Can QD62 be used to measure the rotation speed (RPM)?

[imseng 0]

Hi Guys, I have a project of modifying an existing system that will have to put a new inverter and synchronize it with the existing Main Line Rotating Shaft. The existing system is using Q01CPU and it has 3 spare slot that I can use to put a new module and modify the program. What I need is to install an incremental rotary encoder and read the rotation speed (in rpm) and then send an analog signal as the speed reference to the new inverter. I was thinking of putting QD62. However after reading the QD62 Manual I don't see any particular function that referring to reading the rotation speed. I have done programming using FX2N and FX3U, and it was very easy to read the rotation speed by using SPD command. So, now I'm wondering whether I can use QD62 or should I use other module? Can someone enlighten me on this one? Thank you very much guys! Cheers, Kaew

[JRoss 84]

If you use the Sampling Counter Function, it should give you the same information as SPD in the FX series. You set up a period, and it gives you a count of pulses during that period. EDIT: Just to be clear, that is a function on the QD62 card itself, set up and monitored using the buffer memory locations. Edited 30 Aug 2010 by JRoss

[imseng 0]

Hi JRoss, Thanks for your reply. By using this Sampling Counter to read the RPM, is it okay that I create a periodic PULS timing that will enable counter (at Y06) without any "empty time space" (I don't know if this is the correct word). As this is meant for Sampling not periodic? Is the buffer can be refreshed and read immediately as T time is reached but at the same time the periodic PULS is also generated? Please advise. Thank you.

[imseng 0]

Hi JRoss, Thanks for your reply. By using this Sampling Counter to read the RPM, is it okay that I create a periodic PULS timing that will enable counter (at Y06) without any "empty time space" (I don't know if this is the correct word). As this is meant for Sampling not periodic? Is the buffer can be refreshed and read immediately as T time is reached but at the same time the periodic PULS is also generated? Please advise. Thank you.

[JRoss 84]

Unfortunately, those functions will conflict with each other. The Sampling Counter function must see a "rising edge", which means that Y06 must go off then on again. I think that's what you mean by "empty time space". It isn't the space that's important, but the rising edge. However, after looking at the functions closer, the Periodic Pulse Counter function is actually closer to the FX-Series SPD command, so I would recommend using it instead. Hopefully that simplifies things. Do you have access to the High Speed Counter User Manual? I can upload it, but I only have the North American version. Should be about the same, though the wiring diagrams are sometimes different since we use more sourcing over here.

[imseng 0]

Hi Jross, Thanks again for your email. Yes, that's what I'm worried if using Sampling Counter, because to keep, as if it continues reading the pulse, there will be conflict at the end of T periodic with the rising edge. I was looking into the periodic pulse counter too, but I have another question. To get a real time value at T periodic, I must have it by subtracting the present value with previous value buffer. But if the machine continues in operation, say for an extreme example, it is running continuously and at a certain time, the value of the pulse is incrementing (never decrementing), it may have reached its maximum value (32 signed bit), that it must go back to zero. I found it difficult when I must do subtraction. That's what my concern is. Any idea? Yes, I have the Manual Book of QD62. Thanks a lot!

[Carples 0]

can you reset the counter after each time period. What type of inverter are you using, more advanced inverters will have a pulse train input that you could use to feed the encoder signal into, and avoid the digital to analogue conversion. e.g. the Eurotherm 650 drives have an electronic gear box function that will track the line shaft position, with an electronic gear box function

[imseng 0]

Hi Carples, Thank you for your email. I don't know how to reset the counter (present and previous value), by using a software command. Or should I use external reset request? Then again the timing for reset request is very critical. The inverter that my customer using is Yaskawa Inverter G7A Series. I can't use the pulse train input, as I need to do some calculation inside the PLC which depends on the setting on the HMI and production request. And send the calculated number, which represent the speed as Analog Signal to the Inverter.

[JRoss 84]

iCreating the math for that kind of function is fairly simple. Here it is in pseudocode: PeriodicValue = PresentValue - PastValue If PeriodicValue < 0 Then PeriodicValue = PeriodicValue + 2,147,483,647 EndIf In Ladder, it would look something like this: |--------------------------------------------[ D- PresentValue PastValue PeriodicValue ]-| |-[ D< PeriodicValue K0 ]------[D- PeriodicValue K2147483647 PeriodicValue ]-|

[imseng 0]

Hi JRoss, Okay, thank you for your insight. Cheers,