GY-63_MS5611/libraries/pressure

pressure

Arduino library for pressure conversion.

Description

Simple library to convert between several pressure formats. It consists of a number of setters and getters and internally it uses millibar. In fact it just hides all conversion constants.

Pressure is implemented as a float so this limits the precision of the value.

If other constants / conversions are needed please open an issue on GitHub.

Note: as a conversion uses two steps the conversion error might be (bit) larger than in a single conversion step as there are two multiplications involved.

Note: constants need to be verified.

Interface

Constructor

• pressure(float value = 0.0) Constructor, with optional initial value.

Setters

• void setMilliBar(float value) sets pressure in milliBar.
• void setBar(float value) sets pressure in bar.
• void setPSI(float value) sets pressure in PSI = Pounds per Square Inch.
• void setATM(float value) sets pressure in Atmosphere.
• void setDynes(float value) sets pressure in Dynes.
• void setInchHg(float value) sets pressure in inches mercury.
• void setInchH2O(float value) sets pressure in inches water.
• void setPascal(float value) sets pressure in Pascal. Note this is the SI unit.
• void setTORR(float value) sets pressure in TORR.
• void setCmHg(float value) sets pressure in centimetre mercury.
• void setCmH2O(float value) sets pressure in centimetre water.
• void setMSW(float value) sets pressure in Meters of Sea Water. (under water pressure unit).

Getters

• float getMilliBar() returns pressure in milliBar.
• float getBar() returns pressure in bar.
• float getPSI() returns pressure in PSI = Pounds per Square Inch.
• float getATM() returns pressure in Atmosphere.
• float getDynes() returns pressure in Dynes.
• float getInchHg() returns pressure in inches mercury.
• float getInchH2O() returns pressure in inches water.
• float getPascal() returns pressure in Pascal. Note this is the SI unit.
• float getTORR() returns pressure in TORR.
• float getCmHg() returns pressure in centimetre mercury.
• float getCmH2O() returns pressure in centimetre water.
• float getMSW() returns pressure in Meters of Sea Water. (under water pressure unit).

Gas law (experimental see below)

The change() function is applied to the current internal pressure.

• void change(float T1, float T2, float V1, float V2, float N1, float N2)
  • apply changing temperature (Kelvin),
  • volume (m3) and moles.
  • If an parameter does not change fill in 1 for both before (T1,V1, N1) and after (T2,V2,n2).
• void changeT(float T1, float T2) only change temperature. T in Kelvin.
• void changeV(float V1, float V2) only change volume.
• void changeN(float N1, float N2) only change moles.

Constants

The library has a number of constants to convert units. See the pressure.h file. These constants can be used to write specific convertors or define specific constants.

A dedicated conversion is faster as it has only one float multiplication runtime.

inline float PSI2MSW(float value)
{
  return value * (PSI2MILLIBAR * MILLIBAR2MSW);
}

or

#define PSI2MSW     (PSI2MILLIBAR * MILLIBAR2MSW)
...
float out = in * (PSI2MSW);

Operation

pressure P;

...

P.setDynes(1000);
Serial.print("mBar: ");
Serial.println(P.getMilliBar()); // 1000 Dynes in mBar
Serial.print("TORR: ");
Serial.println(P.getTORR());     // 1000 Dynes in Torr

Obsolete

Version 0.1.0 has incorrect setters. fixed in version 0.2.0.

Experimental 0.2.1

Apply the ideal gas law : P x V / n x T = Constant

• void change(float T1, float T2, float V1, float V2, float N1, float N2)
  • T (temperature) in Kelvin,
  • V (volume) in identical units,
  • N (# atoms) in mole
• void changeT(float T1, float T2) only change temperature. T in Kelvin.
• void changeV(float V1, float V2) only change volume.
• void changeN(float N1, float N2) only change moles.

in code

pressure P;    
P.setPressure(...);
P.change(T1, T2, V1, V2, N1, N2);  // apply all changes.  
x = P.getPressure()

• do we need a changeTC(float T1, float T2) only change temperature, T in Celsius
• should functions return bool true on success ?

Kelvin = Celsius + 273.15;
Kelvin = (Fahrenheit - 32) \* 5 / 9 + 273.15;
Kelvin = Fahrenheit \* 5 / 9 + 290.93;  // one operator less.

Future

must

• update documentation
• find a good reference for conversion formula constants.

should

• test with gas law.
• calculate getter constants from setter constants. 1.0 / XXX
• rename parameters so they make more sense?

  void  setMilliBar(float milliBar )  { _pressure = milliBar; };
  void  setBar(float Bar)             { _pressure = Bar * BAR2MILLIBAR; };
  void  setPSI(float PSI)             { _pressure = PSI * PSI2MILLIBAR; };

could

• defaults for functions? 0 like constructor?
• move code to .cpp file ?
• change could return int indicating
  • 1: a change is made.
  • 0: no change is made
  • -1: parameter negative
• change could return a float indicating the new pressure in mBar?