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Precision Amplifiers Forum
Precision Nanoamp current measurement
Hello, I am looking for a high precision amplifier to measure nanoampere currents. I am planning to use MSP430, I wonder which amplifier is convenient for this application. Is there an application note ? Thank you !!!
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.
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 !!!
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
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.
LMP91000 is right for this case, the bias voltage is programmable. pls find more information about this in specification Page 11.
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.
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.
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 !!!
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 ?
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 ?
i think the answer is YES.
why 5uA to 750uA input current is mentioned in the data sheet ?
- there is TIA unit in LMP91000, and the gain resistor is progrmmable, in other words the gain depends on the resistance.
5uA is the max current when the TIA gain resistor is 350Kohm, @min supply voltage.
750uA is the max current when the TIA gain resistor is 2.75Kohm, @min supply voltage.
wish it do some help.
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 ?
Can you explain wow you obtained these values ?
BIAS 8% VREF, it means 200mV
BIAS SIGN: negative
Internal Zero 67% VREF, it means 1.675V
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?
i want to measure AC current in the NANO AMPERE range and voltage is in KILOVOLT range.how can this be done ? actually i want a electronic circuit having a LED or someting which comes ON when this leakage current is present else OFF.PLS REPLY ASAP.
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