Internet PLC Forum

The following logic will detect when the 3 inputs have been stable for the minimum time determined by the SetValue of TIMER, InputChange.

I'd give this logic a try,

Gary D.




  Detect Input Change.  Have any of the inputs changed
  since the previous scan through the ladder logic?

   Input1  Latched1                            InputChange
-----||-----|\|--------+--------------------------(RLY)
                       |
   Input1  Latched1    |
-----|\|-----||--------+
                       |
   Input2  Latched2    |
-----||-----|\|--------+
                       |
   Input2  Latched2    |
-----|\|-----||--------+
                       |
   Input3  Latched3    |
-----||-----|\|--------+
                       |
   Input3  Latched3    |
-----|\|-----||--------+


  When Inputs have remained stable longer than the
  SetValue of the InputStable TIMER then InputStable will
  be TRUE.

   InputChange                                 InputStable
-----|\|------------------------------------------(TIM)


  Remember Input state for comparison on
  Next scan of logic.

   Input1                                        Latched1
-----||-------------------------------------------(RLY)

   Input2                                        Latched2
-----||-------------------------------------------(RLY)

   Input3                                        Latched3
-----||-------------------------------------------(RLY)

Your programming example has several problems:

• In your first line, RLY[1] should have been RELAY[1]
• You have two "IF" statements, but only 1 "ENDIF"
• You don't need line numbers (@10, @20, ...) on any line except the target of the GOTO statment.
• You don't need the GOTO statement at all.
• I suggest that you use the TESTIO(x) function to test the state of an input rather than the RELAY[1] mechanism because it is easier to read and to maintain.

The following code is a bit more straight forward and may be easier to debug/maintain:

IF TestIO(Input_X) OR ((DATE[4]<1 OR DATE[4}>5) AND (TIME[1]<=7 OR TIME[1]>=16))
   SetIO PWR_TV
   SetIO PWR_COMP
ELSE
   ClrIO PWR_TV
   ClrIO PWR_COMP
EDNDIF

Doug,

If your application cannot tolerate the +/- delay of the ladder logic scans, you should rethink your use of a PLC for this critical bit of timing.  

The only way you can reduce the variability is to do everything relaated to handing the external event and your time delay need in the interurpt handling function.  Start the timer, force the output, poll for timer to compled clear the output and then exit the custom funciton. This has the negative side effect of shutting dow the PLC for the duration of your delay.  The ladder logic scan mechanism will be suspended and the system will be unresponsive to changes on inputs.

You may want to figure out how to do the precise time delays using circuity external to the PLC.   I'd investigate the use of cheap microcontrollers such as Basic Stamp, Rabbit or PIC.  The PLC can handle the user interface and "talk" to the external microcontroller via the RS-485 serial port. The microcontroller could act as a precision, programable time delay relay.
 
Gary D

I've taken a stab at using the interrupt input mechanism to interface a low speed quadrature encoder at 2X to the M-series PLC.

This approach is just fast enough.  I connected the the A phase to Input pins 3 and 4 (Interrupts #1 and #2).  I connected the B phase to Input #5 (no special handling).  Variable A will be used to hold the current count. RELAY "TIC" will be used to comunicate to the ladder logic that the A variable has changed.

I initialized the interrupt system with the following TBASIC code:

INTRDEF 1, 2, 1      ' Positive Edge Interrupt handler
INTRDEF 2, 3, 0      ' Negative Edge Interrupt handler

A = 0            ' A will be used to store count

Interrupt #1 will handle the positive edge of phase A and the TBASIC code is as follows:

' PosEdgeA Interrupt handler
'
' Increment/Decrement based on phase B
'
if testIO(B) : A=A+1 : else A=A-1 endif
setIO TIC

Interrupt #2 handles the negative edge of the A phase:

' NegEdgeA
'
' Increment/Decrement based on phase B
'
if testIO(B): A=A-1 : else A=A+1 endif
SetIO TIC


Thanks for all you your support.  

Gary D

I have no problems with font size with the TRilog tools.

I'm using a wide-screen monitor with a native resolution of 1920x1200.  My system, now is Vista-32 and the most recent version of Java (1.6.0_15-b03).

I was using the same monitor with my XP system.

The default screen font size is determined by Windows.  There is a setting that controls the size and appearance of the default screen font.  I have set my screen resolution to 96 DPI.

For XP, right click on an empty space on the desk top.  From the pop up window select:

    Display Properties > Settings > Advanced > Display dpi

Change the DPI settings to something like 120 DPI for really big text.

For Vista, right click on an empty space on the desk top. From the pop up window select:

    Personalize > Adjust font size (DPI) > Custom DPI ...


gary d

I attempted to interface a mechanical rotary encoder to a T100MD+ PLC.  The goal was to use the encoder for a simple input control for PLC based project.  Just one knob and one or two external push button switches.

These encoders are typically used as volume controls on car radios and many other consumer devices.  The encoder that I was using is a EVQ-WTE series encoder manufactured by Panasonic.  The encoder act just like typical 2-bit quadrature encoders with A/B outputs that are out of phase by 90 degrees.   The encoder has 30 mechanical detents for each revolution of the knob but only produces 15 complete output cycles.

The encoder waveforms look like this:

            +----+----+------ Mechanical Detent
            |     |     |
            V     V     V        
      ---+     +----+     +---
  A      |     |     |     |
         +----+     +----+

         ---+     +----+     +---
  B         |     |     |     |
           +----+      +----+
              ^         ^
              |         |
              +--------+------ HSC counts here

  A/B Phase relation for C.W. Rotation



I tried 2 different approaches to interface this encoder to the PLC:

1.  Ladder logic.  This failed because the "debounce" logic used for the PLC INPUT circuits limits the speed that the the encoder can be operated and the ladder logic scan time is a  too slow to catch all of the transitions on the A/B inputs.

If the knob is turned quickly at a speed of about 1 RPM the phase difference of A/B can be as little a 2.5 ms.

I used the following ladder logic.  I used a Sequencer because it is easy to initialize to a value of "0" without having to use a custom function.


 |
 | 1st.Scan                              Seq1:0
 +-----||--------------------------------[StepN]
 |
 |     A                                  CLKA
 +-----||--------------------------------[dDIFU]
 |
 |      A                                 CLKAN
 +-----|/|-------------------------------[dDIFU]
 |
 |    CLKA     B                          Seq1
 +-----||-----|/|---+--------------------[Upctr]
 |                   |
 |    CLKAN   B      |
 +-----||-----||----+
 |
 |    CLKA    B                           Seq1
 +-----||-----||------+-----------------[Cnctr]
 |                    |
 |    CLKAN    B      |
 +-----||-----|/|-----+
 |
 |


2. High Speed Sequencer.  Using HSCDEF 2,2,32000 in a custom function and connected the A and B phase signals to input pins 5 and 6.

The high speed sequencer only counts on the positive transitions of the A phase.   As a result, for every two clicks (mechanical detents) on the encoder the HSCPV[2] will count up/down only one time.  

The good news is that the HSC mechanism is fast enough for my low speed counter application.  Unfortunately the HSC only counts 1/2 of the time!

3. My next experiment is to use both HSC #1 and HSC#2 to connect to the mechanical encoder.  I will connect the encoder A/B inputs directly to HSC #1.  I will connect inverted versions of A/B (ULN2003?) to HSC #1.  I will then use a custom function to calculate the total count T:

    T = hscPV[1] + hscPV[2]

QUESTION  1:

Is there a mechanism to configure the High Speed Counters for the M series of the F series to count on both transitions of the A phase?  Look at my ladder logic for an example of how this is done.


QUESTION 2:

Do you have any other suggestions on how to get a low speed quadrature encoder to work with your PLCs?

QUESTION 3:

Is there some easier mechanism for me to draw waveforms on your YaBB system?  I change the fonts to "Courier" but your BB system has issues with ASCII spaces (0x20) and does not treat them as having the same horizontal width as other printable characters.  This makes it impossible to do nice ASCII artwork.

Thanks,

Gary D.

You can use ladder logic to create OUT2 so that it is ON for the first 30 seconds that OUT1 is ON.

You can use a TIMER with a Set Value of 300 (30 seconds) to generate OUT2 from OUT1.

In the following example, Tmr30Sec is a TIMER with a SV of 300:


   Out1                                  Tmr30Sec
----||------------------------------------(TIM)

   Out1   Tmr30Sec                        Out2
----||------|/|---------------------------(OUT)



There is sample code posted on the TRI website that demonstrates how to set/clear many relays based on the current time.  I use this code in all of my PLC projects and it is 100% reliable.

http://www.tri-plc.com/trilogi/RTCAppByGDK.zip

Gary D.