Low-Power RTD Temperature measurement

[Walx]

Hello!

I need a circuit-idea (analog-part) for measuring the Temperatur
with ATMega88 + MCP6044 OP's + NI1000 (i have to use this ones)

The Problem is, that the whole circuit must not consume more than
800µA, and the accuracy should be +/- 0,5°C!!!

Now the circuit draws about 900µA (Average).
CPU-Active: ~ 150µA
LCD+SPI: ~ 150µA
ANALOG+ADC: ~ 500µA

 

[VVV]

The usual solution is to switch on and off the RTD. Turn is on just while you are doing the conversion, then turn is off.
That way, the AVERAGE current consumed by the circuit will be reduced, depending on how often you need to make the measurement.

 

[bobcat1]

HI

Lower the cpu clock - this method might save you some current



All the best

Bobi

 

[Walx]

HI

Lower the cpu clock - this method might save you some current



All the best

Bobi

Thanks, but i already use the internal RC-Oscillator with divider
8MHz/256 -> 125kHz, then i calibrate this value by using the 32,786kHz
crystal to 115,2kHz, to get exact baudrates. (I only need 300-2400Baud)

As you can see in my first posting, the external analog circuit draws most of
the current!

So im looking for a analog-circuit for measuring a NI1000-sensor and the resistor-rotation-switch circuit with lowest power consumption.

May i need a currensource (let's say 10µA ...).

I'm not so confident with analog-circuits, so i ask you guys!

 

[VVV]

Why don't you try what I suggested in the previous post: switch on the RTD only while you measure it, and keep it off the rest of the time.

Using low currents for measuring RTD's is not a good idea, since the voltages developped across the RTD will be very low and you lose resolution due to noise.