From 3905a56d4fce040f05b3e37a8771581f45d6c828 Mon Sep 17 00:00:00 2001 From: Steven Baltakatei Sandoval Date: Sat, 2 Oct 2021 04:22:16 +0000 Subject: [PATCH] feat(examples/a): Add absolute dew point temperature display mode --- examples/all-in-one-enviro-mini-bk.py | 149 +++++++++++++++++++++++++- 1 file changed, 145 insertions(+), 4 deletions(-) diff --git a/examples/all-in-one-enviro-mini-bk.py b/examples/all-in-one-enviro-mini-bk.py index 88c3475..de97514 100755 --- a/examples/all-in-one-enviro-mini-bk.py +++ b/examples/all-in-one-enviro-mini-bk.py @@ -211,6 +211,118 @@ def rel_to_abs(T,P,RH): return float(r); +def rel_to_dpt(T,P,RH): + """Returns dew point temperature given relative humidity. + + Inputs: + -------- + T : float + Absolute temperature in units Kelvin (K). + P : float + Total pressure in units Pascals (Pa). + RH : float + Relative humidity in units percent (%). + + Output: + -------- + T_d : float + Dew point temperature in units Kelvin (K). + + References: + -------- + 1. Sonntag, D. "Advancements in the field of hygrometry". 1994. https://doi.org/10.1127/metz/3/1994/51 + 2. Green, D. "Perry's Chemical Engineers' Handbook" (8th Edition). Page "12-4". McGraw-Hill Professional Publishing. 2007. + + Version: 0.0.1 + Author: Steven Baltakatei Sandoval + License: GPLv3+ + """ + + import math; + + # Check input types + T = float(T); + P = float(P); + RH = float(RH); + + #debug + # print('DEBUG:Input Temperature (K) :' + str(T)); + # print('DEBUG:Input Pressure (Pa) :' + str(P)); + # print('DEBUG:Input Rel. Humidity (%) :' + str(RH)); + + # Set constants and initial conversions + epsilon = 0.62198 # (molar mass of water vapor) / (molar mass of dry air) + t = T - 273.15; # Celsius from Kelvin + P_hpa = P / 100; # hectoPascals (hPa) from Pascals (Pa) + + # Calculate e_w(T), saturation vapor pressure of water in a pure phase, in Pascals + ln_e_w = -6096*T**-1 + 21.2409642 - 2.711193*10**-2*T + 1.673952*10**-5*T**2 + 2.433502*math.log(T); # Sonntag-1994 eq 7; e_w in Pascals + e_w = math.exp(ln_e_w); + e_w_hpa = e_w / 100; # also save e_w in hectoPascals (hPa) + # print('DEBUG:ln_e_w:' + str(ln_e_w)); # debug + # print('DEBUG:e_w:' + str(e_w)); # debug + + # Calculate f_w(P,T), enhancement factor for water + f_w = 1 + (10**-4*e_w_hpa)/(273 + t)*(((38 + 173*math.exp(-t/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22. + # print('DEBUG:f_w:' + str(f_w)); # debug + + # Calculate e_prime_w(P,T), saturation vapor pressure of water in air-water mixture, in Pascals + e_prime_w = f_w * e_w; # Sonntag-1994 eq 18 + # print('DEBUG:e_prime_w:' + str(e_prime_w)); # debug + + # Calculate e_prime, vapor pressure of water in air, in Pascals + e_prime = (RH / 100) * e_prime_w; + # print('DEBUG:e_prime:' + str(e_prime)); # debug + + n = 0; repeat_flag = True; + while repeat_flag == True: + # print('DEBUG:n:' + str(n)); # debug + + # Calculate f_w_td, the enhancement factor for water at dew point temperature. + if n == 0: + f = 1.0016 + 3.15*10**-6*P_hpa - (0.074 / P_hpa); # Sonntag-1994 eq 24 + f_w_td = f; # initial approximation + elif n > 0: + t_d_prev = float(t_d); # save previous t_d value for later comparison + f_w_td = 1 + (10**-4*e_w_hpa)/(273 + t_d)*(((38 + 173*math.exp(-t_d/43))*(1 - (e_w_hpa / P_hpa))) + ((6.39 + 4.28*math.exp(-t_d / 107))*((P_hpa / e_w_hpa) - 1))); # Sonntag-1994 eq 22. + # print('DEBUG:f_w_td:' + str(f_w_td)); # debug + + # Calculate e, the vapor pressure of water in the pure phase, in Pascals + e = (e_prime / f_w_td); # Sonntag-1994 eq 9 and 20 + # print('DEBUG:e:' + str(e)); # debug + + # Calculate y, an intermediate dew point calculation variable + y = math.log(e / 611.213); + # print('DEBUG:y:' + str(y)); # debug + + # Calculate t_d, the dew point temperature in degrees Celsius + t_d = 13.715*y + 8.4262*10**-1*y**2 + 1.9048*10**-2*y**3 + 7.8158*10**-3*y**4;# Sonntag-1994 eq 10 + # print('DEBUG:t_d:' + str(t_d)); # debug + + if n == 0: + # First run + repeat_flag = True; + else: + # Test t_d accuracy + t_d_diff = math.fabs(t_d - t_d_prev); + # print('DEBUG:t_d :' + str(t_d)); # debug + # print('DEBUG:t_d_prev:' + str(t_d_prev)); # debug + # print('DEBUG:t_d_diff:' + str(t_d_diff)); # debug + if t_d_diff < 0.01: + repeat_flag = False; + else: + repeat_flag = True; + + # Calculate T_d, the dew point temperature in Kelvin + T_d = 273.15 + t_d; + # print('DEBUG:T_d:' + str(T_d)); # debug + + if n > 100: + return T_d; # good enough + + # update loop counter + n += 1; + return T_d; # Tuning factor for compensation. Decrease this number to adjust the # temperature down, and increase to adjust up @@ -228,6 +340,7 @@ variables = ["temperature", "pressure", "humidity", "humidity_abs", + "dewpoint_temperature", "light"] values = {} # Initialize values dictionary for v in variables: @@ -258,13 +371,14 @@ def pollSensors(): # now_humidity_tuple (%) # now_humidity_abs_gkg_tuple (g water vapor / kg dry air) # now_illuminance_tuple (lux) - # Depends: time, bme280, ltr559, get_cpu_temperature(), rel_to_abs() + # Depends: time, bme280, ltr559, get_cpu_temperature(), rel_to_abs(), rel_to_dpt() # Tell function to modify these global variables global now_temp_tuple global now_pressure_tuple global now_humidity_tuple global now_humidity_abs_gkg_tuple + global now_humidity_dpt_c_tuple global now_illuminance_tuple # Initialize cpu_temps = [] @@ -290,6 +404,10 @@ def pollSensors(): now_humidity_abs = rel_to_abs(raw_temp_k, now_pressure_pa, now_humidity); # calc kg/kg abs humidity now_humidity_abs_gkg = now_humidity_abs * 1000; now_humidity_abs_gkg_tuple = (time.time_ns(), 'g/kg', now_humidity_abs_gkg); + # Calculate dew point temperature + now_humidity_dpt = rel_to_dpt(raw_temp_k, now_pressure_pa, now_humidity); # calc K dpt + now_humidity_dpt_c = now_humidity_dpt - 273.15; + now_humidity_dpt_c_tuple = (time.time_ns(), '°C', now_humidity_dpt_c); # Get light reading proximity = ltr559.get_proximity() # get proximity reading if proximity < 10: @@ -388,6 +506,7 @@ def updateBuffer(): global now_pressure_tuple global now_humidity_tuple global now_humidity_abs_gkg_tuple + global now_humidity_dpt_c_tuple global now_illuminance_tuple global varLenBuffer global fixLenBuffer @@ -402,6 +521,7 @@ def updateBuffer(): #print('DEBUG:now_pressure_tuple:' + str(now_pressure_tuple)) #print('DEBUG:now_humidity_tuple:' + str(now_humidity_tuple)) #print('DEBUG:now_humidity_abs_gkg_tuple:' + str(now_humidity_abs_gkg_tuple)) + #print('DEBUG:now_humidity_dpt_c_tuple:' + str(now_humidity_dpt_c_tuple)) #print('DEBUG:now_illuminance_tuple:' + str(now_illuminance_tuple)) # Append new sensor tuples to varying-length buffer @@ -413,8 +533,10 @@ def updateBuffer(): varLenBuffer[variables[2]].append(now_humidity_tuple) ## Absolute Humidity varLenBuffer[variables[3]].append(now_humidity_abs_gkg_tuple) + ## Dew Point Temperature + varLenBuffer[variables[4]].append(now_humidity_dpt_c_tuple) ## Illuminance - varLenBuffer[variables[4]].append(now_illuminance_tuple) + varLenBuffer[variables[5]].append(now_illuminance_tuple) #print('DEBUG:varLenBuffer:' + str(varLenBuffer)) # Trim outdated sensor tuples from varying-length buffer @@ -544,10 +666,29 @@ try: # print('DEBUG:now_pressure:' + str(now_pressure)); # print('DEBUG:now_pressure_pa:' + str(now_pressure_pa)); # print('DEBUG:now_humidity:' + str(now_humidity)); - # print('DEBUG:now_humidity_abs_gkg:' + str(data)); + # print('DEBUG:now_humidity_abs_gkg:' + str(now_humidity_abs_gkg)); display_text2(variables[mode],data,unit,fixLenBuffer) - + if mode == 4: + # variable = "humidity_abs" + unit = "°C" + raw_temp = bme280.get_temperature() # get °C from BME280 sensor + raw_temp_k = 273.15 + raw_temp; # convert sensor temp from degC to K + now_pressure = bme280.get_pressure() # get hPa from BME280 sensor + now_pressure_pa = now_pressure * 100; # convert sensor pressure from hPa to Pa + now_humidity = bme280.get_humidity() # get % relative humidity from BME280 sensor + now_humidity_dpt = rel_to_dpt(raw_temp_k,now_pressure_pa,now_humidity); # calc K dpt humidity + now_humidity_dpt_c = now_humidity_dpt - 273.15; # convert K to °C dpt humidity + data = now_humidity_dpt_c; + # print('DEBUG:raw_temp:' + str(raw_temp)); + # print('DEBUG:raw_temp_k:' + str(raw_temp_k)); + # print('DEBUG:now_pressure:' + str(now_pressure)); + # print('DEBUG:now_pressure_pa:' + str(now_pressure_pa)); + # print('DEBUG:now_humidity:' + str(now_humidity)); + # print('DEBUG:now_humidity_dpt_c:' + str(now_humidity_dpt_c)); + display_text2(variables[mode],data,unit,fixLenBuffer) + + if mode == 5: # variable = "light" unit = "Lux" if proximity < 10: -- 2.30.2