Does AD5933 Rev.C evaluation board & Tools can measurement the frequency sweep 1HZ ~ 100KHZ from the RFB & Z(R or C) value?
The circuit itself should be capable of measurements you describe, perhaps with diminishing accuracy below 10KHz due to "DFT" artifacts. Still unclear what the transistor is for - the OPAMP should be capable of producing enough current for your measurements.
Sensor picture does not help much - it is not clear what the OPA_OUT3, VREF and OPB- nets are connected to."Transducer" and "Readout Circuit" boxes inside some "CMOS IC" can mean pretty much anything. Perhaps you need to find somebody deep into the subject to be able to guess.
The system clock (MCLK) should be scaled in order to have a sweep lower than 5kHz.
Table 2 on page 20 of this user guide shows the scaled system clock and its corresponding frequency sweep range.
Hi Mark :
Thanks for your feedback,
One question, If I need frequency range increases from 1HZ ~ 1KHZ that AD5933 Rev.C evaluation board & Tools can work?
Best Regards Uni Ting
Hi Uni Ting,
No.With the 16MHz crystal reference clock onboard. The frequency sweep would be from 5kHz to 100kHz.
I've tried generating frequency sweep from 1Hz to 1kHz with the evaluation board but the evaluation software just crashes. Also, I tried generating frequency sweep from 10Hz to 1kHz but the measurement is incorrect.
Using a lower reference clock for the board would decrease the lower limit for your frequency sweep but it also decreases the upper limit. Also, it takes the AD5933 longer to return the impedance results due to the slower ADC conversion clock speed.
I'm very kindly thanks for you reply!
I'm have project to Body Surface Impedance Measurement, but need measure low frequency as you know 1HZ ~ 1KHZ!
Do you have any good ideal to study it or use AD5933 and other IC to support AD5933 could be worktable.
Best RegardsUni Ting
You may consider looking through this thread.
Hi Snorlax :
Thanks your recommend, if I could use simple measure frequency between 10kHZ and adjustment AD5933 Z = R+C, RFB = 200KHZ, It's can be work as below waveform?
Could you clarify your question?
1. Did you mean RFB = 200 kiloOhms?
2. Did you mean Z = R + C to be R like a sequential RC network?
3. What are the expected values of R and C?
4. What is your Vout voltage setting?
Yellow rectangle on the picture covers range from 1KHz and 100KHz. If you need to scan frequency below 10KHz it will be necessary to either physically divide MCLK frequency or get into a rather cumbersome mathematics.
Thanks for your quickly feedback, pls see as below reply :
3. Z = R + C, expected values R = 200K,C = 1nF.
Other : I plan to try scan frequency 5kHZ ~ 100KHZ. Because scan frequency topic is 10khz.
Regarding #3, could you please take a look at this page: on the left there are two RC circuits, which one is of interest to you the one at the top or the one below it?
The impedance shown on your picture probably corresponds to something more complex than just an RC circuit. Is it from some measurement cell for liquid samples?
1. I would use : Series: ZS = R [1 + (jω/ω0)] / (jω/ω0).
2. Yes ! I need simulation liquid samples impedance use item 1 formula for R+C between frequency 10kHZ
1. Values R = 200K,C = 1nF will give you characteristic frequency of about 1KHz , so at 10KHz and above the network will behave mostly as a resistor only.2. If the liquid is some aqueous solution, 2Vp-p will cause electrolysis. Depending on solution composition even using the lowest setting (see Table 1 on p.3 of this application note) may cause measuring cell to respond a bit non-linearly.3. The manufacturer suggests choosing RFB according to the formula on p.5 of the same application note.
I used Z = R+C =10K+1nF, RFB = 10K to simulation frequency about 10KHz!
Result : Does it's good for my simple liquid measure for 10khz
It looks like the circuit behaves as it is supposed to for the component values you listed. It is hard to say whether the RC network you measured is representative of your liquid cell: the equivalent values of R and C will depend on liquid composition and cell geometry and can be much higher or lower. Since you use 2V p-p excitation, please see my earlier message re electrolysis. And re the choice of PFB value.
Good day! this is my SCH for EIS measurement for test frequency(10kHZ), could it ok?
RFB : 120K / MCLK = 1KHZ / I2C CLK = 1KHZ, Z = 110K
Not sure what this circuit is supposed to do, so cannot answer your question. What is the purpose of the transistor? There is no closed feedback loop for the first OPAMP and no overall negative feedback. -IN_A input seems to be hanging in the air, what is this test point TP1 connected to, if anything?
It would probably make sense to review the AN-1252 application note, especially the circuit on Fig. 4, figure out how it works and may be reproduce on a breadboard.
This is reference three electrode measurement page, to Calculation liquid Impedance change.
Update three electrode.
Makes more sense now. What is the nature of the sensor, can you send a reference where this sensor is described? Is it an electrochemical cell of some sort?
Still unclear why you would need a transistor there: AD860x OPAMP max output current is 30mA and your min sensor resistance is 200 Ohms. R6 should not be 0 Ohms.
You're right! RFB = 747ohm. Does it can be measure frequency limited from 5k~100k hz
sensor look like below behavior :
Retrieving data ...