LM35 Problem in Long Distance...

I have to measure the Temperature from the Room which is about 100 meters far from my device.
I am using PIC16F877A and LM35 and i am not getting output correctly some times high and some times low.
Not constant.
I have also used 75ohm and 1uF capacitor in series, but near to micro-controller.
But i am still getting the same problem..

The cable which is connected to sensor LM35 and my device is CAT5 cable.

Can anyone suggest me how to measure the temperature correctly.

I am also thinking to implement voltage to frequency conversion at the LM35 End and frequency to voltage converter at the controller end..
Please suggest me something.
To measure the temperature correctly

In my view you should conver the voltage in digital form at sensor end and then send it by some means of protocol.....But as you mentioned that your distance is 100 meter only ... Only the protocol that i know which works at such a long distance is internet protocol ( TCP/IP) ..... However .... I like your idea of making V to F conversion ...... But in that case the problem that you will end up with you need to have some concept of start of singal and end of singal need to protocoled....

Good Luck

Or convert the signal to a current.

Keith

use RS485 protocol...convert your LM35 data into RS485 and on the other side convert it back to display the temperature data
Keep your baud low...with 100kBaud, you can reach as close as 1000meter and use shielded twisted pair cable..

milind.a.kulkarni said:

In my view you should conver the voltage in digital form at sensor end and then send it by some means of protocol.....But as you mentioned that your distance is 100 meter only ... Only the protocol that i know which works at such a long distance is internet protocol ( TCP/IP) ..... However .... I like your idea of making V to F conversion ...... But in that case the problem that you will end up with you need to have some concept of start of singal and end of singal need to protocoled....

Good Luck

Click to expand...

Thanks for your reply....

I can't implement TCP/IP Protocol as i am not having much knowledge of that and that will also make my device much more complex.
Now for V to F conversion technique..
i will use LM331 IC as voltage to freq converter and then at the controller end i will use again this IC to convert back voltage from the frequency..

I want to kno. if i implement this, is it good or not.. will this pick noise may be my signal get distorted or this is the better way to implement long distance measurement

Pls reply

erio said:

use RS485 protocol...convert your LM35 data into RS485 and on the other side convert it back to display the temperature data
Keep your baud low...with 100kBaud, you can reach as close as 1000meter and use shielded twisted pair cable..

Click to expand...

Can you explain how i can do this...
I don't want to use controller at my sensor end...
Because my device is having 8 to 64 sensors.

arunsharma0731 said:

Can you explain how i can do this...
I don't want to use controller at my sensor end...
Because my device is having 8 to 64 sensors.

Click to expand...

Hi,

Think you ought to reconsider your choice of an Analogue sensor; the method of how to transmit an analogue signal over 100 m and how you intend to select and read in 8 - 64 analogue sensors on a device that only has 8 adc channels; at the end of all that you still expect the little analog signals to be accurate ..? !

Seems the Digital sensors from Maxim such as the DS18B20 are better suited, they can be individually addressed, capable of large transmission distances and many devices can be hooked to just one port pin.
**broken link removed**

milind.a.kulkarni said:

In my view you should conver the voltage in digital form at sensor end and then send it by some means of protocol.....But as you mentioned that your distance is 100 meter only ... Only the protocol that i know which works at such a long distance is internet protocol ( TCP/IP) ..... However .... I like your idea of making V to F conversion ...... But in that case the problem that you will end up with you need to have some concept of start of singal and end of singal need to protocoled....

Good Luck

Click to expand...

hai have you any examples to send that data in to tcp/ip ?

Why you use LM35. You can use ds1820 sensor and 1 wire protocol. it can used over distance up to 85m.

#MAAM# said:

Why you use LM35. You can use ds1820 sensor and 1 wire protocol. it can used over distance up to 85m.

Click to expand...

Actually i haven't search the sensor's other than lm35 over net, but now i am doing this..
and find DS18XX series...
Can i use DS1822 Sensor... but in its application note its programming looks very complicated..
But i will do this...

Thanks for advising me.. if some one can give me some more information regarding this sensor..

Thanks in advance