Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

PT100 Calculations for temperature measurements

Status
Not open for further replies.
W

Wafeeq

Member level 3
Joined
Jul 26, 2010
Messages
61
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,288
Location
Pakistan
Activity points
1,728
Hello
i want to measure the battery surface temperature. please help me which temperature sensor will be fine for this purpose. i have the options of LM35 and PT100. which one is best.
 

Best in which regard? Pt100 offers highest accuracy without calibrating the sensor, LM35 offers most likely sufficient accuracy for your application. Best in terms of least effort also depends on the connected circuit. If you are dealing with positive degree C temperature only, both can be operated with a single additional resistor. Data processing is more easy with linear LM35 output than Pt100 that needs software linearization to get the exact temperature.
 

i just want to measure 0 to 100 C maximum, ambient temperature. i used LM35 in past but it is giving problem, its values drifts from it genuine values. it starts giving temperature more than the actual. i didn't ever use Pt100, i will need circuitry for this. i can read 2.5mV maximum from ADC. how to make voltage output from Pt100? do i need a amplifier of simple voltage divider?
 

Pt100 can be used with a simple voltage divider, but you have to calculate resistance from divider voltage in software, implies a division. The voltage divider circuit is most advantageous, if it uses the same voltage as the ADC reference (ratiometric operation). For a linear resistance to voltage measurement function, the Pt100 must be driven by a current source. The current through Pt100 must be restricted to avoid self heating of the sensor. 1 to 5 mA is a common value. Depending on the voltage range of your ADC, an amplifier may be required for maximum sensitivity.

Drifting measurements with LM35 seems to indicate a hardware problem, you shouldn't blame the sensor for it.
 

i used LM35 without any external circuitry. and there is no need of extra circuitry as per datasheet of lm35. below is circuitry i used to sense from lm35. please help if any extra circuitry needed for best performance of the sensor.. please find below snapshot of Proteus for reference.
View attachment lm35.bmp
 

The circuit is fine. You should observe the "decoupling from capacitive load" point in the datasheet, if you are using longer cables.

Also the 5 V supply should have a small bypass capacitor.
 

yup i have added a 100nF capacitor at 5V power supply. value of LM35 mostly drifts after year of working. it value drifts 4 or 5 Centigrade. if we replace the lm35 on the same hardware it starts working fine again with correct values.
 

If you are using a plastic package LM35, it may be a problem of moisture or even acid fume having penetrated the non-hermetic package. Only a metal can package can be considered long term reliable under condensating or agressive athmosphere conditions.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top