Adjustable parameters

Duty Cycle

The duty cycle can be set individually for each channel to a value between 0 and 100 %. The value is set per channel via the output process data PWM Outputs Channel n → PWM Output. The maximum possible value in the process data is 32767.

• Duty Cycle 0 % = 0
• Duty Cycle 50 % = 16384
• Duty Cycle 100 % = 32767

The current value for the output can be read out for diagnostic purposes in the CoE object 0x60n0:13 Output duty cycle. Alternatively, the objects 0x1A01, 0x1A03, 0x1A05 and 0x1A07 can also be mapped in the process data. Here the current process data value can then be read cyclically via the Output duty cycle variable.

Master Gain

The Master Gain sets the total brightness across all channels and is therefore only adjustable once for all four channels to dim all channels by the same factor. This value must be set in the process data. For this purpose the object 0x1604 PWM Outputs Device must be mapped in the process data in Sync Manager 2 Outputs or alternatively the Predefined PDO Assignment 4 Ch + Master gain must be selected. In addition, the value for the Master Gain can be permanently specified via the CoE object 0xF819:12 as long as the object is not mapped in the process data. The brightness can be set between 0 and 100%.

If the value is mapped into the process data, it is initially 0 by default. This value must be changed to the desired Master Gain value > 0 in order to see a light at the output of the EJ2564 EtherCAT plug-in module. The maximum possible value is 32767. The actual output value of the duty cycle is then calculated via the value entered in the process data for the duty cycle multiplied by the factor (Master Gain/32767).

If Master Gain and the gamma value are used together to scale the output, the output value is always calculated first with the Master Gain and then with the gamma.

PWM frequency

The frequency of the PWM output for all channels can be changed in CoE object 0xF819:11 PWM frequency. The value is specified in Hz. The default value is 5000 Hz. The frequency can be set between 1 and 16000 Hz via this object.

Depending on the set frequency, the number of steps changes from the lowest to the highest brightness. With increasing PWM frequency the resolution decreases. The resolution or step size is displayed in the CoE object 0xF919:11 Resolution.

In the delivery state with a PWM frequency of the brightness is changed approx. every five PDO increments. (32767/6399 = 5.12)

At the low frequencies, where a visible flashing is generated, it must be considered that the individual pulses have the maximum brightness and cannot be dimmed, since dimming is usually realized at fast frequencies via the duty cycle. This means that at low frequencies no arbitrary color mixing is possible. If flashing with any color mixture is desired, it must be implemented in the PLC program.

Ramp Time

The Ramp Time specifies the time for dimming up/down from the lowest to the maximum brightness. The time can be set for each channel individually in the CoE object 0x80n0:25 Ramp time. For values smaller than 0.05 s the ramp is inactive and the output value is controlled synchronously with the cycle. The maximum time for the ramp time is 10000 s.

Gamma - scaling of the output

The gamma value can be used to adjust the scaling of the output. The brightness behavior can, for example, be approximated to the perception of the human eye. Gamma can be set per channel in the CoE object 0x80n00:24 Gamma. If this value is set to 1.0, the scaling is linear. Some progressions of the output at different gamma values can be taken from the following figure.

The output is calculated using the following relationship: (Current_process_data_value/Maximum_process_data_value)^Gamma

The following is an example calculation for the process data value 4096 and Gamma 0.5:

(4096/32767)^0.5 = 0.35

The result is therefore 35%. The actual output value of the duty cycle corresponds to the specified value from the process data when gamma is equal to 1.0.

If Master Gain and the gamma value are used together to scale the output, the output value is always calculated first with the Master Gain and then with the gamma.

Example application for the linearization of brightness for the human eye:
The brightness perceived by humans increases more steeply in dark areas and less steeply in bright areas. The human eye is assigned a gamma value of approx. 0.3 to 0.5. If you want to perceive the brightness signal of a display device (e.g. a monitor or an illumination device) linearly, you have to pre-distort it with the reciprocal of the gamma value (approx. 1/0.3 = 3.3 to 1/0.5 = 2) so that the two non-linearities cancel each other out and the course appears linear to the observer. For the gamma values of the EJ2564 EtherCAT plug-in module a value between 2 and 3.3 would have to be specified for the human eye.

Behavior in watchdog case

The behavior in the watchdog case can be specified for each channel in the CoE object 0x80n0:05 Watchdog. It can be selected whether the output keeps the last process data value in the watchdog case or whether it assumes a value specified in CoE object 0x80n0:0D Default output. This can be used for example for error indication, so that in the watchdog case all channels are switched off except the channel with the red LED to signal the error.

With the default output value from 0x80n0:0D it must be noted that this is the default duty cycle. 32767 therefore corresponds to the maximum brightness.

In the watchdog case, the values entered in the CoE for the frequency, gamma and master gain are retained. Specified ramp times have no influence.