6 Replies Latest reply: Nov 14, 2011 1:02 PM by Cman RSS

    CN0209: Universal AFE questions


      1- How would I do the same circuit for 8 channels (CN0209 is for 2 channels), and with minimal components? (RTD 2-3 wires (no 4 wires), TC, 4-20mA)


      2- What is the configuration of the ADG1414 for each measurement mode?


      3- What is the correct connection for TC (figure 2)? The connection is JX-3, JX-3 ???????


      Thanks a lot.

        • 1. Re: CN0209: Universal AFE questions

          Hello Javier


          For your question 1. The  robustness trade-off with cost (i.e. components), therefore for minimum components! you need to factor this in.

          There are numerous way in resolving your design. This would required more than just a few thread in EZ. We need to take this off-line, Where we can get more info, in order to propose some architectures for your consideration. Things that need to be consider is your requirement and specifications in order to implement the architecture. You can contact me by email thru CAC Europe. I believe you may also have my answers to (Q3) thru our ADI representative. If not please see (3) below for your answer. For (Q2) the query was too brief, can you elaborate, again you can reply to my answer thru the CAC Europe  (SR#: 1134516).


          Answer to question 3:


          => There is a typo in fig2.
          (i) wrt TC (Thermocouple) i.e. in the sub diagram/box, It should ideally read (from left to right) as Jx-1, Jx-2, Jx-3, Jx-4. Where the x is either 'ALL' channel one i.e. (1). Or, x is either 'ALL' channel two i.e. (2). Hence you can in effect have up-to two TC (one per channel). This should clear up everything. I have cc the circuit note (CN)  team leader, where they will factor this notification for the next doc revision/update, please accept our apologies.


          Further to this TC connection, below is my decoding of the CN schematics for the  TC (thermocouple) path/configuration to the ADC
          This is best describe and refer in-conjunction with the full schematics by means of tracing the signal path to the ADC, see the circuit note (CN0209)companion documentation, EVAL-CN0209-SDPZ-SCH- RevB.pdf.


          For TC (in fig 2), For each channel this can be connected to the ADC thru the ADG switches. Note, this can be (a) either (b) or both, be connect thru the switch (ADG1414/ADG442)!. For control, please see each respective ADG datasheet for more detail.


          IF say your connection is thru ADG1414 you need to program these switches. Again this can be refer to the companion schematics (isolator switch, blackfin SDP) and the software.


          If it's configured appropriately (all the way to and including) the ADC (AD7193). Then the input to the ADC i.e. => AIN3 (is singled-end), while (thru ADG442) the ADC port (AIN1 + AIN2), (AIN5 + AIN6) are differential.


          Hope this helps, in which way and what ends up to the ADC.





          • 2. Re: CN0209: Universal AFE questions

            Hello Ching, first of all, thaks for your answer. I don´t know how to answer thru CAC Europe.


            Attempt to better explain the doubts I have about the circuit:
            1-  "with minimal components" I refer to the minimum possible connections through switches, to make a universal input (3 vias connector), suitable for TC, RTD, 4-20mA, V, measurement. I want to use the same 3 vias connector for the input sensor (x8 channels). The CN-0209 use a 4 vias connector for RTD, TC ... y 2 vias for 4-20mA.
            2- "What is the configuration of the ADG1414 for each measurement mode?" I want to know the internal switch state in the ADG1414. For example:
                 - RTD Measurement mode: S1-S2, S3-S4 closed, S5-S6-S7-S8, open. (internal switches of ADG1414).
                 - TC Measurement mode: xxxxxx
                 - Voltage Measurement mode: xxxxx
            I can configure each channel of AD7193 independently? Channel 1 for RTD (differential) and Channel 2 for 4-20mA (unipolar)...
            3- The TC connection is.....?
                 Jx-1: no connect
                 Jx-2: TC
                 Jx-3: TC
                 Jx-4: no connect
            Best regards.
            • 3. Re: CN0209: Universal AFE questions

              Hi  Javier


              (1) I presume your 3 vias, is the connector header pins you are talking about. If this is correct then several scenario exists (a) do you want to maintain consistency as the CN' design but with 8 channels, than the current 2. (b) use one ADC as its 8 channels (but this restricted to single end-ed. (c)  a mix and match.


              For (a) it’s the simplest, hence i.e. is just some duplication of the switches and 3 extra adc. Advantages can have 4 simultaneous ADC running.

              For (b) need some thinking if do-able for one  x 8 channel ADC. you need to provide more feedback info for requirements. see below

              For (c) needs more feedback info for requirements . see below.


              Can you advise which preference (i.e. single end-ed, differential) and what's do-able in meeting your requirements.


              for (2) is easier to answer with a phone call. Please provided.

              for (3) i thought this was answered previously. else please elaborate. Hence it's Jx-2: and  Jx-3:


              Can you let us know if you have the EVAL-CN0209-SDPZ, where you can do some initial evaluation for your requirement specification.




              • 4. Re: CN0209: Universal AFE questions

                Hi Ching.


                First of all, the initial requeriments of my project:


                     - 8 universal analog inputs (RTD, TC, 4-20, Voltage). 3 header pins.

                     - Each channel can be configurated independently for RTD, TC ... measurement mode. Another choice if this option complicates the design (cost &      component number (PCB size)), 2 blocks (4+4 inputs) and can configurated each block for each measurement mode.

                     - The sample rate is not a critical factor.

                     - This is controlled for a 32 bits ARM Cortex kinetis, communications Ethernet, CAN and RS-485. It´ll be a web based application.


                     I´ll configure each analog input (with switches and analog multiplexers, jumpers no allowed), with a software through communications, and monitoring         too.

                (1) The inputs must be differential.  I've thought about putting 2 ADCS (1 for each block).
                (2) Sorry, i want give you the phone number, but i don´t speak English.

                     I attempt to explain how the circuit works (CN-0209),  and if I'm wrong tell me.
                     mA input: single ended, through AIN4, AIN8.
                     Voltage input: Single ended, closed the switches of ADG1414, tied to AD8676-AD8275-AIN3
                     TC input: Differential, through ADG442-(AIN1-AIN2)&(AIN5-AIN6). AD8617 is used in the path of thermocouple circuit?? is my doubt.
                     RTD input: Differential, through ADG442-(AIN1-AIN2)&(AIN5-AIN6). AD8617 is used for current source.
                (3) Solved.
                I don´t have the EVAL-CN0209-SDPZ, i am doing my own prototipe board.
                • 5. Re: CN0209: Universal AFE questions

                  Another question:


                  How the third wire RTD is compensated? The circuit does not connect the wire to the analog input....


                  What would be the equation to calculate the resistance?


                  Thanks again, Ching.



                  • 6. Re: CN0209: Universal AFE questions

                    Hi  Javier


                    I think to support you better.


                    (a) Can you get hold/purchase one of the eval-board for testing and evaluation.

                    (b) Have a look at the attached files

                    (c) To support you further, do you know of any ADI representative or ADI (authorised) distributer (FAE) in your area. where they can assist and liaison with. As thru EZ would be difficult to go thru all the scenarios if you are not familar with the CN designs.