eecalpy 0.9.4

collection of classes for simple to complex electrical calculations

# eecalpy Python module

[](https://badge.fury.io/py/eecalpy) [](https://travis-ci.org/wese3112/eecalpy)

The Electrical Engineering Calculations for Python module is a collection of classes for simple to complex electrical calculations, with a special focus on handling tolerances.

USE AT OWN RISK, I DO NOT GUARANTEE THE CORRECTNESS OF THE CALCULATIONS IN THIS PACKAGE

## Installation

The eecalpy package is available on the Python Package Index (PyPI). The package needs Python 3+, you can install it with:

$ pip install eecalpy

## Introduction

Check out the voltage divider below. For both resistors their tolerance and the temperature coefficient α are given (α in parts per million).


Let’s create two variables for them.

>>> r1 = R(resistance=1000, tolerance=0.05, alpha_ppm=250)
>>> r2 = R(2e3, 0.01, 100)
>>> r1; r2
1.0kΩ ± 5.0% (± 50.0Ω) [0.9500 .. 1.0500]kΩ @ 20°C α=250ppm
2.0kΩ ± 1.0% (± 20.0Ω) [1.9800 .. 2.0200]kΩ @ 20°C α=100ppm

The formula for the voltage divider factor is r1 / (r1 + r2). To calculate it use R.voltage_divider(other_resistor):

>>> r1.voltage_divider(r2)
0.33 ± 4.0% [0.3199 .. 0.3465]

You can also use a shorthand notation:

>>> r1 // r2
0.33 ± 4.0% [0.3199 .. 0.3465]

Attention: Do not use the statement r1 / (r1 + r2) here, because it would use the tolerance limits of r1 twice (addition and division) and therefore yield a false result.

The result above is an instance of the Factor class. Now only the voltage is missing. These are created using U(voltage, tolerance=0.0).

Let’s assume the input voltage is 24V with a 1% tolerance the output voltage of the voltage divider then is:

>>> vin = U(24, 0.01)
>>> vout = r1 // r2 * vin
>>> vout
8.0V ± 5.0% (± 400.0mV) [7.6000 .. 8.4000]V

Note: the statement vout = vin * r1 // r2 does not work. It’s evaluated from left to right, so python first tries vin * r1 which is not implemented (voltage times resistance), but you can always use parenthesis:

>>> vin * (r1 // r2)
8.0V ± 5.0% (± 400.0mV) [7.6000 .. 8.4000]V

For demonstration, let’s calculate some of the voltage divider parameters.

Current through R1 and R2 (to GND):

>>> vin / (r1 + r2)
8.01mA ± 3.33% (± 266.81µA) [7.7394 .. 8.2730]mA

Power dissipation of the resistors:

>>> vout**2 / r1
65.46mW ± 21.35% (± 13.97mW) [51.4842 .. 79.4301]mW
>>> (vin - vout)**2 / r2
128.26mW ± 12.3% (± 15.78mW) [112.4776 .. 144.0351]mW

Let’s also see how vout changes when the ambient temperature is 200°C:

>>> r1.at_T(200) // r2.at_T(200) * vin
8.14V ± 4.97% (± 404.16mV) [7.7359 .. 8.5443]V

R.at_T(temperature) is the same as R.at_temperature(temperature). It returns a new resistor object at the given temperature (in °C).

You can of course also use perfect values, so without the tolerance and temperature coefficient:

>>> r1 = R(1e3)
>>> r2 = R(2e3)
>>> vin = U(24)
>>> r1; r2; vin
1.0kΩ @ 20°C
2.0kΩ @ 20°C
24.0V
>>> vout = r1 / (r1 + r2) * vin
>>> vout
8.0V

By the way, you can get the series resistance using + and the parallel resistance using |:

>>> r1 + r2
3.0kΩ @ 20°C
>>> r1 | r2
666.67Ω @ 20°C
>>> r1 | (R(5e3) + R(3e3)) | r2  # complex statements allowed!
615.38Ω @ 20°C

## Classes

The available classes are:

• Voltage U(voltage, tolerance=0.0)

• Resistance R(resistance, tolerance=0.0, alpha_ppm=None)

• Current I(current, tolerance=0.0)

• Power P(power, tolerance=0.0)

• Factor Factor(factor, tolerance) (unitless factor, example below)

• squared Voltage (V²) Usq(voltage, tolerance=0.0)

• squared Current (A²) Isq(voltage, tolerance=0.0)

All classes do have the following members (example when using a voltage):

>>> v1 = U(24, 0.04)
>>> v1
24.0V ± 4.0% (± 960.0mV) [23.0400 .. 24.9600]V
>>> v1.value
24
>>> v1.min
23.04
>>> v1.max
24.96
>>> v1.unit
'V'

A unit can also be created using the .from_min_max(min, max) classmethod when the lower and upper limit is known (min/max):

>>> P.from_min_max(3, 4)
3.5W ± 14.29% (± 500.0mW) [3.0000 .. 4.0000]W

All units feature the add, subtract, multiply and divide operators. The calculation only works if the result’s type is one of the classes above:

This works because the result type is one of the known classes:

>>> U(10) + U(20)
30.0V
>>> I(2e-3) - I(10e-3)
-8.0mA
>>> U(10) * I(2e-3)
20.0mW
>>> U(10) / I(2e-3)
5.0kΩ @ 20°C
>>> U(10) * Factor(2)
20.0V
>>> I(10e-3) * R(150)
1.5V
>>> P(200) / U(5)
40.0A
>>> U(3) * U(3)
9.0V²
>>> U(3)**2  # U squared
9.0V²
>>> U(3)**2 / R(1e3)
9.0mW

This does not work because voltage divided by power is not a known class:

>>> U / P
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for /: 'type' and 'type'