Configuration for universal analog input in AD7124_8

Hi,

!)I want to use AD7124_8 for universal analog input. So that I can connect channel number RTD or TC or 4-20mA or 0-10V.Is that possible with Ad7124_8?

2) AD7124 ADC 8 channel differential input is there so that can use channel one for RTD  application, Channel two for Thermocouple application,channel three for 4-20mA application, and channel four 0-10v application. So is that possible to configure like this way in AD7124_8?

Parents
  • 0
    •  Analog Employees 
    on Aug 28, 2020 4:18 AM

    Hi,

    I believe yes it will definitely possible. Especially the RTD and TC inputs as most of the building blocks needed for this type of sensors are already integrated on the chip. We have a reference circuit that will help you start with the design of TC with RTD as its cold junction. Please see below reference circuit.

     https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0384.pdf

    For the 4-20mA and 0-10V inputs, this will require an external shunt for the current input and attenuator divider for the voltage input.

    We also have available AD411x family that will also suit your application.

    AD4111/AD4112 are capable of measuring direct 0 to 10V and 4-20mA inputs without the need of any external circuitry. You can use this along with AD7124-4 for your universal input module.

    We also have AD4110-1 that allows all inputs above in a single ADC. However, if you require 4 channels I think an external Mux will be needed here.

    Please see also all available resources that you may find helpful.

    https://www.analog.com/en/applications/markets/industrial-automation-technology-pavilion-home/plc-dcs.html 

    Thanks,

    Jellenie

  • 0
    •  Analog Employees 
    on Aug 28, 2020 6:29 AM in reply to JellenieR

    Also, you can take a look at the CN0414 reference design.

    Regards,
    Mihai

  • 0
    •  Analog Employees 
    on Sep 1, 2020 7:03 AM in reply to heatcn

    Hi,

    1. Actually you can use other CJC other than RTD, but the same RTD circuit and configuration can be use for your RTD sensor even if using this as CJC or for any other temperature measurements. So you can use two RTDs with different functions or other sensor for CJC.

    2. Can you clarify what specific issues are you encountering with respect to shunt resistor?

    3. I would say both parts performed very well at a reasonable cost and with respect to their target application and system requirements. I wouldn't disagree if you have selected AD7124 as this can be suitable for your application but will require some external components to accommodate all your needs.

    4. Can you clarify what it means by 16 channels, does it mean each channel of 16 channels can accommodate any of the RTD, TC, current and voltage measurements? If yes then it would probably required external switches and muxes. Could you check this thread and see if this is something similar to what do you need to do? Do you have any specific target volume for this production?

    https://ez.analog.com/data_converters/precision_adcs/f/q-a/163997/multiple-channels-with-ad4110-1/371491#371491 

    5. I believe Mihai mentioned that the code will be available soon. But we also have other sample codes that you may find helpful.  

    https://wiki.analog.com/resources/tools-software/product-support-software/sigma-delta_adc_temperature-ble_demo?rev=1591600357

    https://wiki.analog.com/resources/tools-software/product-support-software/ad7124-stm32

  • Hi,

    1 ) The EVAL-AD7124-8-PMDZ  board is good.but my problem that how to configure universal analog input schismatic to this board. especially if I want first channel all input like rtd,4-20mA,0-10v, and Tc.

    2)  What is the difference between AD4112 and the AD4111 part number? only price?.

  • 0
    •  Analog Employees 
    on Sep 2, 2020 1:35 PM in reply to heatcn

    Hi,

    1. The configuration needs to be done in software. Please check out the datasheet. You can have up to 8 different setups and you can connect any analog input to any channel.

    2. AD4111 has the unique feature of open-wire detection on the voltage inputs while AD4112 doesn't. This is why AD4112 is cheaper.

    I would recommend using AD7124-8 for rtd and Tc and AD4112 for 4-20mA and 0-10V inputs. Is this way you reduce the number of external necessary components.

  • 1) if I use other CJC, then the accuracy compare to RTD is less. If I need to measure thermocouple then I want to use one cjc.there am using rtd as a cjc. so is the same rtd sensor I can measure to temperature measurement (-200 to 400 degree)?.so that I can save an extra rtd sensor configuration.

    2)4-20 mA input am converting to voltage using shunt resistor(250 E/470E)So that i will get some voltage with respect mA.this volage am using for my calculations. but this issue happens is if some other 4-20mA sensor then my circuit will get slow to measure the readings it looks like delay.some time my circuit will get hanging.

    3) if I use external mux then how I configure this universal AFE to AD7124. Mux if I added to my circuit I think sensor response time will reduce.

    4) For you, a better understanding is attaching the block diagram of our current datalogger instruments.

    PDF

    This above pdf you can see U6 &U7 this is the mux. here and using these two mux for 16 channel measurements.U6 mux is dedicated to rtd application and U&7 for mA application.so that here 1- 8 channel I can measure rtd and 8-16 channel I can measure 4-20mA reading.

    what I need that I need to measure all universal analog input. It may be rtd or mAor Tc or voltage. All input should read on the first channel. So as per my wish, I can select the analog input. So that I can read the data and process and display it or send it out any one of the communication methods. similarly, I need 16 channels that can measure Universal AFE.

    https://ez.analog.com/data_converters/precision_adcs/f/q-a/163997/multiple-channels-with-ad4110-1/371491#371491 Similar application only I want.

    The target volume for this product is quarterly 1000 numbers. If it works error-free we can increase our target price again. This our initial target only.

    5) For the prototype I made one schismatic which is attaching below please go thought it.frist  two Channel I decided that 4-20mA or 0-10v application.3rd channel for RTD and fourth channel for a thermocouple. This is not made for universal input schismatic. just an R&D board only. To analyze the performance of AD7124 and its hardware components. If I make please tell me.

    SCHEMATIC1 - PAGE5.tif

    SCHEMATIC1 - PAGE6.tif

  • Hi 

    Thanks for your revert.

    If I use AD7124_8 and AD4112 then too costly right?. Because of this cost issue only I choose this AD7124_8 otherwise, I would have gone AD4112.

    Ad7124 and ad4112 if use also single-channel how can I configure. I need to use the separate input connector for AD4112 and AD7124.

     Please find out the attachment file. This block diagram for single-channel universal input.If I use AD7124_8/AD4112/1.Can I make two-channel universal analog input like the block diagram?.

Reply
  • Hi 

    Thanks for your revert.

    If I use AD7124_8 and AD4112 then too costly right?. Because of this cost issue only I choose this AD7124_8 otherwise, I would have gone AD4112.

    Ad7124 and ad4112 if use also single-channel how can I configure. I need to use the separate input connector for AD4112 and AD7124.

     Please find out the attachment file. This block diagram for single-channel universal input.If I use AD7124_8/AD4112/1.Can I make two-channel universal analog input like the block diagram?.

Children
  • 0
    •  Analog Employees 
    on Sep 3, 2020 10:14 AM in reply to heatcn

    Hi,

    I see that you mentioned the AD4110-1 application and also Jellenie recommended this device.

    Did you take into consideration to develop a board with a single universal input (modular design), but to have the option to connect/stackup up to four boards like this, with a different SPI address, on a single SPI bus (check-up figure 71 from AD4110-1 datasheet)?

    And if you want even more devices/boards connected, you will just need to switch between SPI busses.
    In this way you will be able to scale your system to your needs, you will have a smaller board with fewer IC components, fewer nonlinearities and errors, and at a lower cost.

    Regards,
    Mihai