Rising Edge Period Measurement | LabJack
 
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Rising Edge Period Measurement

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JHodg
jhodg's picture
Rising Edge Period Measurement

I am trying to measure a rising edge period of a 3 wire paddle wheel sensor I pulled off my boat.  Depending on the wheel's position the sensor reads out either 0.633 volts or 0.038 volts.  I am pretty new to this and am not quite understanding why the timer won't read out a period (in test panel, timer 0).  I did notice that as I connect/disconnect the signal wire or tap it on the terminal quickly a period will record.  Does the lowere end of the voltage readout have to cross the zero volts threshold to get the timer to read?

LabJack Support
LabJack Support's picture
Hello,

Hello,

You probably are having problems due to the high/low state thresholds: https://labjack.com/support/datasheets/t-series/appendix-a-2

What device are you using? you could amplify your signal to get above the threshold and that should fix things; the U6 and T7 have built in in-amps. We also have our LJTick-InAmp: https://labjack.com/accessories/ljtick-inamp

LabJack Support
LabJack Support's picture
A comparator would be a

A comparator would be a likely solution here:

https://forums.labjack.com/index.php?showtopic=2028

 

JHodg
jhodg's picture
I'm using a U3-LV.  I have an

I'm using a U3-LV.  I have an InAmp but can't figure out how to wire/configure this correctly.  The only way I've been able to measure an oscillating signal is to have the sensor positive and ground connected to the v-ref and ground of the amp and then the signal wire is connected to the INA-.  With my multimeter I get 4.7 and 4.105 but the test panel is showing a constant 2.5 on that channel?  I have dip switch #5 activated on the InAmp.  Is there a better way to wire/configure this?

I haven't tried a comparator yet as I don't have one readily available.

LabJack Support
LabJack Support's picture
The AIN on the U3-LV can only

The AIN on the U3-LV can only accurately measure 0-2.44V normally or 0-3.6V with a special setting, so what you are seeing sounds reasonable: https://labjack.com/support/datasheets/u3/appendix-a

I do not think the InAmp will work well for your application, I would recommend getting a hold of a comparator. Honestly, it was poor advice to lead with the amplifier suggestion, a comparator is what you should use for your application.

JHodg
jhodg's picture
10-4, thanks guys.  I really

10-4, thanks guys.  I really appreciat your quick responses and access to the forums (new and old) it's all very helpful and approachable.