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

Model 907 

with code ED5 (Parameterisable special module) 

Engine speed, characteristic block 

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 us.

Formula: Pulses [1/s] = constant factor * engine speed [RPM]/60

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 takes place without pulse width modulation (PWM) (e.g. K = 10 and RPM ≥ 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; for values over 16 392 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*16 392") must be recalculated and configured.

Calculation block 7 calculation step 3 (Calc 7): 

• Conversion to cycle duration.

Comparator 5, calculation step 4 (Comp 5): 

• Limitation of maximum cycle duration (constant 12 → 15 000 = 400 RPM). At smaller values, the pulse duration (constant 11) is output, otherwise 0.

Multifunction output 6 block (MFA 6): 

• Outputs the PWM at the output.