EVAL-AD5940ELCZ sensorPal Calibration Resistor

Hi 

I am using the EVAL-AD5940ELCZ with the sensorPal application. I am confused about the functionallity of the Calibration resistor in Cyclic Voltammetry.

I have noted that on the board the RCAL resistor is  value 200 ohms this is also the default value on the sensorPal GUI.

however if I leave it at the default setting I get a much higher current output than I would expect from my sensor  400 uA as opposed to in the range of  0 - 21uA

My settings:

initial potential  0mv

Final potential 1000mv

Step potential 2.148 uV (default)

Scan rate 100 mv/s

current range to 0uA - 21uA (85K RTIA) this is the range i expect.

Calibration resistor 200 ohm

Are the sensorPal examples only applicable for the on board dummy sensor or can custom sensors be used.

Do need to change the RCAL resistor if using a custom sensor.

I have noticed if I increase the calibration resistor value drastically (on the GUI only) the current output will drop to range that I would expect.

Also should step potential units on the GUI be in mV instead of uV  according to AN-1563 "The minimum step size is 537 µV on the AD5940"

Regards

Ian



Edit
[edited by: ian079 at 12:13 PM (GMT 0) on 5 Jun 2019]
Parents
  • +1
    •  Analog Employees 
    on Jun 5, 2019 4:17 PM

    Hi Ian,

    The calibration resistor is used to calibrate the internal Rtia on the LPTIA. SensorPal can be used for your own sensor also. Ensure jumpers JP9, JP10 and JP11 have disconnected the dummy network from the CE0, RE0 and SE0 pins. Are you connecting your sensor via the cables or wired directly to P7?

    RCAL should be chosen to be closer to the value of RTIA you plan on using to maximize accuracy of the calibration routine. I would suggest replacing RCAL with a 10k resistor on the evaluation board. 

    Yes, the units should be in mV. We will update.

Reply
  • +1
    •  Analog Employees 
    on Jun 5, 2019 4:17 PM

    Hi Ian,

    The calibration resistor is used to calibrate the internal Rtia on the LPTIA. SensorPal can be used for your own sensor also. Ensure jumpers JP9, JP10 and JP11 have disconnected the dummy network from the CE0, RE0 and SE0 pins. Are you connecting your sensor via the cables or wired directly to P7?

    RCAL should be chosen to be closer to the value of RTIA you plan on using to maximize accuracy of the calibration routine. I would suggest replacing RCAL with a 10k resistor on the evaluation board. 

    Yes, the units should be in mV. We will update.

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