INA188: Regarding: Not getting expected output at INA188 signal conditioner

Ankeet Gugale

Part Number: INA188
Other Parts Discussed in Thread: TIPD209, XTR117, , OPA2317, XTR111, XTR116

Hello All,

I have designed a custom board( Resistivity sensor) using the reference design (TIPD209_Hardware_E2.SchDoc). I have replicated the design as it is.At present, the input to the wheatstone bridge is a 10K potentiometer. The output of the INA188 is given to XTR117(voltage to current transmitter). I am not getting the expected output at the INA188 output pin. I am getting the variable output in the range of 7 Volts to 10 Volts(which is not sufficient).

I request you to please review the design and give the feedback on the same.

Please find the attached schematic and layout pdf.

Thanks in advance

Ankeet Gugale

sensor_pcb-0.9.0.pdf sensor_sch-0.9.0.pdf tidrl23.pdf

over 5 years ago

0 Tamara M Alani over 5 years ago

TI__Genius 10850 points

Hi Ankeet,

At first glance, I see that the INA188 in TIPD209 is powered off of 24V whereas yours is 12V.

What is your expected input voltage to the INA188?

-Tamara

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Ankeet,

should work:

ankeet.TSC

I'm not clear what you want to do with this 10k pot. A PT100 has about 100R and a thermocouple cannot be modelled by a simple 10k pot. A thermocouple is a voltage source.

Kai

0 Ankeet Gugale over 5 years ago in reply to Tamara M Alani

Prodigy 155 points

Hi Tamara,

Thank you for replying.

I forgot to mention. I am giving 24V input votage to INA188.

Please verify and confirm

Thanks and regards

Ankeet Gugale

0 kai klaas69 over 5 years ago in reply to Ankeet Gugale

Guru 140200 points

Hi Ankeet,

please explain what you are doing with the 10k pot.

Kai

0 Ankeet Gugale over 5 years ago in reply to kai klaas69

Prodigy 155 points

Hi Kai,

Sorry for replying late.

The 10k pot is used as a replacement(for testing purpose only) for water conductivity sensor. Later i am going to replace the pot with conductivity sensor.

0 kai klaas69 over 5 years ago in reply to Ankeet Gugale

Guru 140200 points

Hi Ankeet,

where is the 10k pot connected to in your schematic? At J2 or J3?

Kai

0 Ankeet Gugale over 5 years ago in reply to kai klaas69

Prodigy 155 points

Hi Kai,

The 10K pot is connected to J1,

Please find the attached schematic. the previous schematic was mirrored. Sorry for the inconvenience.

regards

Ankeet

0 Ankeet Gugale over 5 years ago in reply to kai klaas69

Prodigy 155 points

Hi Kai,

The 10K pot is connected to J1. Please find the attached schematic. Previous schematic was mirrored. Sorry for the inconvenience.

Regards

Ankeet3324.sensor_sch-0.9.0.pdf

0 kai klaas69 over 5 years ago in reply to Ankeet Gugale

Guru 140200 points

Hi Ankeet,

there are several issues in your circuit:

1. You have driven the output of OPA2317 into saturation. See the output voltage specification on page 2 of datasheet of OPA2317.

2. The bridge must be very well balanced, if you choose such a high gain at the INA188. Reduce the gain and keep the bridge balanced.

3. The XTR117 doesn't work like that. If you want to drive the input of XTR117 by an external signal, you will need to provide optical isolation. We have discussed this issue several times here in this forum. Search for "XTR116" and "XTR117". Another remedy is to use a true voltage to current converter like the XTR111, or similar, instead of the XTR117 which is a loop powered 4...20mA current loop transmitter.

Kai

0 Ankeet Gugale over 4 years ago in reply to kai klaas69

Prodigy 155 points

Hi Kai,

Thank you for the feedback. I will do the above mentioned things and get back to you shortly, if any queries

0 kai klaas69 over 4 years ago in reply to Ankeet Gugale

Guru 140200 points

Good luck!

Kai

0 Tamara M Alani over 4 years ago in reply to kai klaas69

TI__Genius 10850 points

I hope this resolves the issue. I am closing this thread. You may reply to re-open if you have more questions regarding this topic.

-Tamara

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INA188: Regarding: Not getting expected output at INA188 signal conditioner