Application Example: Two-Hand Control

A two-hand control (Category 4, PL e) is used as a programming example of CODESYS Safety for EtherCAT Safety Module and illustrated as an FBD implementation.

The two-hand pushbuttons each consist of a combination of normally closed and normally open contacts on the safe inputs of an input module (example: EL1904). Testing of the inputs is active and the signals are also checked for discrepancy (200 ms). In addition, the synchronous actuation of the two pushbuttons is activated with a monitoring time of 500 ms.

The feedback loop is read in via a safe input. The contactors K1 and K2 are connected in parallel to the safe output. The measurement of current and testing of the output are active for this circuit.

Figure 21. Layout of the two-hand control with EDM

Figure 22. Implementation of the programming example: Two-hand control with EDM

Table 1. Inputs

Name	Data Type	Description
`S1_1`	`SAFEBOOL`	Two-hand pushbutton 1: NO (normally open)
`S1_2`	`SAFEBOOL`	Two-hand pushbutton 1: NC (normally closed)
`S2_1`	`SAFEBOOL`	Two-hand pushbutton 2: NO (normally open)
`S2_2`	`SAFEBOOL`	Two-hand pushbutton 2: NC (normally closed)
`I_K1_K2`	`SAFEBOOL`	Contacts of `K1` and `K2` for reading back

Table 2. Outputs

Name	Data Type	Description
`O_K1_K2`	`SAFEBOOL`	Actuation of contactors `K1` and `K2`
`bError`	`BOOL`	Error flag of `FB_TWOHAND_1`
`bError`	`BOOL`	Error flag of `FB_EDM2`

Table 3. Function block parameters

Function Block	Input	Constant Value	Description
`FB_TWOHAND_1`	`tDiscTime12`	`T#200ms`	Discrepancy time between NC contact and NO contact of `S1`
`FB_TWOHAND_1`	`tDiscTime34`	`T#200ms`	Discrepancy time between NC contact and NO contact of `S2`
`FB_TWOHAND_1`	`tDiscTime`	`T#500ms`	Discrepancy time between `S1` and `S2`
`FB_EDM2`	`tSwitchOnMonitoring`	`T#500ms`	Switch-on delay
`FB_EDM2`	`tSwitchOffMonitoring`	`T#500ms`	Switch-off delay