peak voltage detector Automation direct 06

[bill hanson]

Hello all- I have a unique challenge using a customers Direct logic 06 PLC. This customer has a DC motor operating at 10 RPM which is turning a shaft that has a notch machined into it . The customer has a Keyence fibre optic unit that is set up to look across the shaft with the idea that the fibre receiver will see no light until the notch in the shaft allows light to pass as the shaft rotates. As the notch begins allowing light to pass, the keyence unit begins to output an analog signal in proportion to the degree that the notch is exposed as the shaft continues to rotate. When the shaft notch reaches its maximum exposure to the fibre light , the keyence unit will also be outputting the maximum output voltage to my analog input card. The trick is that the customer wants the motor to stop turning the shaft at peak voltage from the keyence unit.........here's the rub he wants the "peak" voltage, not a preset number as light values /dirt /ect may cause a set value to change, whereas a "peak" is the highest value for that particular rotation ...clear as mud?? Help if you can- Bill

 

[drbitboy]

"Peak voltage" implies a time period, and in this case over a range of motor positions, over which the voltage has multiple samples, and you cannot know the peak voltage until the final sample. So if the final sample of that time period, i.e. of the motor motion, is not the peak voltage, then the motor is past the peak voltage position, and must rotate backwards. Can it do that? How is motor positions controlled? What about inertia?

There also may be noise to consider, which will make this more difficult.

It might be possible to characterize the approach to peak voltage and predict the upcoming position of peak voltage, but being able to control the motor position in both directions would probably be better.