# Electronic Circuits and Projects Forum

1. ## pt100/pt1000 as temp sensor

Hi.
I am thinking of using pt100/pt1000 as temperature sensors in designing an anemometer. the two sensors must be heated equally and one shieled from the other, air blown over one should affect the bridge balance and give a voltage output related to the speed of air..... i then need to use an ADC and AVR to display the results.

can any1 suggest any circuit arrangement for the above and any suggestions plz...........

2. Go back and give this thread a read. There were some good ideas shared in the thread and suggestions as well. I would start with the basics before I worry about an AVR.

Ron

3. Make circuit that drives the temperature dependent resistor with constant current. Then measure the voltage across the resistor. The voltage is proportional to wind speed.
Other option is to apply constant voltage over the temperature dependent resistor and measure the current through it.. which should be proportional to wind speed.

4. PT100 and PT1000 have a positive temperature coefficient.

Cooling one in the air flow means decreasing resistance. How do you calculate the inverse voltage drop into wind speed directly?

You can't use the uncooled temperature sensor since it's resistance depends on ambient air temperature.

Here is a circuit using two transistors as sensors (much cheaper than PT100s).

Boncuk

5. ## pt100/pt1000

hi,

i have tried the thermistor circuit it dint work well.. as one thermistor was heated and another was at room temp... so i was thinking of heating both the sensors and subjecting only 1 to air flow.. i was thinking about using 2 1k thermistors in a wheatstone's bridge with 1k resistors and then amplifying using an opamp....
i am confused as to use constant current or constant voltage and which one will work best for my application?

any circuits/ideas plz help...............

6. I would start by giving thought to the circuit that Boncuk presented. Using thermistors and bridges just gets into more to worry about. Try with a simple focus on using transistors like a 2N3904 for starters. I am sure a Google of Temperature Measurement with 2N3904 will bring a bunch of hits. Get familiar with using a low constant current source through a pair of transistors and measuring the subsequent voltage drops across each. Anyway, I never did it but how I would likely look to do it. Then comes a means to calibrate it and get it accurate. Anyway, I liked Boncuk's suggestion.

Ron

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