def tas2ssec(tas, alt, oat, ias, speed_units=default_speed_units, alt_units=default_alt_units, temp_units=default_temp_units, press_units = default_press_units):
"""
Return static source position error as speed error, pressure error and altitude error at sea level.
Returns delta_Vpc, delta_Ps, delta_Hpc and Vc
delta_Vpc = error in airspeed = calibrated airspeed - indicated airspeed corrected for instrument error
delta_Ps = error in the pressure sensed by the static system = pressure sensed in the static system - ambient pressure
delta_Hpc = altitude error at sea level = actual altitude - altitude sensed by the static system
Vc = calibrated airspeed at the test point
"""
P0 = U.press_conv(constants.P0, from_units = 'pa', to_units = press_units)
cas = A.tas2cas(tas, alt, oat, speed_units=speed_units, alt_units=alt_units, temp_units=temp_units)
delta_Vpc = cas - ias
qcic = A.cas2dp(ias, speed_units=speed_units, press_units =press_units)
qc = A.cas2dp(cas, speed_units=speed_units, press_units = press_units)
delta_Ps = qc - qcic
delta_Hpc = SA.press2alt(P0 - delta_Ps, press_units = press_units)
# print 'Vc = %.1f, delta_vpc = %.1f, delta_ps = %.1f, delta_hpc = %.0f' % (cas, delta_Vpc, delta_Ps, delta_Hpc)
return delta_Vpc, delta_Ps, delta_Hpc, cas
def press2alt(P, press_units=default_press_units,
alt_units=default_alt_units):
"""
Return the altitude corresponding to the specified pressure, with
pressure in inches of HG, mm of HG, psi, psf (lb per sq. ft), pa, hpa or
mb.
The altitude is in units of feet ('ft'), metres ('m'), statute miles,
('sm') or nautical miles ('nm')
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure altitude in feet for a pressure of 31.0185 inches
of HG:
>>> press2alt(31.0185)
-999.98992888235091
Calculate the pressure altitude in feet for a pressure of
1455.33 lb sq. ft:
>>> press2alt(1455.33, press_units = 'psf')
10000.002466564831
Calculate the pressure altitude in metres for a pressure of
90.3415 mm HG:
>>> press2alt(90.3415, press_units = 'mm HG', alt_units = 'm')
15000.025465320754
Calculate the pressure altitude in metres for a pressure of
1171.86 pascal:
>>> press2alt(1171.86, press_units = 'pa', alt_units = 'm')
30000.029510365184
"""
# function tested in tests/test_std_atm.py
P = U.press_conv(P, from_units=press_units, to_units='in HG')
if P > P11:
H = _press2alt_gradient(P, P0, 0, T0, L0)
elif P > P20:
H = _press2alt_isothermal(P, P11, 11, T11)
elif P > P32:
H = _press2alt_gradient(P, P20, 20, T20, L20)
elif P > P47:
H = _press2alt_gradient(P, P32, 32, T32, L32)
elif P > P51:
H = _press2alt_isothermal(P, P47, 47, T47)
elif P > P71:
H = _press2alt_gradient(P, P51, 51, T51, L51)
else:
H = _press2alt_gradient(P, P71, 71, T71, L71)
if H > 84.852:
raise ValueError, \
'This function is only implemented for altitudes of 84.852 km and below.'
return U.len_conv(H, from_units='km', to_units=alt_units)
def press2alt(P, press_units=default_press_units, alt_units=default_alt_units):
"""
Return the altitude corresponding to the specified pressure, with
pressure in inches of HG, mm of HG, psi, psf (lb per sq. ft), pa, hpa or
mb.
The altitude is in units of feet ('ft'), metres ('m'), statute miles,
('sm') or nautical miles ('nm')
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure altitude in feet for a pressure of 31.0185 inches
of HG:
>>> press2alt(31.0185)
-999.98992888235091
Calculate the pressure altitude in feet for a pressure of
1455.33 lb sq. ft:
>>> press2alt(1455.33, press_units = 'psf')
10000.002466564831
Calculate the pressure altitude in metres for a pressure of
90.3415 mm HG:
>>> press2alt(90.3415, press_units = 'mm HG', alt_units = 'm')
15000.025465320754
Calculate the pressure altitude in metres for a pressure of
1171.86 pascal:
>>> press2alt(1171.86, press_units = 'pa', alt_units = 'm')
30000.029510365184
"""
# function tested in tests/test_std_atm.py
P = U.press_conv(P, from_units=press_units, to_units='in HG')
if P > P11:
H = _press2alt_gradient(P, P0, 0, T0, L0)
elif P > P20:
H = _press2alt_isothermal(P, P11, 11, T11)
elif P > P32:
H = _press2alt_gradient(P, P20, 20, T20, L20)
elif P > P47:
H = _press2alt_gradient(P, P32, 32, T32, L32)
elif P > P51:
H = _press2alt_isothermal(P, P47, 47, T47)
elif P > P71:
H = _press2alt_gradient(P, P51, 51, T51, L51)
else:
H = _press2alt_gradient(P, P71, 71, T71, L71)
if H > 84.852:
print(
'This function is only implemented for altitudes of 84.852 km and below.'
)
return U.len_conv(H, from_units='km', to_units=alt_units)
def test_07(self):
Value = U.press_conv(1, from_units='psi', to_units='cm H2O')
Truth = 1 / .014198 # truth value from NASA RP 1046 Table A27.
# Note that there is an inconsistency between
# the stated conversions from psi to cm H2O
# (70.376), and the conversion from cm H2O to
# psi (.014198)
print(('Truth=%.8f, Value=%.8f' % (Truth, Value)))
self.assertTrue(RE(Value, Truth) <= 5e-5)
def test_07(self):
Value = U.press_conv(1, from_units='psi', to_units='cm H2O')
Truth = 1/.014198 # truth value from NASA RP 1046 Table A27.
# Note that there is an inconsistency between
# the stated conversions from psi to cm H2O
# (70.376), and the conversion from cm H2O to
# psi (.014198)
print('Truth=%.8f, Value=%.8f' % (Truth, Value))
self.failUnless(RE(Value, Truth) <= 5e-5)
def pressure_alt(H, alt_setting, alt_units=default_alt_units):
"""
Return the pressure altitude, given the barometric altitude and the
altimeter setting.
Altimeter setting may have units of inches of HG, or hpa or mb. If the
altimeter setting value is less than 35, the units are assumed to be
in HG, otherwise they are assumed to be hpa. The altimeter setting must
be in the range of 25 to 35 inches of mercury.
The altitude may have units of feet ('ft'), metres ('m'), statute miles,
('sm') or nautical miles ('nm').
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure altitude for 1,000 (default altitude units)
barometric altitude with altimeter setting of 30.92 in HG:
>>> pressure_alt(1000, 30.92)
88.6424431787118
Calculate the pressure altitude for 1,000 (default altitude units)
barometric altitude with altimeter setting of 1008 mb:
>>> pressure_alt(1000, 1008)
1143.679844292918
Calculate the pressure altitude in metres for 304.8 m barometric
altitude with altimeter setting of 1008 mb:
>>> pressure_alt(304.8, 1008, alt_units = 'm')
348.59361654048143
"""
H = U.length_conv(H, from_units=alt_units, to_units='ft')
if alt_setting > 35:
alt_setting = U.press_conv(alt_setting,
from_units='hpa',
to_units='in HG')
if alt_setting < 25 or alt_setting > 35:
raise ValueError('Altimeter setting out of range.')
base_press = U.press_conv(P0, from_units='pa', to_units='in HG')
HP = H + 145442.2 * (1 - (alt_setting / base_press)**0.190261)
HP = U.length_conv(HP, from_units='ft', to_units=alt_units)
return HP
def pressure_alt(H, alt_setting, alt_units=default_alt_units):
"""
Return the pressure altitude, given the barometric altitude and the
altimeter setting.
Altimeter setting may have units of inches of HG, or hpa or mb. If the
altimeter setting value is less than 35, the units are assumed to be
in HG, otherwise they are assumed to be hpa. The altimeter setting must
be in the range of 25 to 35 inches of mercury.
The altitude may have units of feet ('ft'), metres ('m'), statute miles,
('sm') or nautical miles ('nm').
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure altitude for 1,000 (default altitude units)
barometric altitude with altimeter setting of 30.92 in HG:
>>> pressure_alt(1000, 30.92)
88.642443178711801
Calculate the pressure altitude for 1,000 (default altitude units)
barometric altitude with altimeter setting of 1008 mb:
>>> pressure_alt(1000, 1008)
1143.679844292918
Calculate the pressure altitude in metres for 304.8 m barometric
altitude with altimeter setting of 1008 mb:
>>> pressure_alt(304.8, 1008, alt_units = 'm')
348.59361654048143
"""
H = U.length_conv(H, from_units=alt_units, to_units='ft')
if alt_setting > 35:
alt_setting = U.press_conv(alt_setting, from_units='hpa',
to_units='in HG')
if alt_setting < 25 or alt_setting > 35:
raise ValueError('Altimeter setting out of range.')
base_press = U.press_conv(P0, from_units='pa', to_units='in HG')
HP = H + 145442.2 * (1 - (alt_setting / base_press) ** 0.190261)
HP = U.length_conv(HP, from_units='ft', to_units=alt_units)
return HP
def QNH(
HP,
H,
alt_units=default_alt_units,
alt_setting_units='in HG',
):
"""
Return the altimeter setting, given the pressure altitude (HP) and the
barometric altitude (H).
"""
HP = U.len_conv(HP, from_units=alt_units, to_units='ft')
H = U.len_conv(H, from_units=alt_units, to_units='ft')
QNH = P0 * (1 - (HP - H) / 145442.2)**5.255594
QNH = U.press_conv(QNH, from_units='in HG', to_units=alt_setting_units)
return QNH
def QNH(
HP,
H,
alt_units=default_alt_units,
alt_setting_units='in HG',
):
"""
Return the altimeter setting, given the pressure altitude (HP) and the
barometric altitude (H).
"""
HP = U.length_conv(HP, from_units=alt_units, to_units='ft')
H = U.length_conv(H, from_units=alt_units, to_units='ft')
QNH = P0 * (1 - (HP - H) / 145442.2) ** 5.255594
QNH = U.press_conv(QNH, from_units='in HG',
to_units=alt_setting_units)
return QNH
def alt2press(H,
alt_units=default_alt_units,
press_units=default_press_units):
"""
Return the atmospheric pressure for a given altitude, with the
altitude in feet ('ft'), metres ('m'), statute miles, ('sm') or nautical
miles ('nm'), and the pressure in inches of HG ('in HG'), mm of HG
('mm HG'), psi, lb per sq. ft ('psf'), pa, hpa or mb.
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure in inches of mercury at 5,000 (default altitude
units):
>>> alt2press(5000)
24.895961289464015
Calculate the pressure in pounds per square foot at 10,000 (default
altitude units):
>>> alt2press(10000, press_units = 'psf')
1455.3301392981359
Calculate the pressure in pascal at 20 km:
>>> alt2press(20, press_units = 'pa', alt_units = 'km')
5474.8827144576408
"""
# uses meters, inches of HG and degrees K for the internal calculations
# function tested in tests/test_std_atm.py
H = U.len_conv(H, from_units=alt_units, to_units='m')
press = P0 * alt2press_ratio(H, alt_units='m')
press = U.press_conv(press, from_units='in HG',
to_units=press_units)
return press
def tas2ssec(tas,
alt,
oat,
ias,
speed_units=default_speed_units,
alt_units=default_alt_units,
temp_units=default_temp_units,
press_units=default_press_units):
"""
Return static source position error as speed error, pressure error and altitude error at sea level.
Returns delta_Vpc, delta_Ps, delta_Hpc and Vc
delta_Vpc = error in airspeed = calibrated airspeed - indicated airspeed corrected for instrument error
delta_Ps = error in the pressure sensed by the static system = pressure sensed in the static system - ambient pressure
delta_Hpc = altitude error at sea level = actual altitude - altitude sensed by the static system
Vc = calibrated airspeed at the test point
"""
P0 = U.press_conv(constants.P0, from_units='pa', to_units=press_units)
cas = A.tas2cas(tas,
alt,
oat,
speed_units=speed_units,
alt_units=alt_units,
temp_units=temp_units)
delta_Vpc = cas - ias
qcic = A.cas2dp(ias, speed_units=speed_units, press_units=press_units)
qc = A.cas2dp(cas, speed_units=speed_units, press_units=press_units)
delta_Ps = qc - qcic
delta_Hpc = SA.press2alt(P0 - delta_Ps, press_units=press_units)
# print 'Vc = %.1f, delta_vpc = %.1f, delta_ps = %.1f, delta_hpc = %.0f' % (cas, delta_Vpc, delta_Ps, delta_Hpc)
return delta_Vpc, delta_Ps, delta_Hpc, cas
def alt2press(H, alt_units=default_alt_units, press_units=default_press_units):
"""
Return the atmospheric pressure for a given altitude, with the
altitude in feet ('ft'), metres ('m'), statute miles, ('sm') or nautical
miles ('nm'), and the pressure in inches of HG ('in HG'), mm of HG
('mm HG'), psi, lb per sq. ft ('psf'), pa, hpa or mb.
If the units are not specified, the units in default_units.py are used.
Examples:
Calculate the pressure in inches of mercury at 5,000 (default altitude
units):
>>> alt2press(5000)
24.895961289464015
Calculate the pressure in pounds per square foot at 10,000 (default
altitude units):
>>> alt2press(10000, press_units = 'psf')
1455.3301392981359
Calculate the pressure in pascal at 20 km:
>>> alt2press(20, press_units = 'pa', alt_units = 'km')
5474.8827144576408
"""
# uses meters, inches of HG and degrees K for the internal calculations
# function tested in tests/test_std_atm.py
H = U.len_conv(H, from_units=alt_units, to_units='m')
press = P0 * alt2press_ratio(H, alt_units='m')
press = U.press_conv(press, from_units='in HG', to_units=press_units)
return press
def test_02(self):
Value = U.press_conv(1, from_units='mm HG', to_units='psi')
Truth = 0.01934543333
self.failUnless(RE(Value, Truth) <= 5e-4)
def test_05(self):
Value = U.press_conv(1, from_units='cm H2O', to_units='in H2O')
Truth = 1 / 2.54
self.assertTrue(RE(Value, Truth) <= 4e-5)
def tas2ssec2(tas,
ind_alt,
oat,
ias,
std_alt=0,
speed_units=default_speed_units,
alt_units=default_alt_units,
temp_units=default_temp_units,
press_units=default_press_units):
"""
Return static source position error as speed error, pressure error and
altitude error at sea level using speed course method.
Returns delta_Vpc, delta_Ps and delta_Hpc
tas = true airspeed determined by speed course method, or GPS
ind_alt = pressure altitude, corrected for instrument error
oat = outside air temperature, corrected for instrument error and ram temperature rise
ias = indicated airspeed, corrected for instrument error
std_alt = altitude to provide delta_Hpc for
delta_Vpc = error in airspeed = calibrated airspeed - indicated airspeed
corrected for instrument error
delta_Ps = error in the pressure sensed by the static system = pressure
sensed in the static system - ambient pressure
delta_Hpc = altitude error at std_alt = actual altitude - altitude
sensed by the static system
Uses analysis method from USAF Test Pilot School. Unlike some other
methods (e.g.. that in FAA AC 23-8B, or NTPS GPS_PEC.xls), this method
provides an exact conversion from TAS to CAS (some other methods assume
CAS = EAS), and it accounts for the effect of position error of altitude
on the conversion from TAS to CAS (some other methods assume pressure
altitude = indicated pressure altitude).
"""
tas = U.speed_conv(tas, speed_units, 'kt')
ind_alt = U.length_conv(ind_alt, alt_units, 'ft')
oat = U.temp_conv(oat, temp_units, 'C')
M = A.tas2mach(tas, oat, temp_units='C', speed_units='kt')
if M > 1:
raise ValueError('This method only works for Mach < 1')
delta_ic = SA.alt2press_ratio(ind_alt, alt_units='ft')
qcic_over_Psl = A.cas2dp(ias, speed_units='kt',
press_units=press_units) / U.press_conv(
constants.P0, 'pa', to_units=press_units)
qcic_over_Ps = qcic_over_Psl / delta_ic
Mic = A.dp_over_p2mach(qcic_over_Ps)
delta_mach_pc = M - Mic
if Mic > 1:
raise ValueError('This method only works for Mach < 1')
deltaPp_over_Ps = (1.4 * delta_mach_pc * (Mic + delta_mach_pc / 2)) / (
1 + 0.2 * (Mic + delta_mach_pc / 2)**2)
deltaPp_over_qcic = deltaPp_over_Ps / qcic_over_Ps
delta_Hpc = SA.alt2temp_ratio(
std_alt, alt_units='ft') * deltaPp_over_Ps / 3.61382e-5
# experimental - alternate way to calculate delta_Hpc that gives same answer
Ps = SA.alt2press(ind_alt, alt_units='ft', press_units=press_units)
delta_Ps = deltaPp_over_Ps * Ps
P_std = SA.alt2press(std_alt, alt_units='ft', press_units=press_units)
deltaPs_std = deltaPp_over_Ps * P_std
delta_Hpc2 = SA.press2alt(P_std - deltaPs_std,
press_units=press_units) - std_alt
delta_std_alt = SA.alt2press_ratio(std_alt, alt_units='ft')
asl = U.speed_conv(constants.A0, 'm/s', 'kt')
delta_Vpc_std_alt = deltaPp_over_Ps * delta_std_alt * asl**2 / (
1.4 * ias * (1 + 0.2 * (ias / asl)**2)**2.5)
actual_alt = SA.press2alt(Ps + delta_Ps,
press_units=press_units,
alt_units='ft')
cas = A.tas2cas(tas,
actual_alt,
oat,
speed_units='kt',
alt_units='ft',
temp_units='C')
return delta_Vpc, delta_Ps, delta_Hpc, cas
def test_05(self):
Value = U.press_conv(1, from_units='cm H2O', to_units='in H2O')
Truth = 1/2.54
self.failUnless(RE(Value, Truth) <= 4e-5)
def test_06(self):
Value = U.press_conv(1, from_units='in H2O', to_units='mm HG')
Truth = 1.865
print('Truth=%.8f, Value=%.8f' % (Truth, Value))
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_03(self):
Value = U.press_conv(1, from_units='psi', to_units='lb/ft**2')
Truth = 144
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_04(self):
Value = U.press_conv(1, from_units='lb/ft**2', to_units='mb')
Truth = 0.4788
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_01(self):
Value = U.press_conv(1, from_units='in HG', to_units='mm HG')
Truth = 25.4
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_02(self):
Value = U.press_conv(1, from_units='mm HG', to_units='psi')
Truth = 0.01934543333
self.failUnless(RE(Value, Truth) <= 5e-4)
def test_06(self):
Value = U.press_conv(1, from_units='in H2O', to_units='mm HG')
Truth = 1.865
print(('Truth=%.8f, Value=%.8f' % (Truth, Value)))
self.assertTrue(RE(Value, Truth) <= 1e-5)
def test_04(self):
Value = U.press_conv(1, from_units='lb/ft**2', to_units='mb')
Truth = 0.4788
self.failUnless(RE(Value, Truth) <= 1e-5)
def tas2ssec2(tas, ind_alt, oat, ias, std_alt = 0, speed_units=default_speed_units, alt_units=default_alt_units, temp_units=default_temp_units, press_units = default_press_units):
"""
Return static source position error as speed error, pressure error and
altitude error at sea level using speed course method.
Returns delta_Vpc, delta_Ps and delta_Hpc
tas = true airspeed determined by speed course method, or GPS
ind_alt = pressure altitude, corrected for instrument error
oat = outside air temperature, corrected for instrument error and ram temperature rise
ias = indicated airspeed, corrected for instrument error
std_alt = altitude to provide delta_Hpc for
delta_Vpc = error in airspeed = calibrated airspeed - indicated airspeed
corrected for instrument error
delta_Ps = error in the pressure sensed by the static system = pressure
sensed in the static system - ambient pressure
delta_Hpc = altitude error at std_alt = actual altitude - altitude
sensed by the static system
Uses analysis method from USAF Test Pilot School. Unlike some other
methods (e.g.. that in FAA AC 23-8B, or NTPS GPS_PEC.xls), this method
provides an exact conversion from TAS to CAS (some other methods assume
CAS = EAS), and it accounts for the effect of position error of altitude
on the conversion from TAS to CAS (some other methods assume pressure
altitude = indicated pressure altitude).
"""
tas = U.speed_conv(tas, speed_units, 'kt')
ind_alt = U.length_conv(ind_alt, alt_units, 'ft')
oat = U.temp_conv(oat, temp_units, 'C')
M = A.tas2mach(tas, oat, temp_units='C', speed_units='kt')
if M > 1:
raise ValueError, 'This method only works for Mach < 1'
delta_ic = SA.alt2press_ratio(ind_alt, alt_units='ft')
qcic_over_Psl = A.cas2dp(ias, speed_units='kt', press_units=press_units) / U.press_conv(constants.P0, 'pa', to_units=press_units)
qcic_over_Ps = qcic_over_Psl / delta_ic
Mic = A.dp_over_p2mach(qcic_over_Ps)
delta_mach_pc = M - Mic
if Mic > 1:
raise ValueError, 'This method only works for Mach < 1'
deltaPp_over_Ps = (1.4 * delta_mach_pc * (Mic + delta_mach_pc / 2)) / (1 + 0.2 * (Mic + delta_mach_pc / 2 )**2)
deltaPp_over_qcic = deltaPp_over_Ps / qcic_over_Ps
delta_Hpc = SA.alt2temp_ratio(std_alt, alt_units='ft') * deltaPp_over_Ps / 3.61382e-5
# experimental - alternate way to calculate delta_Hpc that gives same answer
Ps = SA.alt2press(ind_alt, alt_units='ft', press_units=press_units)
delta_Ps = deltaPp_over_Ps * Ps
P_std = SA.alt2press(std_alt, alt_units='ft', press_units=press_units)
deltaPs_std = deltaPp_over_Ps * P_std
delta_Hpc2 = SA.press2alt(P_std - deltaPs_std, press_units = press_units) - std_alt
delta_std_alt = SA.alt2press_ratio(std_alt, alt_units='ft')
asl = U.speed_conv(constants.A0, 'm/s', 'kt')
delta_Vpc_std_alt = deltaPp_over_Ps * delta_std_alt * asl**2 / (1.4 * ias * (1 + 0.2 * (ias / asl)**2)**2.5)
actual_alt = SA.press2alt(Ps + delta_Ps, press_units = press_units, alt_units = 'ft')
cas = A.tas2cas(tas, actual_alt, oat, speed_units='kt', alt_units='ft', temp_units='C')
return delta_Vpc, delta_Ps, delta_Hpc, cas
def sat_press(
T='FALSE',
DP='FALSE',
RH=0.0,
temp_units=default_temp_units,
press_units=default_press_units,
):
"""
Return the saturated vapour pressure of water. Either the dew point, or
the temperature and the relative humidity must be specified. If both the
dew point and relative humidity are specified, the relative humidity value
is ignored.
If the temperature and dew point are both specified, the dew point cannot
be greater than the temperature:
If the units are not specified, the units in default_units.py are used.
>>> sat_press(T=10, DP=11)
Traceback (most recent call last):
File '<stdin>', line 1, in <module>
File 'std_atm.py', line 795, in sat_press
raise ValueError, 'The dew point cannot be greater than the temperature.'
ValueError: The dew point cannot be greater than the temperature.
Dew point is 11 deg (default temperature units). Find the water vapour
pressure in default pressure units:
>>> sat_press(DP=11)
0.38741015927568667
Dew point is 65 deg F. Find the water vapour pressure in default pressure units:
>>> sat_press(DP=65, temp_units = 'F')
0.62207710701956165
Dew point is 212 deg F (the boiling point of water at sea level).
Find the water vapour pressure in lb per sq. inch:
>>> sat_press(DP=212, temp_units = 'F', press_units = 'psi')
14.696764873564959
Temperature is 30 deg C. Find the water vapour pressure in default pressure units:
for 50% relative humidity:
>>> sat_press(T=30, RH = 0.5)
0.62647666996057927
"""
if DP != 'FALSE':
# use dew point method
if T != 'FALSE':
if DP > T:
raise ValueError('The dew point cannot be greater than the temperature.')
DP = U.temp_conv(DP, from_units=temp_units, to_units='C')
# calculate vapour pressure
Pv = _sat_press(DP) * 100.
else:
if RH == 'FALSE':
raise ValueError('Either DP (dew point) or RH (relative humidity) must be specified.')
# relative humidity is specified
# confirm relative humidity is in range
if RH < 0 or RH > 1:
raise ValueError('The relative humidity must be in the range of 0 to 1.')
if T == 'FALSE':
raise ValueError('If the relative humidity is specified, the temperature must also be specified.')
T = U.temp_conv(T, from_units=temp_units, to_units='C')
Pv = _sat_press(T) * 100.
Pv *= RH
Pv = U.press_conv(Pv, from_units='pa', to_units=press_units)
return Pv
def test_01(self):
Value = U.press_conv(1, from_units='in HG', to_units='mm HG')
Truth = 25.4
self.failUnless(RE(Value, Truth) <= 1e-5)
def sat_press(
T='FALSE',
DP='FALSE',
RH=0.0,
temp_units=default_temp_units,
press_units=default_press_units,
):
"""
Return the saturated vapour pressure of water. Either the dew point, or
the temperature and the relative humidity must be specified. If both the
dew point and relative humidity are specified, the relative humidity value
is ignored.
If the temperature and dew point are both specified, the dew point cannot
be greater than the temperature:
If the units are not specified, the units in default_units.py are used.
>>> sat_press(T=10, DP=11)
Traceback (most recent call last):
File '<stdin>', line 1, in <module>
File 'std_atm.py', line 795, in sat_press
raise ValueError, 'The dew point cannot be greater than the temperature.'
ValueError: The dew point cannot be greater than the temperature.
Dew point is 11 deg (default temperature units). Find the water vapour
pressure in default pressure units:
>>> sat_press(DP=11)
0.38741015927568667
Dew point is 65 deg F. Find the water vapour pressure in default pressure units:
>>> sat_press(DP=65, temp_units = 'F')
0.62207710701956165
Dew point is 212 deg F (the boiling point of water at sea level).
Find the water vapour pressure in lb per sq. inch:
>>> sat_press(DP=212, temp_units = 'F', press_units = 'psi')
14.696764873564959
Temperature is 30 deg C. Find the water vapour pressure in default pressure units:
for 50% relative humidity:
>>> sat_press(T=30, RH = 0.5)
0.62647666996057927
"""
if DP != 'FALSE':
# use dew point method
if T != 'FALSE':
if DP > T:
print('The dew point cannot be greater than the temperature.')
DP = U.temp_conv(DP, from_units=temp_units, to_units='C')
# calculate vapour pressure
Pv = _sat_press(DP) * 100
else:
if RH == 'FALSE':
print(
'Either DP (dew point) or RH (relative humidity) must be specified.'
)
# relative humidity is specified
# confirm relative humidity is in range
if RH < 0 or RH > 1:
print('The relative humidity must be in the range of 0 to 1.')
if T == 'FALSE':
print(
'If the relative humidity is specified, the temperature must also be specified.'
)
T = U.temp_conv(T, from_units=temp_units, to_units='C')
Pv = _sat_press(T) * 100
Pv *= RH
Pv = U.press_conv(Pv, from_units='pa', to_units=press_units)
return Pv
def test_03(self):
Value = U.press_conv(1, from_units='psi', to_units='lb/ft**2')
Truth = 144
self.failUnless(RE(Value, Truth) <= 1e-5)
