Record Filtered Position Values / RTI PLC Run Time

[sdefisher]

I am running a real time PLC that is stuffing position data into registers that I can read from later. I'd like to filter the positions to take random out . My plan was to make a simple average. Is there a feature in PowerPMAC that can already do this for me, or do I need to roll my own? How fast is the RTI PLC operating (or how can I look it up on my machine?). I am reading the data around 2000 Hz, so I need to make sure my running average is a lot faster than that. 

[Eric Hotchkiss]

5 hours ago, sdefisher said:

I am running a real time PLC that is stuffing position data into registers that I can read from later. I'd like to filter the positions to take random out . My plan was to make a simple average. Is there a feature in PowerPMAC that can already do this for me, or do I need to roll my own?

You can set an encoder conversion table entry to act as a digital tracking filter by changing the values of index1 and index2. A "motor" could then be set up to read the position and display it in the position window. It would probably look like below.

EncTable[n].type = 1 // Single register read
EncTable[n].pEnc = [HardwareLocation].a
EncTable[n].index1 = (filter Ki) // For possible digital tracking filter
EncTable[n].index2 = (filter gain) // For possible digital tracking filter
EncTable[n].ScaleFactor = 1/65536 // For result units of LSBs
Motor[x].pEnc = EncTable[n].a // Use result for position-loop feedback
Motor[x].pEnc2 = EncTable[n].a // Use result for velocity-loop feedback

You could also write your own code in PLC 0 (the RTI PLC) if you feel setting up a motor to read the position is too complicated.

5 hours ago, sdefisher said:

How fast is the RTI PLC operating (or how can I look it up on my machine?). I am reading the data around 2000 Hz, so I need to make sure my running average is a lot faster than that. 

RTI is divided down from Servo based on Sys.RtIntPeriod.

[sdefisher]

16 hours ago, Eric Hotchkiss said:

You can set an encoder conversion table entry to act as a digital tracking filter by changing the values of index1 and index2. A "motor" could then be set up to read the position and display it in the position window. It would probably look like below.

EncTable[n].type = 1 // Single register read
EncTable[n].pEnc = [HardwareLocation].a
EncTable[n].index1 = (filter Ki) // For possible digital tracking filter
EncTable[n].index2 = (filter gain) // For possible digital tracking filter
EncTable[n].ScaleFactor = 1/65536 // For result units of LSBs
Motor[x].pEnc = EncTable[n].a // Use result for position-loop feedback
Motor[x].pEnc2 = EncTable[n].a // Use result for velocity-loop feedback

Any possibility of self referencing a previous EncTable Entry? 

e,g, EncTable[11].pEnc = EncTable[3].a

[Eric Hotchkiss]

Take a look at EncTable[n].PrevEnc. The name might be a little confusing, it's where the ECT output value is saved.
EncTable[11].pEnc=EncTable[3].PrevEnc.a

Because PrevEnc is an integer, this means a type 1 ECT entry (integer read) can still be used.

Note that this register must be multiplied by EncTable[n].ScaleFactor to get the result you expect. This means you can set EncTable[11].ScaleFactor=EncTable[3].ScaleFactor to read both Motor 11 and Motor 3 positions at the same scale.

I tried this with a digital tracking filter on my quadrature encoder and I needed EncTable[11].ScaleFactor = EncTable[3].ScaleFactor = 1/256 to read the filtered value correctly.

Also note there is a section in the Power Brick ARM Manuals titled "Digital Tracking Filter" that calculates EncTable[n].index1, EncTable[n].index2, and EncTable[n].index4.
https://assets.omron.com/m/661730249d3863b4/original/Power-Brick-LV-ARM-User-Manual.pdf

EncTable[11].type = 1
EncTable[11].pEnc = EncTable[3].PrevEnc.a
EncTable[11].index1 = // From Brick PLC
EncTable[11].index2 = // From Brick PLC
EncTable[11].index4 = // From Brick PLC
EncTable[11].ScaleFactor = EncTable[3].ScaleFactor // or maybe 1/65536
Motor[x].pEnc = EncTable[n].a
Motor[x].pEnc2 = EncTable[n].a