in cn0359,what input voltage and frequencies are applied for corresponding conductivity ranges and in four electrode method how to connect resistors in cn0359 evaluation board
Hi dhanalakshmi: the CN0359 both excitation voltage and frequency can be set in the menu. please see the sensor datasheet for the voltage and frequency range can be apply. the CN0359 conductivity sensor terminal have 5 pins, please make sure you shorted pin1 with pin2 and pin3 with pin4 (pin1 is close to RTD terminal), connect the simulate resistor (100Ω~10kΩ is good for simulate) to the pin1<->2 pair and pin3<->4 pair like figure 1 in circuit note.
I tested the board EVAL-CN0359_EB1Z with a 2-wire probe or resistors, and the proof is very satisfying.
I noticed that the excitation voltage that you can set in the menu is the maximum value that reaches the voltage on the probe when the conductivity varies.
Instead the frequency never changes and remains on the set value.
I have also made some tests with a probe with two wires (K 0.0989) and the card works very well, in the solutions that I have, but I have a problem with a 4-wire probe with 0.7 k, it always tells me the probe is incorrect.
The only parameters to be set are the temperature compensation (which I disabled) voltage and excitation frequency.
I modified these values, but the answer is always “incorrect probe”.
Why does it works correctly when I shortcut pin 2 to pin 1 and pin 3 with 4, also with the probe connected, while if I connect the 4-wire probe as specific I always get “probe incorrect” even if I change voltage and frequency of excitation? (I tried the whole voltage and frequency range).
I inserted a 100 Ohm resistance between pins 1 and 2 of J5 and another 100 Ohm resistor between pins 3 and 4 of J5, keeping my 4 wires probe connected.
It is no longer giving reading error, but the probe reads with a 10% error between 80uS and 200mS.
Taking a look at the scheme it does not seem a good solution because I'm distorting the geometry of the probe. Do you have any other ideas for me?
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