Long distance temperature measurement

[mohansaini]

Hi All
I have to measure temperature of a DG(Diesel Generator) canopy by using a Microcontroller which will be around 5-10 meters from the DG to a control room.For that purpose wire length will be increased previously i was using 10K NTC which was not so far from the MCU. if i go for the same due to wire length change in resistance will be effected and will effect output so please suggest how can i achieve that.
Can i use LM35 which has a input range from 5-30V but output of LM35 will be the another problem.


Thanks.

 

[betwixt]

What temperature range are you expecting. A thermistor can have a much greater range than an LM35. If you are measuring below 125C I would suggest using a 1-Wire sensor such as the DS18B20 which will take an accurate reading and with care can send the measurement over 10 meters without any problem. I use them with a local interface (PIC10F202) to send data over several hundred meters.

Brian.

 

[mohansaini]

Temperature range would be from 0 to 100 deg C only. DS18B20 is a digital serial sensor is it easy to read its output. I mean to say that the output format has some standard or its simple binary to decimal conversion. Please suggest its working circuit if any.

 

[betwixt]

It's easy to read but it uses 1-Wire protocol, most compilers have functions to read them and if you are writing in assembler the code is fairly easy. Full details are in the data sheet.

The you can set the number of bits resolution you need but it does take a short time (~750mS) to return a measurement if you use the highest resolution which is 0.0625 degrees. It is very easy to use lower resolution and because 0.0625 = 1/16 you can easily shift the bits in the result to get whole degrees and fractions without having to do multiplication or division. You can also wire more than one sensor in parallel and still take reading from each separately.

Brian.

 

[mohansaini]

Which supply i.e. 5V or 12V with refrence to GND i have to chose for its input for long distance say 10Meters. for more than 1 sensor on a single line is there any specific ID arrangement.

 

[dv_sa559]

I think you can use PT100 or PT1000 for this project (RTD sensors). 3 or 4 wire RTD sensors can sensing temperature at long distance, whoever 2 wire sensors rtd can measure temperature with a little tolerance. you can simply connect rtd to your micro controller and measure temperature.
https://www.edaboard.com/threads/179422/
https://www.edaboard.com/threads/252052/

 

[betwixt]

The DS18B20 series all work from 3V to 5V and connect via three wires, 1-ground, 2-supply and 3-data. They only draw about 1mA. It is possible to connect them using two wires, there is information on this 'parasitic' power method in the data sheet. All devices have a factory programmed serial number which you cannot change, you can address an individual device by sending a 'select' command followed by the serial number, only the matching device will respond.

Brian.

 

[dick_freebird]

If you use a 4-wire Kelvin setup and an automotive grade
thermistor (like an ECT sensor) then you can forget about
wiring contribution to the resistance measurement. But with
kilohm-range resistances where you care about the value,
those drops are probably negligible anyway. And automotive
apps tend to have a couple meters worth of harness between
PCM and sensor, with no ill effect. Not as if a couple degrees
of indicated water jacket temp is going to kill you.