adccommunitymod (AutomationDirect) asked a question.
Created Date: November 30,2005
Created By: Jhsct
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Reality Check Required...Please help... I have a 1550 PPR Encoder (A only - Not Quad). The encoder has a 2.375 " Inch Friction Wheel riding on the conveyor. I'm feeding it into the H0-CTRIO Module on the DL06. Pulses are being registered by the unit and it seems to be working fine. However... I would like to have the input scaled for Rate...in Feet/Minute. The maximum rate will be 1600Ft/Minute. Before I got to that point, which I still have some questions, I hit a snag. My first check was to put in the 1500PPR in the Count Per Unit Box under the Rate Scaling in the Counter Workbench Software. I figured this should give me the RPM of the Conveyor. Either I'm missing something or the tach used in our lab is way off as the reading from the Encoder/PLC and the reading from the Tach are not even close. Is there something I'm missing? The encoder is directly coupled to the Friction Wheel so the RPM should be the same as the reading from the tach??? Thank you
Created Date: November 30,2005
Created by: GKiser
Jhsct,
Your encoder is 1550 ppr pulses per revolution, but the wheel it is tied to is a 2.375 inch wheel (I assume this is the circumference, correct?; i.e. one revolution of this wheel travels 2.375 inches?) You want your rate scale to be feet/minute. Thus:
12 inches / 2.375 ipr = 5.053 revolutions. In other words, it takes 5.053 revolutions of the friction wheel to equal 1 foot of travel.
In 5.053 revolutions, how many pulses will the encoder generate?...
5.053 r * 1550 ppr = 7831.5 pulses
Thus when the friction wheel has traveled 1 foot, then the encoder has generated 7831.5 pulses to the CTRIO input.
Thus in the Counts/unit enter 7831.5. Since you want the Unit Time Base in minutes, select minutes.
Now, to test it out use the Rate Scaling Calculator at the right. We now know that if we get 7831 pulses in one minute that will equal 1 ft/min speed. So...
Enter 7831 in "Counts in sample. " Enter 60000 in "Sample Time " (since it is in milliseconds). Now you see that the Scaled Value is 1 ft/m.
At 1600 ft/m, that would be:
1600 * 7831 = 12,530,526 ppm
If you enter that huge number in "Counts in sample " you will get 1600 ft/m in the answer.
The problem with this application, however, is that if you are going that fast, then this will generate pulses at a frequency of:
12,530,526 ppm / 60 = 208,842 Hz
The CTRIO input is only rated at 100 KHz; 209 KHz is more than twice that frequency. Thus I would recommend either a larger friction wheel, or a lower resolution encoder.
Hope this helps.
Greg Kiser
Host Engineering, Inc.
Created Date: November 30,2005
Created by: Jhsct
Reality Check Required...Please help...
I have a 1550 PPR Encoder (A only - Not Quad). The encoder has a 2.375 " Inch Friction Wheel riding on the conveyor. I'm feeding it into the H0-CTRIO Module on the DL06. Pulses are being registered by the unit and it seems to be working fine. However...
I would like to have the input scaled for Rate...in Feet/Minute. The maximum rate will be 1600Ft/Minute. Before I got to that point, which I still have some questions, I hit a snag.
My first check was to put in the 1500PPR in the Count Per Unit Box under the Rate Scaling in the Counter Workbench Software. I figured this should give me the RPM of the Conveyor. Either I'm missing something or the tach used in our lab is way off as the reading from the Encoder/PLC and the reading from the Tach are not even close. Is there something I'm missing? The encoder is directly coupled to the Friction Wheel so the RPM should be the same as the reading from the tach???
Thank you