To get accurate readings, every 1ms copy the HSC input to a circular buffer.

Every 2-10 ms (figure out what time makes for a smooth speed value), calculate the speed using values in the circular buffer and store to tag used for display/logging.

In the main OB, use the calculated speed for any further calculations and logging or display to HMI as required.

Calculate the torque in main OB from the speed calculated from your interrupt OBs.

The trick is do very little in the 1 and 2 ms interrupt OBs to capture and save the data.

Gybsen

Hi all.

I am trying to calculate torque (newton Meters) of  rotating drum speed up by a car ( when i am testing i use a small electric motor directly to the encoder)

I have an encoder with 400 pulses witch is configured to fourfold. The High speed counter works fine but i am having trouble to figure out how to make the program to be precise.

it would be best to have many measurements to get a nice clean curve, approx one calculation pr 50ms.

I have tried to use ob30 with 50ms interrupt, but not precise enough.

PLC = s7-1200 1212C  

Any suggestions???

Yes, calculate an average of all values in the circular buffer as  your current estimate of the RPM.

Since you have a noisy spot in your ramp, find out if it is signal or process by setting the rpm to something in that range and do the same test.  Then set it to 1/4 and 3/4 full speed and compare the traces.  I am guessing you have process noise and your encoder is seeing it.  Maybe a vibration analyzer can also sense the system response and compare where the vibration is highest in the rpm range.

If it is signal noise, be sure the encoder cable is properly shielded and crosses all high voltage lines at 90 degrees and is as far away as possible from them otherwise.

The encoder is counting and your system is calculating.  Unless you have a bad encoder, it is something causing bad pulses to be added or removed from the pulse train.

Gybsen

...

huggy_d1

That sounds like the thing i need. BUT....

I have only worked with pointers on s7-300, and as i learned today that is not the same in the TIA. Have no idea how to make a circular buffer..

Is your idea to calculate a average count from the circular buffer???

When should i reset the counter, at every 2-10ms interrupt???

on the following pictures you can see how i have tried, but failed.

Picture 1: Encoder counting curve, Smooth signal

Picture 2: Counting pr 10ms program

Picture 3: Counting pr 10ms curve.

As you can see on pic 3 the counting pr 10ms is NOT verry stable...