Calculating the Safety Response Time

Preconditions

Preconditions for calculating the safety response time of your safety-related application:

oCorrect values are defined for the relevant parameters of the Safety Logic Controller (see chapter Determining and Setting the Safety Response Time Parameters).

oParameter ManualConfiguration is set to No for the I/O modules. With this setting, the values defined for the Safety Logic Controller are also applied to the I/O modules.

oIf the ManualConfiguration parameter is set to Yes for the I/O modules: Make sure that correct values are defined for the relevant parameters of each module involved. Refer to the chapter Relevant Module Parameters for details.

General Information

The safety response time is the time between the arrival of the sensor signal on the safety-related input module and the output of the request signal for the defined safe state at the safety-related output module.

Based on the calculated safety response time, the safety equipment must be planned and installed. For example, the safety response time delivers the required minimum distance of a safety-related sensor (such as a light beam) from the zone of operation.

WARNING

UNINTENDED EQUIPMENT OPERATION

oPlace operator devices of the control system near the machine or in a place where you have full view of the machine.

oProtect operator commands against unauthorized access.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

The following figure illustrates the influences on the safety response time:

The safety response time (SRT) is calculated as follows:

SRT = processing time in the safety-related input module (see next section)

+ input transport time (bus transfer input module -> SLC)

+ application processing time in the SLC

+ output transport time (bus transfer SLC -> output module)

+ processing time in the safety-related output module (see next section)

As shown in the figure above, the total lag time of the entire system from the occurrence of the safety function requesting event until the machine/plant is in the defined safe-state, also comprises the signal processing time of the safety-related sensor as well as the time for the actuator to stop.

For further and detailed background information, also refer to the chapter <Font uline="N" o="N" fa="Oblique" fw="Regular">Safety Response Time</Font> of the EcoStruxure Machine Expert - Safety - User Guide.

Processing Times in I/O Modules

For safety-related Schneider Electric I/O modules, the following signal processing times must be considered.

Schneider Electric input modules:

oConfigured filter value of the switch-off filter

o5000 µs when configuring the external clock signals

oI/O update time for TM5SAI4AFS (analog current measurement) and TM5STI4ATCFS (analog temperature measurement)

oModule processing time (timebase + I/O update time) for counter (TM5SDC1FS) module

NOTE: The I/O update time value depends on the configured input filter parameter. The module processing time depends on the configured timebase.

Schneider Electric output modules:

oTM5SDOxxxx modules: 800 µs max.

oTM5SDM4DTRFS: 50 ms max. (integrated relay)

oTM7SDM12DTFS: 1 ms max.

Calculating the Safety Response Time

Step	Action
1	Select Project > Response Time Calculator Result: The Result section at the bottom shows the overall worst case response time for the user-defined functional safety system.
2	You can now calculate the safety response time for individual input-output signal paths as follows: Select the input module for which the response time is to be calculated, and, if applicable, an input channel of this module. Result: The response time relevant parameters set for the selected input module/channel are shown in the area below. While no module is selected, the parameter values are zero.
3	In the right list, select the output Module for which the response time is to be calculated. Result: The dialog automatically shows the calculated response times for the selected path. Document these values for verification purposes. Observe the hazard message below this table.

Step

Action

Select Project > Response Time Calculator

Result: The Result section at the bottom shows the overall worst case response time for the user-defined functional safety system.

You can now calculate the safety response time for individual input-output signal paths as follows: Select the input module for which the response time is to be calculated, and, if applicable, an input channel of this module.

Result: The response time relevant parameters set for the selected input module/channel are shown in the area below. While no module is selected, the parameter values are zero.

In the right list, select the output Module for which the response time is to be calculated.

Result: The dialog automatically shows the calculated response times for the selected path. Document these values for verification purposes.

Observe the hazard message below this table.

WARNING

UNINTENDED EQUIPMENT OPERATION

oVerify that the signal processing time within the sensor is included in the overall safety response time calculations.

oVerify that the time required by the actuator to come to a standstill is included in the overall safety response time calculations.

oValidate the total lag-time of the system and thoroughly test the application controlling for lag-time.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

NOTE: During commissioning and operation of the system, the safety response time has to be optimized, if required.