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

Model 907 

with code ED5 (Parameterisable special module) 

Outside temperature, arithmetic block 

Function blocks for outside temperature 

The outside temperature (interior CAN (CAN B): "AirTemp_OutSd") can be output on one of the pulse-width-modulation-compatible outputs (A).

Formula: duty cycle = (outside temperature [°C] + 40 [°C])/125 [°C]

If a value (W) outside the valid range is sent, the last valid value (W) is used. If a valid value (W) is still not available, 0 % pulse width modulation (PWM) is output. The PWM function for the outside temperature is implemented using groups of the programmable logic controller (PLC), arithmetic unit and multifunction output blocks. The picture above shows the simplified linking of the function blocks. The configuration is available in the tables.

Function description of implementation 

Comparator 6, calculation step 1 (Comp 6): 

• Check that the input signal is in the valid value range (0 to 250), then output "1", otherwise "0"

Comparator 7, calculation step 2 (Comp 7): 

• Restrict the valid value range of the input signal to 0 to 250; 250 is output for values (W) over 250.

Arithmetic unit memory (Memory 1): 

• Output the received signal if it is in the valid value range, otherwise output the value (W) stored last.

Flip-flop 2 (FF2 PLC G12): 

• Output "1" if a valid signal was received after wake-up of a control unit.

Value table 1 (WT1): 

• If a valid signal has been received, the result is output by the memory, otherwise the default value ("0").

Calculation block 10, calculation step 4 (Calc 10): 

• Conversion of the valid signal from 0 to 250 to the value range 0 to 10 000 (0 to 100 %).

Multifunction output block (MFA 6): 

• Output of PWM: Frequency comes from constant = 2000 (200 Hz); capacity utilization is result of calculation block 10, calculation step 4 (Calc 10), output (A) is permanently ON, i.e. PWM is output by locally active control unit.

Signal identification number = Signal ID. The signal IDs are notated in hexadecimal form.