Easy datalogger?

[MikeLip]

I am using one to measure amps fed to a motor. I did this with a current transformer, a burden resistor, a simple rectifier and a capacitor. You pass a supply wire through the transformer, develop a voltage from it across a resistor, rectify and filter the voltage.

The transformer came from CR Magnetics - it's a 1:1000 job, which means it puts out 1mA for every amp flowing through the supply wire. Put a 1000 ohm resistor across it, and you have an output of 1VRMS per amp. You can use whatever resistor fits your current range and the range of the A/D.

The rectifier and cap turns that into DC and averages it, so you have a clean DC level to look at with the A/D. You need to pick a capacitor and a bleed resistor value that will give you a time constant that will allow you to see changes at a rate that seems to make sense.

Mike

 

[jtice]

Well, heres alittle update...

My light meter outputs 1 mV for 1 unit on its display....
BUT, the logger is not very accurate at low V, so, I hear I need to make an opamp, to boost the signal from the meter.
I can also build an adjustment pot into the opamp.

Now, for the software,,,
what comes with it is ok I guess, though its not real user friendy and I cant seem to figure out alot of the options.
I dont understand why I cant tell it to scale the #, or calibrate it much.
I see a calibrate funtion, but it has all this high low crap, and I have no idea what its talking about.

I wish I could just tell it, that if the meter outputs this,,, log this.
But I guess I can use excel to convert all that.

lymph, I would LOVE to be able to get it to import straight to excel, that would save me the step of copying the data into excel manually. Will it do it in real time? I think there is other software on their site that lets me do that, but its over $100 i think. /ubbthreads/images/graemlins/frown.gif

Also, its logging the data in scientific form, id like to get that in just normal #s. I couldnt even get excel to convert it properly.

so I need to fix...
boosting the light meters output to a higher V so the logger reads it more accurately.
Add an adjustment to the opamp so I can fine tone it.
Make it easier, and less steps to get the data to excel.
Get it to output normal #s.

~John

 

[MikeLip]

[ QUOTE ]
jtice said:
Well, heres alittle update...

My light meter outputs 1 mV for 1 unit on its display....
BUT, the logger is not very accurate at low V, so, I hear I need to make an opamp, to boost the signal from the meter.
I can also build an adjustment pot into the opamp.


[/ QUOTE ]
Bummer - but a single ended opamp should be OK - by that I mean something that runs from a single supply. Check Digikey or something. The amp and a couple resistors should do OK for you.
[ QUOTE ]

Now, for the software,,,
what comes with it is ok I guess, though its not real user friendy and I cant seem to figure out alot of the options.
I dont understand why I cant tell it to scale the #, or calibrate it much.

I see a calibrate funtion, but it has all this high low crap, and I have no idea what its talking about.

I wish I could just tell it, that if the meter outputs this,,, log this.


[/ QUOTE ]
What you do is you put in a known input and tell it what to call it. You do this in edit > high and low calibration. Put a zero value into it and set low cal to zero. If you are using a single ended opamp circuit, you won't get to zero - no matter, ground the input to your circuit, and tell the A/D that what is coming out is zero. That will take care of the offset. Put a known voltage into it and call that high calibration - for instance, if you know that you will be seeing 200mV for 100Lux, you give it 200mV and tell the high cal that this is 100 - you can also name the units. You also tell it the limits or span - if you are looking for a 0 to 5 volt signal, you can tell it only to look at say -1 to 6 or something similar to let you see over/undershoot. You do this in scaling->limits. This sets the amplitude span of the chart display, so the reading isn't compressed needlessly.
[ QUOTE ]

But I guess I can use excel to convert all that.


[/ QUOTE ]
Never done that, sorry.

Mike

 

[jtice]

Mike,, thanks alot !@!!!!

I will try that calibration when I get home, that might help a good bit.
I like how I can tell it so many mV actually = so many Lux.

What is yours outputting in? Is it a scientific # also?

 

[MikeLip]

I just take my readings from the strip chart - I am using it to monitor long term motor performance; speed, current consumption, temperature and blower pressure. The data is recorded a week at a time so I can go back and look for signatures if the motor fails, since typically there is little left of the motor afterwards! My needs are a bit different, since I am testing a 15,000RPM 1HP motor /ubbthreads/images/graemlins/grin.gif But the aquisition unit I use (which I pointed out and you bought, apparantly) should be able to handle the type of testing we're interested in with no problems beyond a bit of adaptation.

Mike