IV characteristics not coming correct with cd4051 mux

[jyot445]

 hello,

i am using mux-4051 to get the IV characteristics.for testing i have 1K ohm resistor but by the slope measurement its not giving correct resistance value.can anyone help me in figuring out why is it coming like this.

* table.png:snippet of the whole program (with keithley 2420)

*front panel.png: snippet of the IV ccurve(for 1K resistor) 

[cstorey]

I'd suggest that:

1) Source current and measure voltage. ** 

2) Look for possible ground loops in your circuit.

3) Use 4-wire (Remote sense mode on K2420).

** If you source current thru the resistor and measure the voltage across the resistor, then you can be sure that the measurement is accurate.  But if you source voltage (developped at the meter, before the wires/connectors/mux/resistor) then you cannot be sure that the resistor you want to test actually has the right voltage across it for the current you are measuring.

Craig

[jyot445]

@cstorey

hi,

Thanks a lot for the reply.

problem is:

1.i can't source current and measure voltage as i have to design this program for solar cells(6cells) in which my PI has said to make voltage only as the input control.

2. i checked for ground looping,from ports which i have given 0(usb-6501) are actually having voltages in mV.Is this thing creating any difference in measurement?

and inhibit ,Vee are also having 0.357 mV voltage which are grounded.

3.4-wire is used when i am getting extra resistance.but here the IV graph is itself not correct.

do you think there is leakage current from mux?

[jyot445]

is there something else(device/circuit)through which i can do TO multiplexing of pervoskite solar cells in labview.?

PLEASE HELP

budget:15000 INR.

[cstorey]

Ok, now I remember you're previous questions.  I thought you just wanted to measure resistors here and were getting funny results.

Have you tried other larger resistors?  1M, 10M?  Perhaps the MUX is acting as a voltage divider or has a not some non negligible internal capacitance.  You'd have to go through the specs carefully.

Personally, I'd suggest buying a switch matrix and MUX card compatible with SMU measurements.  Keysight and Keithley make a wide array of switches for semiconductor testing..

- https://www.tek.com/keithley-semiconductor-test-systems/keithley-700-series-semiconductor-switching-...

- https://www.keysight.com/en/pc-0000100020019%3Aatg%3Apgr/low-leakage-switch-matrix-family-b2200a-b22...

Just characterize some of your solar cells individually.  Figure out their parameters (leakage current, impedance, etc..) then select a MUX or switch to match those parameters. 

Craig

[jyot445]

@cstorey

thanks a lot for this, I am going to perform these things first(some characterisation)& will see its other parameters to choose the matrix mux.

THANKS

(will need you people if get stuck somewhere)

Jyotsna

[jyot445]

can i use ni usb-6525 for 4 solar cells as it has a solid state relay switch?

thanks

[cstorey]

Hi,

I looked at the specs for the CD4051 MUX and the Ron is minimum 125 Ohms, max 1300 Ohms.  Also the max current you can pass through the MUX is 10mA.  Does that meet your needs?

Have you tried measuring a bigger R?  What sort of curve do you get?

The NI-6525 is a Digital I/O card.  I don't see how it will help, unless you use it to control relays for each solar cell.  There are cheap relay cards out there, perhaps better suited to the task than the MUX you've chosen - https://www.robotshop.com/ca/en/5v-4-channel-solid-state-relay-ssr.html?gclid=Cj0KCQjwidPcBRCGARIsAL...

[jyot445]

hi cstorey,

I tried with higher resistance its adding 200 ohms extra to the actual resistance(for 2.1k).

the solar cells has its resistance in between 120-160 ohms,and the mux resistance would be min. 150 ohms;so obviously it will alter the IV characteristics we want (thats actually coming without MUX).

 In the link of the SSRs,what min. resistance do they poses (is it in milliohms)cause i could not find it in the datasheet or anything.

Ni usb-6525 has been used for four solar cells in CSIRO ,Australia.

Thanks

[jyot445]

hi,

@cstorey 

"The NI-6525 is a Digital I/O card.  I don't see how it will help, unless you use it to control relays for each solar cell."

It has got 8 channel to channel insolated output channels as SSRs.

and i got this thread:

https://control.com/thread/1026147135

can you please help me now why i can't use it as a relay