Functional description

This topic contains the following sections:

The safety-related SF_TwoHandControlTypeIII function block evaluates the switching behavior of a type 3 two-hand control device connected to the Safety PLC.
This involves evaluating the switching states of both the buttons on the two-hand control device. The S_TwoHandOut output only becomes SAFETRUE if both inputs switch from SAFEFALSE to SAFETRUE within 500 ms, either simultaneously or consecutively (if both buttons on the two-hand control device are pressed after being not actuated before).
If there is an interval > 500 ms between the switching operations of the button (SAFEFALSE -> SAFETRUE), the function block detects this as an error (the Error output becomes TRUE and S_TwoHandOut = SAFEFALSE).

Note
Unlike the type 3 two-hand control device described here, evaluation by the type 2 version takes place without consideration of a specific duration within which both buttons must be actuated.

As soon as one of the inputs is no longer SAFETRUE, the S_TwoHandOut output switches to SAFEFALSE. The output can only switch to SAFETRUE again once both inputs are showing the SAFEFALSE state. S_TwoHandOut also becomes SAFEFALSE if the function block has detected an error.

The function block executes stop category 0 at its output.

SAFETRUE signal at one input during function block activation

While function block activation is taking place (with input Activate = TRUE), both inputs must show the SAFEFALSE state. This means that none of the buttons on the two-hand control device must be actuated. Otherwise, the function block detects this as an error (output Error = TRUE, and consequently S_TwoHandOut = SAFEFALSE).

Two-hand control device with two-channel buttons

Irrespective of whether there is a single-channel or two-channel connection between the buttons of the two-hand control device and the Safety PLC, both inputs S_Button1 und S_Button2 are only connected to one signal each. When using two-channel buttons, each two-channel signal must be evaluated or monitored as follows:

Either through a suitable upstream safety-related function block, e.g., SF_Equivalent, if the button has two N/C contacts.
Or the evaluation of equivalence or antivalence must be performed in the safety-related input device, also see section "Application example".

Note
Depending on the result of the risk analysis you have performed, you will have to implement cross-circuit detection. When doing so, take into account the relevant information in the online help and in the User Manual for the Safety PLC.