Positive and Negative edge detection

naturephoenix · Apr 9, 2015

How to make in STL(S7-300) potivite or negative bridge.
I want to start pump only on positive edge of the bit
"start_pump"

balash · Apr 9, 2015

EU = edge up
ED = edge down

ex.

Code:

L "btn_start"
[B]EU[/B]
S "start_pump", 1

Manglemender · Apr 9, 2015

Code:

A   Start_Pump_Req
FP  Start_Pump_Mem
=   Start_Pump_Edge

The Start_Pump_Mem bit needs to be a persistant memory (Marker or Data Block bit) type rather than a "temp" and then Start_Pump_Edge will be true on the rising edge of Start_Pump_Req for one processor scan only.

Substitute FN for a falling edge.

Nick

Jeebs · Apr 9, 2015

In STL, you use FP (pos edge) and FN (neg edge).

balash · Apr 9, 2015

Jeebs said:
In STL, you use FP (pos edge) and FN (neg edge).

Yes, Yes, EU and ED is from Microwin (S7-200 series)

naturephoenix · Apr 10, 2015

Manglemender said:
Code:

A Start_Pump_Req FP Start_Pump_Mem = Start_Pump_Edge

The Start_Pump_Mem bit needs to be a persistant memory (Marker or Data Block bit) type rather than a "temp" and then Start_Pump_Edge will be true on the rising edge of Start_Pump_Req for one processor scan only.

Substitute FN for a falling edge.

Nick

Ty

Manglemender · Apr 10, 2015

Interestingly, you can achieve the same functionality without the FP instruction as follows:

Code:

A   Start_Pump_Req
AN Start_Pump_Mem
=   Start_Pump_Edge

A   Start_Pump_Req
=  Start_Pump_Mem

This works because the the program is executed sequentially and demonstrates why the memory bit must retain its condition from one one scan to the next. This can be done in ladder too but requires 2 networks. There are ladder equivalents of FP and FN available too.

Nick

Lare · Apr 11, 2015

Manglemender said:
Interestingly, you can achieve the same functionality without the FP instruction as follows:

Code:

A Start_Pump_Req AN Start_Pump_Mem = Start_Pump_Edge A Start_Pump_Req = Start_Pump_Mem

This works because the the program is executed sequentially and demonstrates why the memory bit must retain its condition from one one scan to the next. This can be done in ladder too but requires 2 networks. There are ladder equivalents of FP and FN available too.

Nick

one network solution:





 req               mem       edge

-| |---------------|/|--------( )

               |

               |             mem

               ---------------( )

For falling edge negate reg

Positive and Negative edge detection

naturephoenix

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balash

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Manglemender

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Jeebs

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balash

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naturephoenix

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Manglemender

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Lare

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