INA326: TINA TI convergence problem

Hi Vidhya,

Thanks for your post. Can you please attach your TINA file? I'd like to open it and take a closer look at the issue here. 

Hello Tamara,

Refer to the circuit below.

Kindly revert.ADC sim.TSC

Thanks,

Vidhya

Hi Vidhya,

you set the gain of INA326 to 2 x 160k / 2k = 160,

but at the same time you heavily overdrive the input if INA326:

This cannot work.

Why is R4 so high??

Kai

Hello Kai,

I tried to add noise filters. 

Do we need to add the noise filters - R4,R5, C6,C7 and C8 as highlighted below? How to decide those values?

Please suggest. 

Also share the working .tsc

Thanks and Regards,

Vidhya

Hi Vidhya,

if this was the plan, then you have omitted the second 10k resistor and you have erroneously mounted the 10k resistor within the 100µA constant current path.

Yes, using the input filter is mandatory when handling very small signals and if they come from the outer world.

Kai

Hi Kai,

How to calculate the filter values? 

I tried to simulate now without input filters, but output 5734.ADC sim.TSCshows <10mV range instead of 2.9V for which the gain is set.

RTD=177.23Ohm, Expected output is 2.91V but the value read is 6.08mV.

VM3 voltage is as expected- 17.72mV.

PFA .tsc file.

Kindly share your thoughts.

Thanks,

Vidhya

vidhya_ina326_1.TSC

Kai

Thanks Kai,

But VF1 has reached 603.91mV for 177 Ohms.

The gain is set to 160 to reach this VF1 to 2.84V (for a 3V full scale)

Why is the VF1 read as 603mV?

KIndly clarify.

Thanks,

Vidhya

Hi Vidhya,

100µ x ((177 +10) - (78.7 +10)) x 160k / 2k x 2 x V = 1.57V which exactly equals the voltage at the measuring point VP_8. So the circuit is working well.

Kai

Thanks Kai.

Gain is set to 160. So vout at 177 ohm is expected to be 2.9V. But simulation shows 1.57V

Please clarify how to overcome this offset.

Regards,

Vidhya