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aale2025,

We can be of greater assistance if you could provide some more details. Can you tell us the source of the current you want to measure? Polarity of the current? Bandwidth? Power supplies available? Any type of additional details might help us suggest a suitable circuit and amplifier.

Regards, Bruce

Hello Bruce,

Thank you for your response.

The source of the current is a 3 electrode sensor, onto which a liquid sample drop is positioned. Then, a reactive is added, and after around 320 seconds, current is measured. The current may vary between 0 to 1000 nA. The electrodes must be polarized with -200 mV, for taking the current measurement.

The power supply will have to be built.

The idea is to take the current measurement, and display it on an LCD, and also transmit the current-time curve to a PC via USB.

I am planning to use one of the MSP430 family, for which I have already bought the programmer.

This job is for the University of San Juan, for the chemical lab. By measuring current, under the previous conditions, students can determine whether the sample has toxins or not, and if so, its level.

I am attaching a typical graph.

Thank you !!!

Regards,

Alejandro

Alejandro,

Even I cann't see the figure you post, i do believe what you are dewaling with a electrochemical sensor. if it is true, strongly recommend you consider LMP91000.

it is a highly integration analog front end solution for this kind of application. wish it helps.

for more information, pls visit below link. http://www.ti.com/product/lmp91000

reagards

Hawk Tong

Dear Tong,

Thank you for your email. Is there I way I could send you the image ?

Does the LMP91000 can sense currents in the nanoamp range ? Also can the LMP91000 polarize two of the three electrodes to 200 mV ? I need to implement a potensiostat.

Thanks again,

Regards,

Alejandro

Dear Hawk Tong,

Is there an AFE chip like LMP91000 with a high precision ADC built in ?

I found LMP90100, but it seems not suitable for a 3-electrode quemical sensor.

Thanks again,

Alejandro

At present, there is such a part, eletrochemical analog front end plus ADC but LMP91000. my suggestion is to consider LMP91000 + MSP430F2013 / MSP430AFE251.

wish it helps.

Best regards

Hawk

Hi !!!

LMP9100 datasheet claims conversion of current ranges from 5 uA to 750 uA full range… I wonder if it is possible to measure currents within the range 0 – 1000 nA. Thank you !!!

Sir,

1. per your input, i am checking with my colleague. and will give you a confimation soon.

2.  i am not sure what is your end application, electrochemical sensor, pH probe, or other similar application.

     may i know backgroup of your case ?

regards

Hawk

Dear Tong,

Thank you for your email.

The end application is an electrochemical sensor. The objective is to detect the presence of ochratoxin in food samples. An electrochemical sensor is used for that purpose like the one shown in the following picture:

The sensor is interfaced to a potensiostat for current measurement.

A liquid sample drop is positioned over the sensor strip, when that happens the current curve drops rapidly. I need to sense that current drop and the ongoing current values until the current reaches stability. That current measure provides the information of ochratoxin presence. If the current drops more then, there’s no toxin in the sample.

In the next picture, stability is reached around 350 seconds.

The electrodes must be polarized at -200 mV for the experiment.

I intend to use a MSP430 microcontroller, a potensiostat (possibly the LMP91000), acquire the current curve, display the current stable value on an LCD display, and send the curve via USB to a PC.

This is for my electrical engineering thesis, at Universidad Nacional de San Juan, to be used at the biochemical student lab at Universidad Nacional de San Luis.

Looking at the picture, current range measurement is 0 nA to 1000 nA.

What do you think ? Is it possible with LMP91000 ?

Thank you.

Best regards,

Alejandro

Dear Tong,

Thank you again. Indeed your help is appreciated.

So, if I choose the TIA gain resistor 350Khom, would I be able to measure currents 0-1000 nA ?

Regarding, the instrument sensitivity, datasheet says for gas applications 0.5 nA/ppm to 9500 nA/ppm, could I expect 0.5 nA sensitivity for my amperometric application ?

Thanks again,

Alejandro

Dear Domenico,

Can you explain wow you obtained these values ?

VDD=3.3V

VREF= 2.5V

BIAS 8% VREF, it means 200mV

BIAS SIGN: negative

Internal Zero 67% VREF, it means 1.675V

RTIA=350Kohm

Thank you !!!

Dear TI member,

It's possible to work with a another TIA gain other 350Kohms?

In my application i need to go 1.2 Mohms, it's possible with no problem for the OPA TIA mesurment?

Thank you for your response.

BEN