CN0359 conductivity sensor dev board: RS-485 header not outputting signal (always high)

Cell constant was calculated as 760/cm (while the maximum for the dev board is 100/cm). EXC voltage is 1.2

Datasheet: https://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0359.pdf

User-guide: https://wiki.analog.com/resources/eval/user-guides/circuits-from-the-lab/cn0359

Baud rate: 115200 bps

Address: 7

So on the J2 header, pin 1 and 3 are always high. 

2-electrode sensor is connected, and conductivity measurements are around 11.65 uS/cm

Any suggestions?

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  • 0
    •  Analog Employees 
    on Aug 23, 2019 2:04 PM

    Hi adamaero,

    I am trying to replicate what you're getting on the RS-485 signals. Are you trying to command the board through RS-485?

    Also, the rms voltage of the conductivity sensor output is 1.21V which is pretty close to the EXC voltage. The conductivity reading you got, 11.65 uS/cm, with a cell constant of 760 /cm is equivalent to 15.33 nS or 65.2 Mohms. Is this consistent with what you're trying to measure?

    The RTD is there for temperature compensation of conductivity measurements. The simplest way you can simulate one is using a 100 ohm or 1000 ohm resistor in 2-wire connection at pins 1 and 4 of J3.

Reply
  • 0
    •  Analog Employees 
    on Aug 23, 2019 2:04 PM

    Hi adamaero,

    I am trying to replicate what you're getting on the RS-485 signals. Are you trying to command the board through RS-485?

    Also, the rms voltage of the conductivity sensor output is 1.21V which is pretty close to the EXC voltage. The conductivity reading you got, 11.65 uS/cm, with a cell constant of 760 /cm is equivalent to 15.33 nS or 65.2 Mohms. Is this consistent with what you're trying to measure?

    The RTD is there for temperature compensation of conductivity measurements. The simplest way you can simulate one is using a 100 ohm or 1000 ohm resistor in 2-wire connection at pins 1 and 4 of J3.

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