10-02-2011 03:55 PM
Hi, as part of a of a program im writing I have to measure the speed of travel of a linear transducer. The transducer is attached to a hydraulic cylinder/actuator and has the same travel as the hydraulic cylinder. The hydraulc cylinder speed of travel is controlled by a proportional valve and by varying the voltage input to this valve will increase or decrease the speed of the cylinder. The opposing load on the hydraulic cylinder is varying which causes the speed of the hydraulic cylinder to speed up or slow down, to prevent this i have to vary the control voltage to the proportional valve to maintain a steady speed. I would like to use the input from the linear transducer to control this but im not sure how to measeure the speed as it is a voltage input. If i can some how convert the voltage input to a millimetres per second or something like that, i think this would be a start, any help would be great.
10-02-2011 04:26 PM
When you say you have a linear transducer, exactly what do you mean?
Is this a position transducer like a linear potentiometer which has an analog output voltage proportional to the position? Or some other type of transducer?
Do you know how to measure the voltage input? Do you know the transfer function of the transducer?
How fast can the cylinder move? How often do you need to update the control valve voltage? Do you need to control the speed in both directions? How much noise do you have in your measurements?
What parts do you have working and what are you just planning? What have you tried which did not work? What did not work about those things?
10-02-2011 05:30 PM
10-02-2011 06:54 PM
OK. Slow is good.
To get a measure of speed think about the units: velocity = distance/time. So if you subtract the position at t1 from the position at t0 and divide by t1-t0, you get a velocity. Like any differentiation process it tends to emphasize any noise or variations.
You want to update the control voltage about every 12 seconds. I suggest that you read the transducer voltage once per second and keep a running average. Then every twelve seconds use the value of the average to adjust the control voltage. The averaging process will smooth out small variations due to electrical noise, vibration of the cylinder or transducer, and imperfections in the transducer.