Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 46 subscribers
  • Views 771 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS1148: ADS1148

Stanislav Dimitrov
Prodigy 60 points
Part Number: ADS1148
Other Parts Discussed in Thread: ADS1243, ADS1241, ADS1242, ADS1248, ADS1240,

Dear All,

I am planning to use ADS1148IPW for Pirani vacuum gauge sensor.

Schematic is as below:

However, looking at the calculations, it requires REF voltage of 200 mV. 

Is it possible to use 200 mV directly as suggested or this will affect the resolution? If I use 2.047 V for example, and use the gain, how to divide it so no temp drift, etc. present errors. The filament of the Pirani sensor is also about 4 Ohms, and the current through it is 0,4 A.. Any help as suggestions and opinions is more appreciated. 

Best Regards,

Stanislav

  • 0 in reply to Stanislav Dimitrov
    TI__Guru 50541 points

    Hi Stanislav,

    Can you share the part number for the Pirani gauge? 

    The ADS1248 reference cannot go that low, however the ADS1240, ADS1241, ADS1242, or ADS1243 may be a candidate as it's reference can be a lower magnitude, 100mV to 5V. 

    Let me check with some other members of the team to see if there are any other devices that may be more suitable for your application. 

  • 0 in reply to Alexander Smith
    Prodigy 60 points

    Dear Alex,

    Thank you for stepping in about this. 

    The gauge is an old one produced in Chechoslovakia, it is only one line with 4 Ohm wolfram wire inside and 3.5 Ohm copper wire wrapped around the base of the gauge. Additionally, two potentiometers are added, all forming Wheatstone bridge. Currently, the schematic is realized with a lot of opamps and we want to upgrade it because the electronic elements started to degrade and the installation cannot work as stable as expected.

  • 0 in reply to Stanislav Dimitrov
    TI__Guru 50541 points

    Hi Stanislav,

    My pleasure. To be honest with you, I am not very familiar with this type of application, but I will do my best to assist. 

    I see. What started to degrade? In my experience, capacitors are typically the first components to degrade. 

    Did you take a look at the ADS1240/1/2/3? The team was not aware of any other devices we have that support reference voltage below ~500mV. 

    If you use the ADS1148 with a reference voltage of 2V, the current will need to be limited through the filament, perhaps with an additional resistor, or the bridge circuit may need to be modified in order to limit the current. The second challenge will be that the output signal from the bridge circuit will be low in magnitude. If it's 200mV, then only 10% of the full-scale range of the ADC will be used. 

  • 0 in reply to Alexander Smith
    Prodigy 60 points

    Thanks a lot. I will use ADS1240.