using the LM 35 in a temp sensor

[Johan Wagener]

I have decided to use the LM 35 as the sensor in my temperature
monitor.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

I need a accuracy of about 1 degree Celsius.

I also need an sensitivity adjuster and an offset adjuster

Thanks for any help.

I am designing this circuit in crocodile physics

 

[John Larkin]

On 18 Mar 2004 07:53:49 -0800, johanwagener@webmail.co.za (Johan
Wagener) wrote:

I have decided to use the LM 35 as the sensor in my temperature
monitor.

Don't run it from more than +5 volts; don't do the below-zero pulldown
thing; avoid any capacitive loading. Tricky part.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

Why do you need a current source?

I need a accuracy of about 1 degree Celsius.

The accuracy is on the datasheet.

I also need an sensitivity adjuster and an offset adjuster

Thanks for any help.

I am designing this circuit in crocodile physics

John

 

[John Woodgate]

I read in sci.electronics.design that Johan Wagener
<johanwagener@webmail.co.za> wrote (in <c86a2c09.0403180753.4ce8e29f@pos
ting.google.com&gt about 'using the LM 35 in a temp sensor', on Thu, 18
Mar 2004:

I have decided to use the LM 35 as the sensor in my temperature monitor.

Get the data sheet from the NS web site.

What will the circuitry around the IC look like?

What don't you understand about the data sheet information?

Can I use a howland
current source in this design?

What for?

I need a accuracy of about 1 degree Celsius.

See the data sheet.

I also need an sensitivity adjuster and an offset adjuster

Figures 10 and 12 on the data sheet give clues on how to do this.

Thanks for any help.

I am designing this circuit in crocodile physics

You want a snappy design? (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Peter Bennett]

On 18 Mar 2004 07:53:49 -0800, johanwagener@webmail.co.za (Johan
Wagener) wrote:

I have decided to use the LM 35 as the sensor in my temperature
monitor.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

I need a accuracy of about 1 degree Celsius.

I also need an sensitivity adjuster and an offset adjuster

Thanks for any help.

I am designing this circuit in crocodile physics

Go to http://www.national.com and get the LM35 datasheet.

Basically, you apply 5 volts or so between the power and ground pins
(no need for any external current source), and measure the output
voltage, which will be 10 mV per degree C, if I recall correctly.


--
Peter Bennett VE7CEI
email: peterbb (at) interchange.ubc.ca
GPS and NMEA info and programs: http://vancouver-webpages.com/peter/index.html
Newsgroup new user info: http://vancouver-webpages.com/nnq

 

[Nico Coesel]

johanwagener@webmail.co.za (Johan Wagener) wrote:

I have decided to use the LM 35 as the sensor in my temperature
monitor.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

Why? These temperature sensors work like a zener diode. Just power it
through a resistor which keeps the current within specs over the
measuring range.

I need a accuracy of about 1 degree Celsius.

I also need an sensitivity adjuster and an offset adjuster

Use an LM335 instead and you won't need any adjustments.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[Chaos Master]

No B.O. número <c86a2c09.0403180753.4ce8e29f@posting.google.com>, de 18 Mar 2004
07:53:49 -0800, consta que Johan Wagener escreveu no sci.electronics.basics :

I have decided to use the LM 35 as the sensor in my temperature
monitor.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

I need a accuracy of about 1 degree Celsius.

I also need an sensitivity adjuster and an offset adjuster

Thanks for any help.

You don't need a current source.

Basically, you just give the chip 5V on the appropriate pin, ground the ground
pin and get 10mV/°C (IIRC) on the output, and you can feed this to any other
component (say a comparator).

Get the full datasheet from www.national.com .

[]s
--
Chaos MasterŽ - Porto Alegre, RS, Brazil
irc.brasnet.org - #xlinuxnews and #poa
marreka.no-ip.com (ainda năo pronto)
LRU #327480

 

[Robert Baer]

John Larkin wrote:

On 18 Mar 2004 07:53:49 -0800, johanwagener@webmail.co.za (Johan
Wagener) wrote:

I have decided to use the LM 35 as the sensor in my temperature
monitor.

Don't run it from more than +5 volts; don't do the below-zero pulldown
thing; avoid any capacitive loading. Tricky part.

What will the circuitry around the IC look like? Can I use a howland
current source in this design?

Why do you need a current source?

I need a accuracy of about 1 degree Celsius.

The accuracy is on the datasheet.

I also need an sensitivity adjuster and an offset adjuster

Thanks for any help.

I am designing this circuit in crocodile physics

John

I run them with a standard 9V battery all the time, and reliably (and
accurately) measure temperatures from 40C to 200C.
What makes you think ther is a problem above 5V?

 

[John Larkin]

On Fri, 19 Mar 2004 11:14:20 GMT, wouter@voti.nl (Wouter van Ooijen
(www.voti.nl)) wrote:

don't do the below-zero pulldown

why not?

The LM35-series parts are very prone to latchup. The triggers are

Pulling the output low before Vcc is up

Noise spikes induced into the output.

Vcc spikes, possibly

They'll do this at any Vcc, but above about +8 or so adds another
latchup mode, where the output goes to +6.8 or something, as I recall;
this could damage an ADC or something.

Bob Pease told me he'd get this fixed, about 10 years ago.

They also like to oscillate with capacitive loads.

John