Class: OhmsLawCalculator

Inherits:
Object
  • Object
show all
Includes:
ActiveModel::Attributes, ActiveModel::Model
Defined in:
lib/ohms_law_calculator.rb

Overview

Solves Ohm's Law (V = I × R) and the power equation (P = V × I) for
whichever of voltage / current / resistance / power is missing, given
any two of the four. Used by the heating-element configuration and
circuit-sizing tools.

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.calc(attributes) ⇒ OhmsLawCalculator

Voltage (V) = Current (I) * Resistance (R)
Power (P) = Voltage (V) * Current (I)

Returns:



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# File 'lib/ohms_law_calculator.rb', line 18

def self.calc(attributes)
  new(attributes).calc
end

.difference_in_percent(number1, number2) ⇒ BigDecimal

Returns the percent difference (100.0 when either side is nil).

Returns:

  • (BigDecimal) —

    the percent difference (100.0 when either side is nil)



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# File 'lib/ohms_law_calculator.rb', line 45

def self.difference_in_percent(number1, number2)
  return 100.0 if number1.nil? || number2.nil?

  d = (BigDecimal((number1 - number2).abs) / number1) * 100
  d.round(1)
end

.validate(attributes, tolerance: 5.0) ⇒ Array<String>

Returns validation error messages (empty when valid).

Returns:

  • (Array<String>) —

    validation error messages (empty when valid)



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# File 'lib/ohms_law_calculator.rb', line 23

def self.validate(attributes, tolerance: 5.0)
  attributes.dup
  orig_resistance = attributes[:resistance]
  orig_voltage = attributes[:voltage]
  orig_current = attributes[:current]
  orig_power = attributes[:power]
  calc = new(attributes).calc
  resistance_diff = difference_in_percent(calc.resistance, orig_resistance)
  voltage_diff = difference_in_percent(calc.voltage, orig_voltage)
  current_diff = difference_in_percent(calc.current, orig_current)
  power_diff = difference_in_percent(calc.power, orig_power)

  # compare
  errors = []
  errors << "Resistance (Ohm) invalid. #{orig_resistance || 'nil'} different than calculated  #{calc.resistance} by #{resistance_diff} %" if resistance_diff > tolerance
  errors << "Voltage invalid. #{orig_voltage || 'nil'} different than calculated #{calc.voltage} by #{voltage_diff} %" if voltage_diff > tolerance
  errors << "Current (Amps) invalid. #{orig_current || 'nil'} different than calculated #{calc.current} by #{current_diff} %" if current_diff > tolerance
  errors << "Power (Watts) invalid. #{orig_power || 'nil'} different than calculated #{calc.power} by #{power_diff}" if power_diff > tolerance
  errors
end

Instance Method Details

#calc ⇒ Object

Returns the last computed attribute value.

Returns:

  • (Object) —

    the last computed attribute value



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# File 'lib/ohms_law_calculator.rb', line 53

def calc
  Rails.logger.debug { "Ohms Law Calculator Inputs: #{attributes.inspect}" }
  if voltage && current
    self.resistance = BigDecimal(voltage) / current
    self.power = (voltage * current).round
  elsif voltage && resistance
    self.current = BigDecimal(voltage) / resistance
    self.power = (BigDecimal(voltage**2) / resistance).round
  elsif voltage && power
    self.current = BigDecimal(power) / voltage
    self.resistance = BigDecimal(voltage**2) / power
  elsif current && resistance
    self.voltage = current * resistance
    self.power = ((current**2) * resistance).round
  elsif current && power
    self.voltage = BigDecimal(power) / current
    self.resistance = BigDecimal(power) / (current**2)
  elsif resistance && power
    self.voltage = Math.sqrt(power * resistance)
    self.current = Math.sqrt(BigDecimal(watts) / ohms)
  elsif voltage
    self.current = nil
    self.power = nil
    self.resistance = nil
  elsif current
    self.voltage = nil
    self.power = nil
    self.resistance = nil
  elsif resistance
    self.voltage = nil
    self.current = nil
    self.power = nil
  elsif power
    self.voltage = nil
    self.current = nil
    self.resistance = nil
  end
  self.power = power&.round
  self.voltage = voltage&.round
  self.current = current&.round(4)
  self.resistance = resistance&.round(5)
  OpenStruct.new(attributes.symbolize_keys).freeze
end