PSM Pulse Width Modulation (PWM) Function Scope, Basic Function - GF54.21-S-1014A

Model All (Light transporter) 

Definitions:

PWM (pulse width modulation)

Overview 

This document contains information on:

• General 
• Function 
  • PWM functions (PWM output) 
  • Signal "Display dimming (PWM)" 
  • Signal "Vehicle speed (PWM)" 
  • Signal "motor speed (PWM)" 
  • Signal "Interior temperature (PWM)" 
  • Signal "Outside temperature (PWM)" 
  • Signal "Wheel speed (PWM)" 
  • Signal "PWM function test" 
  • Freely parameterizable pulse width modulated signal for PWM-compatible outputs 

General 

Pulse width modulation (PWM) is a type of digital modulation, in which a technical size (e.g. electric voltage) changes between two values. PWM is primarily used in control and regulation technology.

Function 

PWM functions (PWM output) 

Signal "Tml. 58d (PWM)":

The signal "Tml. 58d (PWM)" from the instrument cluster can be output as a pulse width modulated signal at the PWM-capable output. If no signal is received, 0 % is output.

Signal "Display dimming (PWM)" 

The signal "Display dimming (PWM)" from the instrument cluster can be output as a pulse width modulated signal at the PWM-capable output.

Upon reception of an invalid "Display dimming (PWM)" signal from instrument cluster, 70 % is output. If the "Display dimming (PWM)" signal changes, the new percentage is set using a ramp in order to prevent a sudden change in the display dimming. The parameters can be set via menu item "Interfaces → CAN bus → Miscellaneous → Properties".

The following two parameters are available:

• Time for dimming of instrument illumination:
  • Time in 10 ms steps that determines the duration of the ramp.
• Brightness of instrument illumination:
  • Change in percent per ramp step

Output of the signal depends on the status of circuit 15R.

With "Circuit 15R ON", the output value is determined by the status of the standing lights. If the standing lights are switched on, the previously set value is retained. If the standing lights are switched off, 70 % are actuated.

Signal "Vehicle speed (PWM)" 

The signal "Vehicle speed (PWM)" from the instrument cluster can be output as a pulse width modulated signal at the PWM-capable output.

If no signal is received, no pulses are output.

The output of the signal depends on tml. 15. No pulses are output if the status is "Tml. 15 OFF".

The following formula applies for converting the vehicle speed into pulses:

• Pulses (1/s) = (speed (km/h) x 4 (pulse/m)) ÷ 3.6

Signal "motor speed (PWM)" 

The signal "Engine speed (PWM)" from the electronic ignition lock control unit (EZS) can be output as a pulse width modulated signal at the PWM-capable output. If no signal is received, no pulses are output.

The output of the pulses can be set with the "K-Factor" parameter using the menu item "Interfaces → Outputs → Assignment of pulse width modulated signals to PSM-capable outputs → Properties → Default PWM signals". This parameter determines how many pulses are output per revolution. The default value is 1 pulse per revolution.

The following formula applies for converting the motor speed into pulses:

• Pulses (1/s) = K-Factor x Engine speed (rpm) ÷ 60

Signal "Interior temperature (PWM)" 

The signal "Vehicle interior temperature (PWM)" from the air conditioning system can be output as a pulse width modulated signal at the PWM-capable output.

If no signal is received, no pulses are output.

Output of the signal depends on whether the air conditioning system is installed. If an air conditioning system is not installed, 100 % is output.

The following formula applies for converting the interior temperature into the percentage (duty cycle) for PWM output:

• Duty cycle = (vehicle interior temperature (°C) x 4) ÷ 232°C

Signal "Outside temperature (PWM)" 

The signal "Outside temperature (PWM)" from the instrument cluster can be output as a pulse width modulated signal at the PWM-capable output.

If no signal is received, no pulses are output.

The output of the signal depends on the installation of the outside temperature sensor. If the respective temperature sensor is not installed, 0 % is output.

The following formula applies for converting the outside temperature into the percentage (duty cycle) for PWM output:

• Duty cycle = (outside temperature (°C) + 40°C) ÷ 125°C

Signal "Wheel speed (PWM)" 

The wheel pulse counter can be output as a pulse width modulated signal at the PWM-capable output.

The pulses to be output are calculated every 100 ms. The pulses already output and the current wheel speed are included in the calculation. Including the wheel speed results in more constant output of the pulses when the vehicle is being driven at a constant speed.

Via the backward counting implemented in the hardware of the output pulses it is ensured that no deviation of the output pulses from the specified value occurs. The deviation is limited to a maximum of one pulse per operating cycle.

The following formula applies for converting the current wheel speed into pulses:

• Pulses (1/s) = (wheel speed (rpm) x 48 (pulses/wheel revolution)) ÷ 60

The specified value calculated in this way is then compared with the actual number of pulses so far output and, if necessary, corrected slightly.

Signal "PWM function test" 

The PWM function test makes it possible to output a pulse width modulated signal at the PWM-capable output as a test. This enables the connected system to be tested.

The PWM function test can be selected in a menu item under the "Actuations" tab.

Freely parameterizable pulse width modulated signal for PWM-compatible outputs 

A freely parameterizable pulse width modulated signal can be output at the output using this function module.

The internal inputs of the module can be configured using the menu item "Assignment of pulse width modulated signals at the PWM-capable outputs → Signals". For each PWM-capable output, there is an associated input to which any pulse width modulated signal can be assigned. Furthermore for each PWM-capable output, there is an associated input with which the output can be activated or deactivated via another signal.

The pulse width modulated signals can be adjusted using the menu item "Properties → Freely parameterizable pulse width modulated signals". A frequency or maximum value can be set for each output.

The value range for the parameter "Frequency" is 40.0 to 2000.0 Hz in 0.1 Hz steps.

Using the parameter "Maximum value", it is possible to determine a limit value for the pulse width modulated signal at the input of the module from which the pulse width modulated signal reaches 100 % at the output. If the limit value at the input is exceeded, the pulse width modulated signal at the output remains at 100%.

For all values at the input which are below or equal to the parameterized maximum value, the duty cycle of the PWM output is calculated as per the following formula:

• Duty cycle (%) = (input value/maximum value) x 100 %

The output signal of the signal generator "Freely parameterizable pulse width modulated signal for PWM-capable output" must be parameterized for output to the PWM-capable output.

Example:

A PWM output with a frequency of 550.0 Hz is desired. The input signal has a value range of 0 to 2500. However, as from a value of 2400 a 100-% pulse width modulation should be issued.

The parameters of the signal generator are then as follows:

• Frequency_1 = (550.0 Hz) x 10 (owing to 0.1-Hz resolution) = 5500
• Maximum value = 2400

There is a PWM output with 2400 steps from 0 to 100%.