LM35 on fieldpoint

[jabsfar]

Hello all,
My knowledge is VERY limited, I've just started getting interested in FieldPoint for logging/control in a home automation project. I have no prior knowledge of electronics (but I'm desparately trying). I've succeeded up to now installing several counters and level detectors, but can't seem to get any reading from LM35's on my FP-AI-100. My problem is that I'm not sure where to connect what. Could someone please indicate to me to what terminal-numbers the three LM35 connectors should go ...
Thank you very much,
Amicalement,
Jan Bayer

[Matthew_Williams]

Hi Jan.  Welcome to the Fieldpoint world, congratulations on getting your other sensors working.

If the power supply you are using for the cFP controller is < 35 VDC, then you can use that power
supply for the LM35 as well.  If it is not, you will need a power supply that is < 35 VDC for the LM35.

The LM35 data sheet lists 35 VDC as the maximum allowable voltage, while one of the diagrams
shows 4-20VDC; I don't know which is correct, I suspect the 35 VDC, but it has been a long time
since I used any of these devices.  Whatever the maximum really is, as long as your cFP
controller supply voltage is lower, you can use it.

Connect the 'GND' terminal of your LM35 to the 'COM' terminal of one of your input channels.

Connect the 'Vout' terminal of your LM35 to the 'Vin' terminal of the input channel.

Connect the 'Vs' terminal of your LM35 to the 'Vsup' terminal of the input channel.

Connect the 'V' terminal of the connector block to the V1 (or V2, if that is where your power supply is
connected) of the cFP controller.

Connect the 'C' terminal of the connector block to the 'C' terminal on the cFP controller.

If your cFP controller power supply is > 35 VDC, you will need an external power supply that
is connected to the 'V' and 'C' terminals in the connector block, with no connection to the
controller terminals.

Configure the input channel for voltage, start with 0-15 V and work your way down.

This will allow you to measure positive temperatures up to the limit of the LM35.

cFP-AI-100 data sheet: http://www.ni.com/pdf/manuals/370278a.pdf

LM35 data sheet: http://www.national.com/ds/LM/LM35.pdf


Hope this helps.  Let us know how you make out.

Matt

edit: all the same applies to FP same as cFP.


Message Edited by Matthew Williams on 01-27-2008 05:28 PM

[jabsfar]

Hi Matthew,

Thank you very much for your extremely rapid response ! I already feel welcome ...

It turns out I had inverted the Com and Vsup terminals on the LM35. I admit I do not complete grasp the V1 and V2 part of the story, but it is probably what made my LM35 heat up like crazy when I decided to try and inverse them in my system.

I now have the feeling that my LM35 responds to heating by decreasing the voltage output, which I think is pretty strange ... Fluctuations seem to be (well) within 10 mV for the moment. I can probably improve by building a more sophisticated circuit, as indicated in the documentation you sent me, and using proper wiring. I'd have to buy some components, and a soldering iron ...

I'd be happy to tell you in a little more detail what I'd ultimately like to do, but the forum is probably not the place to do so.

Thanks again for your perfect help,

Amicalement,
Jan

[Matthew_Williams]

Hi Jan,

V1 and V2 are alternate voltage inputs.  The controller will run from whichever has a higher voltage.
We supply 28 VDC from a mains connected supply to V1 and 24 VDC from a UPS connected
supply to V2.  When the mains fail, the controller automatically switches to the UPS supply.

Decreasing voltage with increasing temperature doesn't sound proper; should be the other
way around.  Something still isn't quite right.  Do you have another LM35 to test with?  I don't
know how tolerant of a reversed supply voltage the units are.

If you would rather do further details offline, you can email me at forum@mackinfo.com.

Matt

[jabsfar]

Matthew,
Hope you read this. A short message to tell you that all works fine now ! It turned out that my first LM35 was indeed "burnt", a victim of my inexperience. I couldn't reach you on your direct mail, but anyway, all is fine now.
jan.bayer@free.fr
Amicalement

[BOLANTOY]

hi gd day to everyone....i just to get help out there...currently im working on a digital thermometer project..i have a limited background electonics...im want that my output of my sensor is ranging from 5 celcius to 50...does anyone knows how to calibrate it...thank so much....

[Matthew_Williams]

Hi Bolantoy.  If you are using an LM35, the output will be 10 mV/C, so 5C will be 50 mV and 50C will be 500 mV.
Does that answer your question?  If not, please post back.

Matt

[BOLANTOY]

yeah...i mean can give me some circiut...cause i reall dont know how to make the circuit...thanks for the help...

[Matthew_Williams]

There are several example circuits in the LM35 pdf file linked above, look for 'Typical Applications' part way through.

Matt