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4 to 20 mA Analog input 16 bit ADC with SPI interface

Liu Yang
Expert 6035 points
Other Parts Discussed in Thread: RCV420, ADS114S06, INA214

Hi Team,

One of my customer are searching for a part having the features that 16bit, 4 to 20mA anlaog input with Bus voltage of 24V support, SPI interface, single channel ADC. Our application is to interface with HS 420 vibration sensor and collect the digital data through SPI interface. Please support us to find the same part.

It is simple to select ADCs using Resolution(Bits), interface and number of input channels at TI's web page, but I do not know how to select using "4 to 20mA anlaog input with Bus voltage of 24V support". Could you give me some advice?


Beat Regards,
Tom Liu

  • 0
    TI__Guru**** 174266 points

    Hi Tom,

    At the moment, we do not have any ADC's which directly interface to a 4-20 transmitter.  You would need to convert the current to voltage and then apply that to the ADC.  Take a look at the RCV420 as a possible means to do the current conversion.  How many ADC channels are you looking for?

  • 0 in reply to Tom Hendrick
    TI__Mastermind 41781 points

    Hi Tom L,

    In addition to Tom H's feedback, we see many customers just using a shunt resistor to convert the current to voltage. Generally this is a 250 ohm shunt, but it can be whatever value you determine is best for your system. Many ADCs include a 2.5V reference, so using a 100 ohm shunt makes sense in this case, as the max voltage is 2.4 V (100 ohm x 24 mA). One such example of this type of ADC is ADS114S06, which is a 16-bit, 4kSPS, 3-diff channel ADC with an integrated precision 2.5V reference. I have drawn a simple block diagram below

    • It would be helpful to know how fast you need to sample the 4-20mA signal
    • Also, will the system be powered by the loop, or will the 4-20mA transmitter have its own power source? In other words, will you have a 2/3/4-wire transmitter?

    Please let us know so we can make sure we have identified the correct ADC for your application.

    -Bryan

  • 0 in reply to Bryan Lizon86
    TI__Expert 6035 points

    Hi Bryan,

    Our Expected sampling rate of the ADC is 10 to 20ksps.

    Our application is sensing the vibration rate using HS-420 vibration sensor that have 3 wire, Here I am attaching the datasheet of the HS-420 vibration sensor kindly go through the same. We need to give a 24V supply to the same sensor from the board and sense 4-20mA current variation through the ADC. If ADC have the option to give 24V supply to the sensor that will be good for us. Hope this information's are enough to clear your query's.

    HS 420 2 PIN CONNECTOR.pdf

    Beat Regards,
    Tom Liu

  • 0 in reply to Tom Hendrick
    TI__Expert 6035 points

    Hi Tom,

    Our ADC is single channel. We have a concern about the part (RCV420). We need 12 nos with the same part in a single board. So can u suggest any other low cost current to voltage converter for this same application?.
    Or else can we use INA214 for the same application? if we can use the same, can you share the part number of 0.5% gain error ie version C part.

    Beat Regards,
    Tom Liu

  • 0 in reply to Liu Yang
    TI__Guru**** 174266 points

    Hi Tom,

    Do you already have an ADC picked out?  You could use one of the INA devices here - the 0.5% gain error part numbers are listed in the back of the datasheet starting on page 29.  You would be looking for INA214Cxxxx for example, depending on the package you intend to use.