Siemens speed => pulses conversion

userxyz · Nov 22, 2007

I need a conversion from speed to pulses.

So the speed is 0 to 30 m/min.

The pulses: every 30 cm I need a pulse.

How can I calculate this ?

Should this be calculated in OB35 ?

manmeetvirdi · Nov 22, 2007

Combo
Why not use a encoder?
Its job is to provide pulses from the units travelled
Pulses will be arriving fast if movement is fast.
I think calulating the difference in number of pulses from previous scan of OB35 and present will give you the speed.

chud · Nov 22, 2007

Would also go for the pulse encoder. I think you will loose accuracy by doing a convertion from speed to pulses. Using the encoder will give you exact distance

PeterW · Nov 22, 2007

Number of options depending on your budget an accuracy required really.

1. Encoder and fast input card.

2. Proximity switch picking up from manufactured tooth-wheel fitted to non-driven shaft, direct to input.

3. As 2. above, except via a digital to analogue converter to give you 4-20mA into the PLC.

4. A timed pulse, calculated on the known speed, derived from the PLC. This one would be difficult if your varying the speed.

L D[AR2P#0.0] · Nov 22, 2007

Is this what you are after:

Code:

FUNCTION_BLOCK FB 1
TITLE =
VERSION : 0.1

VAR_INPUT
  OB35_EXEC_TIME : INT ; 
  rSpeedInMetresPerMIn : REAL ; 
  rDistanceBetweenPulsescm : REAL ; 
END_VAR
VAR_IN_OUT
  bPulseQ : BOOL ; 
END_VAR
VAR
  rStoredPositioncm : REAL ; 
END_VAR
VAR_TEMP
  rDistanceIncrementcm : REAL ; 
END_VAR
BEGIN
NETWORK
TITLE =
	  L	 #rSpeedInMetresPerMIn; 
	  L	 1.000000e+002; 
	  *R	; 
	  L	 6.000000e+001; //convert to cm per sec
	  /R	; 
	  L	 #OB35_EXEC_TIME; 
	  ITD   ; 
	  DTR   ; 
	  *R	; 
	  L	 1.000000e+003; 
	  /R	; //increment in position this scan
	  L	 #rStoredPositioncm; 
	  +R	; 
	  T	 #rStoredPositioncm; //update sum
NETWORK
TITLE =
	  L	 #rStoredPositioncm; 
	  L	 #rDistanceBetweenPulsescm; 
	  >R	; //rStoredposition > pulse distance ?
	  JCN   Exit; //no then exit
	  -R	; //else save difference for next accumulation
	  T	 #rStoredPositioncm; 
	  AN	#bPulseQ; //and toggle the output bit
	  =	 #bPulseQ; 
Exit: SET   ; 
	  SAVE  ; 
END_FUNCTION_BLOCK

Example call from OB35:

Siemens speed => pulses conversion

userxyz

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manmeetvirdi

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chud

Member

PeterW

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L D[AR2P#0.0]

Lifetime Supporting Member

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