MLG-2 Height measurement using BBH (Blocked Beams Hold)

A very common application using MLG and MLG-2 is the height measurement.

But only a few know about the integrated functionality of "BBH". Thus only few are using it. But it's quite efficient to do it.
See why!

In those examples the maximum height of the object is not trivial to measure since the object is not symmetrical.
The beam status or pre-calculated values like "Last Beam Blocked" (LBB) always give you the current status. So in the example the detected height (LBB) or the beam status differ completely between situation 1, 2, 3 and 4.

That means the whole object has to pass the light curtain before the result of the final height is available.

So the following control unit (probably a PLC) would need to trace the whole data until the object is passed. A big effort...

Using BBH of the MLG-2 it's easy. As soon as BBH is activated all beams which are blocked during this period of time are hold. You can also define that the basic functions (like LBB) are calculated on basis of the hold beam status.
The resulting LBB values would look like this:

All what needs to be done is the activation and deactivation of BHH. This could be done in two ways:

• External input (a simple photo switch mounted over the conveyor to detect the leading edge could trigger BHH)
• IO-Link (PLC could activated BHH on basis of the beam status or on a basic function)

Example configuration of an IO-Link MLG-2 to be used with BBH function:

1. Beam Hold functionallity needs to be selected

→ Choose value 1 here

2. Define which basic function should be calculated on basis of the (internally) hold beam status. Also define if the (output) beam status or RLC should be hold.

→ For the example choose Index 260 (LBB) to be true.
==> As you see here you can have a mix of basic functions which are calculated on basis of the hold beam status and of basic functions which are calculated on basis of the live beam status.

3. Activation and Deactivation of BHH is simply done by setting or resetting bit no. 5 in the control byte (IO-Link Output-Process-Data)