitrogen pump does not, the alarm lights up.
3. Too much oxygen: the nitrogen pump runs, the oxygen pump does not, the alarm lights up.
4. Tolerance and display: with TOL 0.05, 22 % still counts as good, 22.5 % no longer. The display shows the deviation in percent of the target: (share − target) / target × 100.
5. Failure: if the analyzer is missing, no pump runs, the alarm lights up, the display shows −999.

Setting the relative tolerance#

sap allows a distance of TOL times the larger of the two values. At 22 % oxygen and TOL 0.05 that is 0.05 × 0.22 = 0.011. The distance to 0.21 is 0.01, so still within the band.

sap ok o2 TARGET TOL        # 1 within the band, 0 outside and on NaN
seqz tmp ok                 # 1 = action needed or failure
slt less o2 TARGET
and less less tmp

If you want a narrower band, you only make TOL smaller. For breathing air a few percent around 21 % are fine. For a fuel mixer you would regulate more tightly.