cn-0209

Hi,

      I need to design a universal analog input module .I have referred to CN-0209.But I could not understand the purpose of ADG442 used in the circuit.Can I get help?

Regards,

Divya

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  • 0
    •  Analog Employees 
    on Mar 5, 2014 8:50 PM

    Hi Divya,

    The front end will only sample one channel at a time. The procedure would be as follows:

    1. Sample channel 1
      1. Close S5, S7 of ADG1414, all other switches open
      2. Allow input to settle
      3. Measure input channel
    2. Sample channel 2
      1. Close S6, S6 of ADG1414, all other switches open
      2. Allow input to settle
      3. Measure input channel
    3. Repeat

    If both channels were thermocouple, the procedure would be similar, though you'd be using he ADG442 switches instead.

    If Channel1 was ±10V and Channel2 a thermocouple, then it would be possible to leave Channel 1 connected to the AD8676 and Channel2 connected directly to the AD7193. Then use the AD7193's internal Mux to switch between them.

    To support 4-channels there are two options:

    1. Add another copy of the ADG1414 circuitry (including AD8617); note that the voltage input for this can go to the same AD8676 as already present in the circuit. Also Add another ADG442 switch for the thermocouple/RTD; I would switch all the thermocouple RTD's to AIN1 and AIN2. The reason for this is that you can then add another 2 current inputs and connect the 200ohm resistors to AIN5 and AIN6 respectively.
    2. You could double up the entire circuit (including ADC). The advantage of this is that the sample rate per channel will not decrease over the two channel version; the more channels you add into the ADC, the slower your effective sampling rate as you need to switch+settle between more channels.

    Regards,

    Derrick

Reply
  • 0
    •  Analog Employees 
    on Mar 5, 2014 8:50 PM

    Hi Divya,

    The front end will only sample one channel at a time. The procedure would be as follows:

    1. Sample channel 1
      1. Close S5, S7 of ADG1414, all other switches open
      2. Allow input to settle
      3. Measure input channel
    2. Sample channel 2
      1. Close S6, S6 of ADG1414, all other switches open
      2. Allow input to settle
      3. Measure input channel
    3. Repeat

    If both channels were thermocouple, the procedure would be similar, though you'd be using he ADG442 switches instead.

    If Channel1 was ±10V and Channel2 a thermocouple, then it would be possible to leave Channel 1 connected to the AD8676 and Channel2 connected directly to the AD7193. Then use the AD7193's internal Mux to switch between them.

    To support 4-channels there are two options:

    1. Add another copy of the ADG1414 circuitry (including AD8617); note that the voltage input for this can go to the same AD8676 as already present in the circuit. Also Add another ADG442 switch for the thermocouple/RTD; I would switch all the thermocouple RTD's to AIN1 and AIN2. The reason for this is that you can then add another 2 current inputs and connect the 200ohm resistors to AIN5 and AIN6 respectively.
    2. You could double up the entire circuit (including ADC). The advantage of this is that the sample rate per channel will not decrease over the two channel version; the more channels you add into the ADC, the slower your effective sampling rate as you need to switch+settle between more channels.

    Regards,

    Derrick

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