Internet PLC Forum

Thierry,

You will have to test this.  I have tested most of the stepper motor hardware and firmware, but have not attempted to change the PPS (step rate) of a running stepper. 

I do use the PWM outputs to generate variable frequency pulses.  The PWM outputs will change frequency while running. I have verified this with a digital oscilloscope and see that the output goes to the new frequency very "cleanly".  You could use a PWM OUPTUT to control a stepper motor and change the frequency, periodically.

The following code has been extracted from one of my products that is in production.  The code is called every 0.1 second (10 Hz rate) and changes the PWM frequency.  The code is used to simulate the output of a flow meter. The physical flow meter outputs a variable frequency signal that is proportional to the flow of fluid through the flow meter.

if (VFDCurrentHz < 5.00)
   ' Main Pump speed is too low to generate meaningful flow values
   '
   SimProductGPM = 0.0
   SetPWM 1, 0, 1         ' 0% duty cycle so output is "OFF"
else
   ' The main pump is running so we will calculate flows based on VFD frequency
   '
   SimProductGPM    = 0.0007 * VFDCurrentHz * VFDCurrentHz + 0.0194 * VFDCurrentHz + 0.7229

   ' Generate pulse output for flow.
   '
   SetPWM 1, 5000, SimProductGPM / 60.0 * ProductPPG
endif


Best regards,

Gary Dickinson

This is the PDF version of the documentation.

I am presenting the code that I have been using for the last 5 years as an alternative to the TBASIC ReadModbus, ReadMB2, WriteModbus and WriteMB2.

This code is supports all possible Modbus function codes.

This code is non-blocking. The PLC does not lock up waiting for a response from the slave device.

This code is an example of a user written communication protocol

This code allows you to see both the Modbus response packet and every byte received from the Modbus slave.  This allows you tremendous debug capability that is not available with the TBASIC Modbus support.

I will post the PLC code and the documentation in pieces to keep them under 200KB

Regards

Gary Dickinson

Dave,

I have been working with TRI's PLCs for over 15 years.  Their products have evolved and they have added significant new hardware and software features.  However their current documentation tends to be re-edits 20+ years old info.  

The 1..10Kz measurement system limits dates back to the generation of hardware that was new in about 2001.  The measurement system buried in the ASIC used for the Tile/Fx based PLCs is hardware based and uses a 10 MHz time base.  If your use the PulsePeriod() function the hardware zeros out a 32-bit hardware register on the rising edge of your input signal and then increments the register every 1 or 0.1 us until the next rising edge of your signal.  PulsePeriod returns the accumulated count.  I know this stuff because I broke the firmware in these PLCs and worked with their designers to fix it.

I suggest that you write tiny test PLC programs to figure out the details.  I'd estimate that 80% of my PLC programming is test code.

I, also, suggest that you call/email TRI's customer support.  They actually know the details of their products and have been very helpful.  

You are always welcome to pick my brain on this stuff.  My email address is in my user profile.

Gary d

Mark the number of steps before the stepper quits moving is about 2 billion.

If the step rate was 800 pulse/sec with the maximum step count your fan would run for about 31 days before it stops.

What is the expected max time that the fan needs to run? 1 day, 1 week or one month?  2 billion steps will handle it.

If your max run time is measured in minutes or hours, just program it for the max step count of &h7ffffff every time you run the fan.

If you are looking for variable speed to meet your air flow requirements, then the use of steppers system is not ideal.  I think that you will have to abort the current stepmove command and physically stop the stepper before changing the speed. This may be audibly annoying.

Gary D

Neal,

I am glad that you were able to get the PLC firmware sorted out for your client.

Please feel free to contact me if you have questions with how to get the most out of these PLCs.  My email address is in my profile on the forum.

Thanks,

Gary D*ckinson

Integer math and operator precedence is the answer to your perplexity.

9 divided by 5 is 1 with integer math.

Your spreadsheet and your calculator are doing floating point math. 9 divided by 5 is 1.8 with floating point math.  That is why the results are different then when you use a spreadsheet or a calculator.

Operator precedence.  The parenthesis in your expression:

     F = (C * (9/5)) +32

Forces TBASIC to perform the 9/5 division first.  Remember that 9/5 is 1.  The next thing TBASIC does is multiply the value of C by 1. Then TBASIC adds 32 and finally will assign the results of the arithmetic expression to the variable F.

I do not know how smart TBASIC's expression parser is.  If it was really smart it would, at compile time, precompute that the division of the constant subexpression 9/5 to be 1 and not actually do a division at run time. If may, also, recognize that the multiplication of the variable C by 1 is always the value of C.  TBASIC could simplify your expression to this because this is exactly what you wrote:

  F = C +32
Rule #1 for integer math is to do all your additions and multiplications first.  Do your division last to preserve accuracy.

You might want to rethink how you are converting an ADC value to temperature in F.  if you need F go from ADC units directly to F.

I would used scaled integer values.

I would, also, oversample the ADC so that I are working with a 14 bit ADC value rather than the advertised 12 bit value.

Gary D*ckinson

I see this with Microsoft Edge, 32-bit Internet Explorer and Firefox on Windows 10.  The problem also shows up with Safari on iPads and iPhones. The fact that the Unicode characters show up on very different operating systems computer hardware is very interesting.

These are a few threads that shows funny characters:

http://www.triplc.com/yabbse/index.php?board=1;action=display;threadid=2367

http://www.triplc.com/yabbse/index.php?board=1;action=display;threadid=2314

http://www.triplc.com/yabbse/index.php?board=1;action=display;threadid=2276

http://www.triplc.com/yabbse/index.php?board=1;action=display;threadid=2227

The bit of the thread that shows them has been copied from the I-TRILOGi CF editor and pasted into a reply. Some of these characters, also came from a copy/paste operation from an simple text editor.

Most of the goofy characters are where ASCII tab characters were in the original source. It is not possible to input ASCII tab characters using a keyboard as YaBBSE ignores them, but it is possible using a copy/paste operation.

The odd Unicode characters did not show up when the replys were posted. Only recently have the odd characters appeared.  They did appear in my very recent posts, but I went back and replaced them with ASCII spaces to make the posts a bit less annoying.

Gary d