Greetings all,

I'm attempting to duplicate the function of a PMul instruction from the Studio 5000 platform from Rockwell Automation and am not getting the exact results I had hoped. I was looking for something similar in a motion technology object but am not certain about their full list of uses.

In AB PLC's the scan times can run very long, mostly due to the memory layouts and programming methods. The PMul will read a high speed input or encoder and measure the difference between scans of the pulse count then take the remainder and add if to the count for use later in the scan for tracking purposes.

Does anyone have any ideas on either which technology object or motion instruction could be used, or the best method to write this in SCL?

Thanks!!

hess1975

In AB PLC's the scan times can run very long, mostly due to the memory layouts and programming methods.

OT: <sarcasm> There must have been a reason I'd dropped using AB years ago...</sarcasm>

Not knowing what you want to do with it, I'd suggest using or a high speed counter TO  or an external encoder TO. Note that both of them need special hardware.

I've completed many Rockwell to Siemens conversions, and the Pulse Multiplier was a fun one to tackle. Fortunately for me I had some help from some old Reliance Electric guys that knew the background math for the PMul instruction.

Instruction below and FB attached.

Variables;

"Input"
Multiplier  -  Real
"Output"
Out  -  Real
Actual Pos  -  UDInt
"InOut"
In  -  UDInt
Static
Scan CTU  -  UDInt
Real accum  -  Array[0..9] of Real
Remainder -   Real
Temp -   Real
Temp Out  -  Real
Scan Differential  -  Real

SCL;

#"Real accum"[#"Scan CTU"] := UDINT_TO_REAL(#In);

IF #"Real accum"[0] > #"Real accum"[1] THEN
#"Real accum"[2] := #"Real accum"[1];
#"Real accum"[3] := #"Real accum"[0];
ELSIF #"Real accum"[0] < #"Real accum"[1] THEN
#"Real accum"[2] := #"Real accum"[0];
#"Real accum"[3] := #"Real accum"[1];
END_IF;

#"Scan Differential" := #"Real accum"[3] - #"Real accum"[2];

#Temp := ((#"Scan Differential"*#Multiplier) + #Remainder);

#"Temp Out" := #Temp / 100000;

#Remainder := #Temp - (#"Temp Out" * 100000);

#Out := #"Temp Out";

#"Scan CTU" := #"Scan CTU" + 1;

IF #"Scan CTU" > 1 THEN
#"Scan CTU" := 0;
END_IF;

#"Actual Pos" := #In + REAL_TO_UDINT(#"Scan Differential");

Hello,

Generally your calculation about PMul block is fine, but one very important part of PMul block is missing protection against "rollover". In simple example if you will have encoder 12-bits and this we know it will work from -2048 ... 2047 (4095 - 12bits), if yor encoder make roll over from It=2040 to It+1=-2040 the difference will be -2040 - 2040 = -8080, and scan before it would have It-1=1940 and It=2040, one scan before difference 2040-1940=100, I think you should also check and look your difference and word size of HSC register...

The point is you will accumulate the pulses in the register which have the end. the problem will start when you will come to rollover of the register where you accumulate the pulses. The function which is written will work but ones per register rollover will fail.

you need to implement the modulo caluclation to avoid rollover...