Speed Measurement using Proximity Sensor

[Redox_07]

Hello LV Board,

I am using Waycon IC18-08 Inductive Proximity sensor for determining the speed of rotation of DC Motor. I am using NI 9203 to acquire 4-20mA current output through NI cDAQ9184. I have the following queries:

1. I am planning to use AI0 for speed sensing and AI1 for Torque-Sensing. Is NI9203 capable of recording channels simultaneously? 

2. I checked the output of the Proximity sensor with the input of ~15V giving constant output amplitude at 0.214 and dipping every time the metallic strip passes in front of it. What should be the sampling rate ideally should I use to sense speed change within (say) 5 seconds?

3. How do I implement increment counters in the program every time the output of proximity sensor dips below a threshold? what should I set as a threshold? (given the amplitude 0.214 at no metal sensed)

I would be grateful if the code for the same may be shared.

Thanks

[GerdW · Accepted solution]

Hi Redox,

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@Redox_07 wrote:

I am using Waycon IC18-08 Inductive Proximity sensor for determining the speed of rotation of DC Motor. I am using NI 9203 to acquire 4-20mA current output through NI cDAQ9184. I have the following queries:

1. I am planning to use AI0 for speed sensing and AI1 for Torque-Sensing. Is NI9203 capable of recording channels simultaneously? 

2. I checked the output of the Proximity sensor with the input of ~15V giving constant output amplitude at 0.214 and dipping every time the metallic strip passes in front of it. What should be the sampling rate ideally should I use to sense speed change within (say) 5 seconds?

3. How do I implement increment counters in the program every time the output of proximity sensor dips below a threshold? what should I set as a threshold? (given the amplitude 0.214 at no metal sensed)

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1. The NI9203 uses a MUX to switch between its channels: you can measure not exactly simultaneously, but one channel after the other at your desired sample rate.

2. Required sample rate is dictated by Mr. Nyquist and Mr. Shannon: you need to sample at least at twice the expected maximum frequency. (It's recommended to sample at about 5-10× f_max.)

3. The threshold should be set below your "flat line amplitude" of 0.214 (which unit?) and above the "dip below". Think about possible added noise. To implement a simple counter you should use a shift register…