Pwm Function Block

The Pwm function provides a fixed cycle time with a variable duty cycle time. When the pulse width equals the cycle time, the duty cycle is 100 %, and the output is turned on continuously.

Figure 1:Pwm - Function Block

Figure 2:Pwm - Property Sheet

If parameter Zero Time = 0 % and parameter Full Time = 100 % and input In = 0 %, then Pwm period interval is stop and restart with the 0 % (Off).

Note: Restarting means that input In value > 0 % can switch On after the Pwm Period is expired. This enables fast switch-off (Fire, Drip Pan, Condensation) for safety reasons.

Special case, if Zero Time = 0 % and Full Time = 100 %: As soon as In = 0 %, the Pwm period interval is stopped and restarted with the 0 % (Off). Restarting means that a value > 0 % can switch ON after an expired Pwm Period. This enables fast switch-off (Fire, Drip Pan, Condensation) for safety reasons.

Inputs

Input Name

Description

Enable

This is a safety feature to switch a running Pwm output immediately to off. If Enable set to "true" "1", then the Pwm cycle is started. For Reverse operation, the output is on in case of Enable set to "false" "0".

In

This input slot is typically connected to the PID output. For a cooling and heating control, a NumericSelect FB must be used between the PID and this output FB, which then only transmits the cooling or heating PID output value to this output FB.

Manual

The input is used for manual override of the "In" input of the PID controller (automatic). Under certain conditions.

Interlock

Interlock is used, if the output may open only if a fan is running or an airflow contact says flow. The output remains OFF until interlock is "true". Even if Manual Override > 0%, the output keeps closed until interlock is "true" "0". The output Out Pwm is switched off immediately. The Pwm cycle is terminated immediately. 1 or 0, Out Pwm is controlled as per the input value.

Self Test Cycle

It is a time after the output toggles between 0% and 100%. Whenever the time has elapsed, the output toggles. "0" or "null" disables the self test.

Start Exercising

It prevents the valve becoming stuck due to deposits in the water when the valve is closed for a longer period.

Table 1:Inputs of Pwm Function

Outputs

Output Name

Description

Out Virtual Position

The output shows the current position of the Pwm output as result from all input conditions.

Out Pwm

This output must be connected to the physical output like a relay or a triac.

Out Self Test Running

The output is true, if the self-test is running

Out Cause

The output serves to understand what the function block is currently doing.

Disabled =16, Manual =32, Interlock false =64, Self Test active =128, Exercising active =256, OperationIsOff =512.

Table 2:Outputs of Pwm Function

Parameter

Parameter Name

Description

Operation

Type the value to operate the actuator in direct or reverse action.

Off =1, Direct =1, Reverse =2

Pwm period

Type the pulse width period in seconds. The Pwm period is the time divided into between 0 and 100%. If the Pwm period is e.g. 100 sec and In = 30%, the output would be ON for 30 sec and then OFF for 70 sec. Then the cycle is repeated, ON for 30 sec and OFF for 70 sec.

Zero Time

Type the Zero Time value in percentage. When 0% command is given, output Out Pwm will be set to 1 for the time duration specified in this parameter.

Full Time

Type the FullTime value in percentage. When 100% command is given, output Out Pwm will be set to 1 for the time duration specified in this parameter.

Weekly Exercising

If the actuator is not moving for more than 1 week, exercise will be performed.

Disable =0, Enable =1

Out Save

Master Sync Enabled: If you set it to "true" the last output will be set as output for one cycle after the controller restarts. The application can use it to return to the same state before the controller restart.

Out Virtual Pos: To enable or disable the Out Virtual Pos feature.

Out Pwm: To enable or disable the Out Pwm feature.

Out Self Test Running: To enable or disable the Out Self Test Running feature.

Out Cause: To enable or disable the Out Cause feature.

Table 3:Parameters of Pwm Function

Examples

The below diagram explains the Pwm output behavior.

Example 1

1.       Operation = Direct

2.       Pwm period = 100 Sec

3.       Zero Time = 0%

4.       Full Time = 100%

Figure 4: Pwm output behavior.

Example 2

1.       Operation = Direct

2.       Zero Time Par = 50%

3.       Full Time Par= 100%

4.       In = 50%

Figure 5: Pwm output behavior.

Example 3

1.       Operation = Direct

2.       Zero Time Par = 25%

3.       Full Time Par = 100%

4.       In = 20%

Figure 6: Pwm output behavior.

Refer to General Description for general information about IRMN4 Function Blocks.