how to get RPM from encoder vi?

[PSong]

Hello there 🙂

i am new for labview and facing problem about how to get rpm speed from encoder vi.

for this project, requirement is getting dc motor current and speed rpm.

here is the code i done so far.

i know the equation that use to get rpm is 

(current count - previous count)/PPR/time interval

1. about PPR

in my case, my motor CPR=57.675 but i need to use PPR. since PPR=CPR/4, so my PPR = 14.41875

am i doing correct about this?

2. about time 

i am not so sure that what is time interval and how to get it?

however, from the code, i can measure time while this vi running. (time counting in code)

finally, rpm shown some value that not correct. the speed of this motor when no load is more than 700 rpm.

i have no idea how to fix it. hope you guy can help me.

in addition, the current that i got is quite slow when compare with the version that i didnt use case structure.

is this because of case structure?

thank you in advance

[vardanium]

time interval is the time window between two counts (it could be for example the time of iteration of 1 loop). For the rest, you've done correct. I suggest to check the results you got with another software, or for example microcontroller (pic, Arduino, etc.). I suppose the HW isn't working correctly. 

Also, I'd suggest to test this with cRIO FPGA target. It might happen, that cDAQ is a bit slow and cannot register all instances of movement signals. 

[PSong]

Hi vardanium

thank you for reply. Could you tell me more abt what is FPGA target?

right now i am using only myRIO.

[PSong]

and i still dont get about time iteration for 1 loop.

it could be great if you have some example.

Thank you