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Type of sensors to use


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3 replies to this topic

#1 Markw

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Posted 28 July 2014 - 02:24 AM

Hi all.

I have purchased a U3 HV and I am wanting to us it to measure an RPM with a pulse count up to a max of 10'000 rpm and the reading from a load cell.

What type of sensor would be best for the rpm count and will I need the LJtick current shunt for the load cell? How would they be connected? The main problem is I don’t know much about electronics but I am wanting to learn.

The project is connecting my engine dyno to my pc to get a read out instead of doing all the calculations manual y.

Any help is much appreciated





#2 LabJack Support

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Posted 28 July 2014 - 11:18 PM

Here is an introduction to RPM measurement: http://www.opto22.co...hnical_note.pdf


There are a lot of ways to go about this. If the engine already has sensors then tapping into those signals is usually easiest. If you have to add a sensor then options range from crank position to a simple inductive once per revolution pulse sensor. I'll ask around over here to see if anyone recommends a specific sensor.

#3 Markw

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Posted 30 July 2014 - 03:54 AM

I would like to have a seperate rpm pickup so when the engine is changed I dont have to change the pickup or reclaabrate anything. It will be easy enough to fit a disk with 1 or more teeth for the sensor.

Will go and read the link.



#4 LabJack Support

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Posted 30 July 2014 - 10:11 AM

Once you get some sort of sensor that gives you some sort of pulse signal, you have to look at whether that pulse signal can connect directly to a U3 digital input, or whether it needs some signal conditioning.  The input low logic level of the U3 is -0.3V to 0.8V and the input high logic level is 2.0V to 5.8V:




If your voltage levels are bigger, you might need a voltage divider.  If smaller, you might need a comparator.  You also need to consider whether the signals are push-pull, open-collector (NPN), or something else:





Once you have a signal with valid logic levels, see the following forum topic about frequency measurement:




With the U3, I suggest you try a timer in the 32-bit Period mode.  Start by trying it in the test panel in LJControlPanel.



If your load cell is a typical raw load cell, that means it is simply a bridge circuit.  The U3 will need an LJTick-InAmp to get readings from a bridge circuit:





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