PSM Arithmetic, Example Of PSM Function - GF54.21-D-3055-01TSK

Model 447, 448 

with code ED5 (Parameterisable special module) 

with code XM7 (MOPF II) 

Engine speed, characteristic block 

Model 907, 910 

with code ED5 (Parameterisable special module) 

with code XJ4 (Modification year G4-I) 

Engine speed, characteristic block 

Courtesy of MERCEDES-BENZ USA

Engine speed function blocks 

The engine speed (interior CAN (CAN B): "EngRPM") can be output at one of the pulse-width-modulation-compatible outputs as a pulse-pause modulated signal with T = 400 μs.

Formula: Pulse [1/s] = Constants factor * Engine speed [rpm]/Motordrehzahl [160

From a pulse frequency of 1, 250 pulses/s, the cycle duration of the pulse-width-modulated signal is so small that a duty cycle of 50% is reached with a pulse length of 400 μs. In order to meet the requirement for a 400 μs pulse length, the duty cycle increases at higher pulse frequencies. If the cycle duration reaches the pulse duration of 400 μs, switch-on takes place without pulse width modulation (PWM) (e.g. K = 10 and rpm ≥ 15, 000). 15.000

The engine speed function is specified through the programmable logic control (PLC) group, arithmetic unit and the multifunction output (MFA) blocks. The picture shows the simplified function block operation. The configuration is available in the tables.

Function description of implementation 

Comparator 4, calculation step 1 (Comp 4): 

• Limit valid value range of input signal to 0 to 16 392 rpm; 0 is output for values over 16, 392 rpm.

Arithmetic block 6, calculation step 2 (Calc 6): 

• Multiply input signal by constant factor (constant 9). Here, the upper limit value ("k*16, 392") must be recalculated and configured.

Arithmetic block 7, calculation step 3 (Calc 7): 

• Conversion to cycle duration.

Comparator 5, calculation step 4 (Comp 5): 

• Limitation of maximum cycle duration

  (Constants 12 →15, 000 =Konstante 12 15.000 400 rpm). For smaller values, the pulse duration (Constants 11) is output, otherwise 0. Konstante 11 sonst 0.

Multifunction output block (MFA 9): 

• Outputs the PWM at the output.