7 Replies Latest reply: Aug 3, 2014 9:09 AM by Ehsanavr RSS

    CN0267 + AD5700D2Z to measure 4-20mA


      Any recommendations to adapt AD5700D2Z to measure 4-20mA produced by "legacy" field industrial instruments in plants?


      In CN0267, we can see how to measure TC and Bridges but 4-20mA? How about 0-5VDC?



        • 1. Re: CN0267 + AD5700D2Z to measure 4-20mA

          Hi there,


          Can I just clarify that you are still talking about a loop-powered field instrument design, except instead of a pressure sensor input, you want to measure a 4-20mA input or 0-5V input, correct?


          • 2. Re: CN0267 + AD5700D2Z to measure 4-20mA

            Thanks tjohnson,


            Exactly, it happens there are in the industrial environment tons if not millions of chemical transducers in water treatment without "HARTability".  Those transducers -disolved oxygen, pH, conductivity- actually report 4-20mA (or 1-5VDC using a 250ohms shunt)...


            Thanks again.  Your answer is very important.

            • 3. Re: CN0267 + AD5700D2Z to measure 4-20mA

              Hi there,


              The Analog input signal can be connected via any standard 2.54mm pitch connector soldered on the CN0267 board. The demo, as shipped, accepts a differential signal of 0 to 160mV, typical, connected between AIN+ and AIN– inputs. This differential signal is biased to a common mode voltage of approximately 1.65V (half of  3.3V AVdd).


              The differential analog input signal is measured ratio-metrically with respect to a differential reference voltage connected between REF+ and REF– inputs.  A 3.3V AVdd power supply is also available on the input connection, as well as a signal connecting the sensor to ground via the ADuCM360 ground switch. Note that the ground switch is activated from the firmware.


              So, in your case, once the transducer output can be divided down to suit the input range of the ADC => CN0267 can be adapted to suit your needs.


              Analog Input Test Circuit:


              Best Regards,


              • 4. Re: CN0267 + AD5700D2Z to measure 4-20mA

                Hi Carlos,

                One thing that te reason the input on the CN0267 is 0-160mV as standard is because the PGA gain is set to 8. The ADuCM360 could be reprogrammed with PGA gain=1 to allow a ±1.2V input range, an external reference could increase this range also. The c-code can be found at this link.

                This link is for the user guide for downloading code to the ADuCM360 evaluation board, the steps are identical for the CN0267 board. One thing to note is that to download the new code to the ADuCM360 you will need the ADuCM360 evalaution board (EVAL-ADUCM360QSPZ), as this contains the J-Link OB emulator which provides nonintrusive emulation via a serial wire, and also provides UART communication with the ADuCM360 from a PC.



                • 5. Re: CN0267 + AD5700D2Z to measure 4-20mA

                  Thanks Derrick, it was going my next question about PGA gain.  I was looking at the C-Source code a few days and I remember something like that.


                  The source says, right?


                  // --------------------------------------------------------------------------

                    // ADC 0

                    // --------------------------------------------------------------------------

                    // Measures primary sensor input voltage

                    // Input buffered, AIN0, via RC filter from connector J5 pin 3

                    // Input buffered, AIN1, via RC filter from connector J5 pin 4


                  // For default demo:

                    // Gain = 1

                    // Vref = AVdd (unbuffered)


                    // For demo with pressure sensor (#define PressureSensor in "AFE.h")

                    // Gain = 8

                    // Vref ext. (unbuffered), VREF+ connector J5 pin 2, VREF- connector J5 pin 5


                    // Conversion continuous, chopping, filter sin3 50Hz with extra 60Hz notch

                    // Result every 60ms


                  Removing comments, Vref = AVVdd = 3.3V???  It means the AIN0/AIN1 tolerates higher voltages, right?


                  Yes, I am checking about the PGA Gain because I read it may affect the power consumption and it is supposed the 5700 Demoboard is powered loop, right?


                  My idea was to buy the boards (your recommendation for the EVAL-ADUCM360QSPZ is great) and start testings with different gains.


                  Thanks again, it was very helpful.


                  Carlos A. Estrada

                  • 6. Re: CN0267 + AD5700D2Z to measure 4-20mA

                    Hi Carlos,


                    An analog input pin can have a voltage of AVdd applied to it but, the differential max voltage that the ADC can measure is lower than this and is PGA dependent (e.g. datasheet tables 2 and 3 outline the input ranges). The absolute max ratings for the device are specified in datasheet table 14, for Analog Inputs to AGND, the absolute max rating is: −0.3 V to +3.96 V.


                    The power consumptions for the different PGA gains are listed in the specifications (table 1), the values are listed below (typ. values):



                    My pleasure, glad I could help.



                    • 7. Re: CN0267 + AD5700D2Z to measure 4-20mA

                      Hi Derrick

                      i have a problem in my project that i used ADU360M IC.

                      i have a strange problem because there is no any answer for me.

                      i used CN0267 circuit note and designed PCB myself.

                      after that i completed all the component on the board then connected J-LINK programmer in it.

                      programming was succeed but ADU360 didnt work.

                      when i started Debug from Keil_uvision, ADU360 work successfully but if i restarted the board or connect and disconnect the power supply microcontroller doesn't work again.

                      this means that my board work when just connected the debugger in it when i disconnect from debug in this way Still working continues

                      i was confused  for this problem.

                      The schematic of my project:


                      please help me.