INA330: INA330: Is Rset relative position to Rtherm important?

Hi Mike,

The voltage applied to the INA330, A2 non-inverting input in datasheet Fig. 5 establishes the voltage that is applied across Rtherm. The current I1 through Rtherm, tracks any change in the Rtherm (~10 k) resistance value. Any resistance added in series with Rtherm will be seen as an error term.

Two feet of copper wire of any reasonable gauge will add only tens or hundreds of milliohms in series with Rtherm. That represents millipercents of error resistance, of the total resistance. The wire resistance should be relatively fixed at room temperature for a given length and gauge. However, it will have a specific temperature coefficient so its resistance will change with temperature. Again, the overall wire resistance change won't be much compared to the changes that occur in Rtherm with temperature.

One issue may have not given thought to is EMI-RFI picked up by the Rtherm 2' connecting wires. It is suggested that twisted pair, or shielded cable be used for the connection between the thermistor and the INA330 inputs. If you suspect that EMI-RFI might be an important consideration, an X2Y capacitor should be used at the INA330 inputs. Additionally, correctly selected ferrite beads should be placed over the input cable. This forms a common-mode transformer that is effective in attenuating RF common-mode currents.

Regards, Thomas
Precision Amplifiers Applications Engineering