Industrielle styresystemer - Wiki
The Code is implemented in accordens to the requirments given in the function description. Quickly summerized it describes the following,
- Survey and report the moisture in the air,
- Sound an alarm after 10 mintues if the moisture deviates more than +-5%rH away from the setpoint.
- In case of an alarm, turn on fans to ensure a well ventilated facility
The Code for the Moisture sensor is based on its technical data (Bosch, 2024), where 0v = 0%rH which linearly scales to 5v = 100%rH. This means that linear interpolation is utilized to scale the input voltage too an output in %rH.
Linear interpolation is performed with the following function (Chapra and Canale, 2015),
This means that the inputs needs to be,
- sensor_reading:REAL;
- set_point_in_pRhREAL;
- alarm_delay:TIME;
- max_pRh:REAL;
- max_pRh_in_volts:REAL;
- min_pRh:REAL;
- min_pRh_in_volts:REAL;
And the outputs needs to be,
- pRh_read:REAL;
- alarm_high:BOOL;
- alarm_low:BOOL;
With the following internal variables,
- alarm_since_trig:TIME;
- alarm_high_trig:BOOL;
- alarm_low_trig:BOOL;
- alarm_high_trig_0:BOOL;
- alarm_low_trig_0:BOOL;
The coded implementation looks like this,
Visually the new function block looks as following,
References:
Chapra, S.C. and Canale, R.P. (2015). Numerical Methods for Engineers. 7th ed. New York: McGraw-Hill Education. [pdf] Available at: https://gdcboysang.ac.in/About/Droid/uploads/Numerical%20Methods.pdf (Accessed: 28 May 2024).
Bosch. (2024). BME688: Digital low power gas, pressure, temperature & humidity sensor with AI. [pdf] February 2024, Document revision 1.3. Available at: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme688-ds000.pdf (Accessed: 28 May 2024).
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