# data logger question.



## 10492 (Jan 4, 2010)

On a analog input, what is the difference between single ended, and differential inputs?

I have some photo cells to log. Photo cells change resistance when light is applied. I want to log a couple of them together.

Would I need a logger with more single ended, or more differential inputs?

Thx.


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## Frank Mc (Nov 7, 2010)

Dnkldorf said:


> On a analog input, what is the difference between single ended, and differential inputs?
> 
> I have some photo cells to log. Photo cells change resistance when light is applied. I want to log a couple of them together.
> 
> ...


Hi Dnkldorf

Single ended inputs have a common ground whilst differential inputs dont...

Heres a link which may help
http://www.omega.com/techref/das/se-differential.html

I would say use single ended......I believe some data loggers allow you to connect either.
HTH
Frank


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## 10492 (Jan 4, 2010)

Cheers mate...:thumbsup:


Any tips for a logger, using this type of Photo Cell or something similar as the input?


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## Frank Mc (Nov 7, 2010)

Dnkldorf said:


> Cheers mate...:thumbsup:
> 
> 
> Any tips for a logger, using this type of Photo Cell or something similar as the input?


Havent used any loggers to date so cant recommend any particular unit...I did buy a multimeter recently that has the ability to log ..see link

http://www.hi-potential.com/products.asp?ID=73

Is this a home project...???

Im going to be doing a project using a linear light sensor....

http://www.futurlec.com/Light_Sensor.shtml

HTH
Frank


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## 10492 (Jan 4, 2010)

Hey Frank. this is a "shop project".

I have a trending meter, but it's only single channel.

For this project, I am looking at installing 36 photocellls in a room. 6 on each wall, cieling and floor.

I will put a post light in it, turn it on, and record the data. I was hoping to export it to an excel program, and graph the results.

It would allow me to see how the reflectors I am building are working.


I think the photocells I ordered will max out at 10 lux. I may have to try something else that would sense 50 FC, not 10 lux.


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## Jlarson (Jun 28, 2009)

Dnkldorf said:


> Any tips for a logger


I don't know what type of budget have for your experiment but these guys have always been good for logging data collection stuff. 

http://www.microdaq.com/

for what you have planned I'd look specifically at these

http://www.microdaq.com/measurement_computing/index.php


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## 10492 (Jan 4, 2010)

Jlarson said:


> I don't know what type of budget have for your experiment but these guys have always been good for logging data collection stuff.
> 
> http://www.microdaq.com/
> 
> ...


Thanks.:thumbsup:

I figure a grand, maybe 1500 for the right logger and software.

I need soemthing expandable to 32 or greater inputs. 4 on each surface plane would give me 24 inputs min.


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## Frank Mc (Nov 7, 2010)

Hi Guys

Wow ..thats a lot of channels to log....Have a look here as well...pity you need so many channels they have an 8 channel for $50.....

Are you capturing the light level at switch on ? or monitoring the level once turned on ...??

http://www.dataq.com/index.html

HTH
Frank


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## 10492 (Jan 4, 2010)

Frank Mc said:


> Hi Guys
> 
> 
> Are you capturing the light level at switch on ? or monitoring the level once turned on ...??
> ...


I am hoping both. 

Boy, It might make sense to get a couple 16 channel inputs, run two identical tests, and blend the results.

Hmm.....

What are you doing with that linear input optical sensor?


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## Frank Mc (Nov 7, 2010)

Dnkldorf said:


> I am hoping both.
> 
> Boy, It might make sense to get a couple 16 channel inputs, run two identical tests, and blend the results.
> 
> ...


Im just making a homebrew micro controlled light sensor which will have a couple of relays and maybe a serial interface....Need to hook it into my Home Automation Controller (Homevision) so i can active a flag to let my internal pirs trigger my lights at night time . Currently i use a scheduled event to set the flag.......

Frank


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## 10492 (Jan 4, 2010)

Update and question.

Rcvd the photcells and played with them a little with a meter and lights.

Hooked up a E-lite battery (6v) and measured the current (ma) change.

So, my question is:

If the data logger is capable of having 4-20ma signal inputs, will this input see a 1.5-30 ma signal, and record it?

Thanks.


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## Frank Mc (Nov 7, 2010)

Dnkldorf said:


> Update and question.
> 
> Rcvd the photcells and played with them a little with a meter and lights.
> 
> ...


I believe it wont record anything less than 4mA and will max out at 20mA....
Maybe best to convert that signal to voltage....
Frank


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## 10492 (Jan 4, 2010)

Frank Mc said:


> Maybe best to convert that signal to voltage....
> Frank


How would I go about that, to work with the little loggers you posted earlier?

I read something earlier today about using a 250ohm resister to achieve the 4-20 window.

I wondering if anything under 4 won't register, and anything over 20 wouldn't register, but I could scale it somehow using a small resistor to each pc. Do you think 30ma would fry the logger?


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## Frank Mc (Nov 7, 2010)

Dnkldorf said:


> How would I go about that, to work with the little loggers you posted earlier?
> 
> I read something earlier today about using a 250ohm resister to achieve the 4-20 window.
> 
> I wondering if anything under 4 won't register, and anything over 20 wouldn't register, but I could scale it somehow using a small resistor to each pc. Do you think 30ma would fry the logger?



You need to connect the LDR (photocell) via a resistor to say 5v and take readings of the junction point....Have a look here i havent checked it out fully but it should help....
http://www.ladyada.net/learn/sensors/cds.html

HTH
Frank


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## Del (Feb 10, 2011)

*Photocells*

It sounds like your doing some product testing.

Why not just plot a grid in the room, and move one cell around, yes it will take a bit longer, but it works.

A few years a go I had to design a 400Kw Infra Red oven for drying the sills on a car plant( manufactuturer now defunct). we did not have the full body just a small curved piece(secrecy). but with a few weeks of simulation under a IR unit, we could predict the bake temp. They had no temp controls other than the speed of the line- which never changed. Got to target temps on first real run out- once they sprayed the body the correct colour- yee haw.


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## Hunter1151 (Nov 4, 2010)

Try this
http://www.redlion.net/Products/ProcessControl/ModularController.html

This works extremely well, you can do a lot on here, software is free and simple, this is also a protocol converter, over 200 drivers, and data log is in .csv so any spreadsheet program can read this. Download software and try it.


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