def test_value_range_over_temperature_percent(self):
# Test with +- the same ppm input
self.assertEqual(str(value_range_over_temperature("1 kΩ", "1 %")),
str(ValueRange(350, 1650, "Ω")))
# Test with +- the same ppm input
self.assertEqual(str(value_range_over_temperature("1 kΩ", "1.006 %")),
str(ValueRange(346, 1654, "Ω")))
def test_value_range_over_temperature2(self):
# Test with +- the same ppm input
self.assertEqual(
str(value_range_over_temperature("1 kΩ", ("-100 ppm", "100 ppm"))),
str(ValueRange(994, 1006, "Ω")))
# Test with ++ the same ppm input
self.assertEqual(
str(value_range_over_temperature("1 kΩ",
("+100 ppm", "+100 ppm"))),
str(ValueRange(994, 1006, "Ω")))
def test_value_range_over_temperature_tolerance(self):
# Test with +- the same ppm input
self.assertEqual(
str(value_range_over_temperature("1 kΩ", "100 ppm",
tolerance="1%")),
str(ValueRange(984, 1017, "Ω")))
# Test with ++ the same ppm input
self.assertEqual(
str(
value_range_over_temperature("1 kΩ", ("-100 ppm", "+100 ppm"),
tolerance=("-0%", "+1%"))),
str(ValueRange(994, 1017, "Ω")))
def value_range_over_tolerance(nominal, tolerance="1 %"):
"""
Compute the minimum and maximum value of a given component,
given its nominal value and its tolerance.
"""
normalized = normalize(nominal)
nominal, unit = normalized.value, normalized.unit
# Parse static tolerance
min_tol_coeff, max_tol_coeff, nix = normalize_minmax_tuple(tolerance, name="tolerance")
tol_neg_factor = 1. + min_tol_coeff
tol_pos_factor = 1. + max_tol_coeff
return ValueRange(tol_neg_factor * nominal, tol_pos_factor * nominal, unit)
def value_range_over_temperature(nominal,
coefficient="100ppm",
tolerance="0 %",
tmin="-40 °C",
tmax="85 °C",
tref="25 °C",
significant_digits=4):
"""
Given a component which has a nominal value (e.g. "1 kΩ")
at tref (typically "25 °C") and a coefficient of temperature (e.g. "100ppm").
Computes the mininimum and maximum possible value of that component
over the entire temperature range.
Optionally, a component tolerance can be given (defaults to "0 %")
to also account for static (temperature-independent) differences.
Note that the tolerance is applied to the nominal value before
applying the temperature coefficient.
The min/max values are computed in accordance with MIL-STD-202 method 304.
The coefficient and static tolerance can be given as number or as string
e.g. as ppm, ppb or %
and is interpreted as "plus-minus" value.
Alternatively, it can be given as a 2-tuple indicating separate "+"
and "-" values (e.g. ("-30 ppm", "100 ppm")).
Note that the negative value has to be negative if there is a
negative temperature coefficient!
Usage example:
Keyword arguments
-----------------
nominal : number or string
The nominal value of the component e.g. 1023 or "1.023 kΩ"
coefficient : number or string or 2-tuple (see above)
The temperature coefficient of the component per °C
e.g. "100 ppm", "1 %" or 100e-6
or: ("-30 ppm", "100 ppm") (separate + and - values)
tolerance : number or string or 2-tuple (see above)
The static (temperature-independent) tolerance of the component.
e.g. "100 ppm", "1 %" or 100e-6
or: ("-0.5 %", "1.0%") (separate + and - values)
tmin : number or string
The minimum temperature to consider in °C, e.g. "-40 °C". or -40 or "100 K"
Numbers are interpreted as °C, strings are automatically converted.
tmax : number or string
The maximum temperature to consider in °C, e.g. "85 °C". or 85 or "300 K".
Numbers are interpreted as °C, strings are automatically converted.
tref : number or string
The temperature at which the nominal value was measured, i.e. the "reference temperature".
MIL-STD-202G specifies this as 25°C.
If not specified in the component datasheet, this is usually "20 °C" or "25 °C".
Numbers are interpreted as °C, strings are automatically converted.
significant_digits : integer
How many significant digits to show in the resulting value strings
Returns
-------
A ValueRange() instance containing strings with the correct unit, if any.
Example: ValueRange("99.5 Ω", "100.5 Ω")
Use .min and .max to get the min/max value
"""
# NOTE: These will be in Kelvin after normalization!
tmin = normalize_temperature(tmin)
tmax = normalize_temperature(tmax)
tref = normalize_temperature(tref)
# Static tolerance
# We are only interested in the maximum temperature
# differential from tmin
tdelta_neg = tmin - tref
tdelta_pos = tmax - tref
normalized = normalize(nominal)
nominal, unit = normalized.value, normalized.unit
# Compute nominal factors by static tolerance
tol_min_value, tol_max_value, _ = value_range_over_tolerance(
nominal, tolerance)
# Parse coefficient
min_coeff, max_coeff, _ = normalize_minmax_tuple(coefficient,
name="coefficient")
# NOTE: Minimum & maximum value could be any of those (?)
args = [
tol_min_value * (1. + (tdelta_neg * min_coeff)),
tol_max_value * (1. + (tdelta_neg * min_coeff)),
tol_min_value * (1. + (tdelta_neg * max_coeff)),
tol_max_value * (1. + (tdelta_neg * max_coeff)),
tol_min_value * (1. + (tdelta_pos * min_coeff)),
tol_max_value * (1. + (tdelta_pos * min_coeff)),
tol_min_value * (1. + (tdelta_pos * max_coeff)),
tol_max_value * (1. + (tdelta_pos * max_coeff))
]
min_temp = min(args)
max_temp = max(args)
return ValueRange(min_temp, max_temp, unit, significant_digits)
def test_value_range_over_temperature1(self):
# Test with simple ppm input
assert (str(value_range_over_temperature("1 kΩ", "100 ppm")),
str(ValueRange(994, 1006, "Ω")))
def test_value_range_over_temperature_zero(self):
# Test with simple ppm input
assert (str(value_range_over_temperature("1 kΩ", "0 ppm")),
str(ValueRange(1000, 1000, "Ω")))
def test_value_range_over_temperature3(self):
# Test with +- the same ppm input
assert_equal(
str(value_range_over_temperature("1 kΩ", ("0 ppm", "100 ppm"))),
str(ValueRange(994, 1006, "Ω")))
def test_value_range_over_tolerance(self):
# Test with simple ppm input
self.assertEqual(str(value_range_over_tolerance("1 kΩ", "1 %")),
str(ValueRange(990, 1010, "Ω")))
self.assertEqual(str(value_range_over_tolerance("1 kΩ", "1000 ppm")),
str(ValueRange(999., 1001.0, "Ω")))
