PSM Arithmetic, Example Of PSM Function - GF54.21-S-3055-01TRE

Model 447 

With Code ED5 (Parameterisable special module) 

Except Code XM7 (MOPF II) 

Engine speed, characteristic block 

Model 448 

With Code ED5 (Parameterisable special module) 

Except Code XM7 (MOPF II) 

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 where T = 400 μs.

Formula: Pulse [1/s]= constant factor *engine speed [rpm]/ [160

As of a pulse frequency of 1250 pulses/s, the cycle duration of the pulse width modulated signal becomes so short that a duty cycle of 50 % is achieved 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 is performed without pulse width modulation (PWM) (e.g. K = 10 and rotational speed ≥ 15 15000).

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 16392 rpm; for values over 16392 rpm, 0 is output.

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

• Multiply input signal by constant factor (constant 9). Here, the upper limit value ("k*16392") must be recalculated and configured.

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

• Conversion to cycle duration.

Comparator 5, calculation step 4 (Comp 5): 

• Limit the maximum cycle duration (Konstante 12 15 →15000 = 400/min). In the case of lower values, the pulse duration (Konstante 11) is output, otherwise 0. sonst 0.

Multifunction output 6 block (MFA 6): 

• Outputs the PWM at the output.