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ADS131E08 Interface with a PT

Aditya Ayachit1
Prodigy 50 points
Other Parts Discussed in Thread: ADS131E08, MSP430F2619

Hi TI Team,

We are in the process of development of a Circuit which measures AC Voltage and AC Current using MSP430F2619 and ADS131E08.

We have been able to interface with SPI very successfully and the bruises on ourforheads will heal soon.

We are able to measure MVDD correctly.

We are using a single Supply scheme. The Reference Voltage is 4V.  OMPAMPOUT = 2.54V

We are interfacing this circuit with a Potential Transformer and have implemented the circuit shown on Pg. 49 Figure 51b.

Following are the values of the components:

R1 = 330K  

R2 = 3.3K

R3 = 10K

RF= 470pF

The figure shows that there is no connection to the neutral. We have also left our neutral open. If we connect it to the AGnd, the transformer heats up. If we leave it open and measure the resultant voltage from the PT, then when the voltage is 8V AC the result is 0.015 Volts!

In the final installation the PT will have the ratio of 800/100, which should explain the selection of R1 and R2 values.

I am sure that the fault is in my understanding of the circuit. Could you please also guide me to some good resource along with your explanation.

Kind Regards,

Aditya

 

But when we connect the circuit to 

  • 0
    Prodigy 50 points
    Correction....
    Rf = 2K2
    C = 470pF
  • 0
    TI__Mastermind 23235 points

    Hello Aditya -

    If you are using a PT, is there a reason that you don't use both sides as shown in Figure 51a?  Differential measurements provide much better immunity to noise and therefore give you better measurements.

    For reference, you might want to check out some of the reference designs on the Smart Grid portion of the site; the link to the electricity meter portion is shown below

    http://www.ti.com/solution/docs/appsolution.tsp?appId=407

  • 0 in reply to Greg Hupp
    Prodigy 50 points

    Dear Greg,

    Thanks for your inputs. I am happy to inform you that right now I am getting correct Voltage readings. Now we will move on to the CT Readings.

    We have got the correct readings when we connected the Neutral line to IN1N along with the offset voltage. There is no heating of the transformer or for that matter of the ADS IC also.

    We totally agree with you that we should use a dual power supply which will increase the noise immunity. We will undertake the iteration of the design and implement the suggestion by you.

    We also want to thank you and your team for developing such a fantastic IC! We will sure be using the AFE's from you more often. The power up sequencing flowchart is a lifesaver. Only one request please make the datasheets more user friendly. 

    Kind Regards,

    Aditya Ayachit

  • 0 in reply to Aditya Ayachit1
    TI__Mastermind 23235 points
    Hello Aditya -
    I am glad we were able to help. Please let us know if there is anything further that we can help you with.
    Additionally, any suggestions you have are always welcome and appreciated so that we may continue to improve the information we provide to our customers.