How to display voltage and current synchronously

[shawn1]

Recently do a project about acquizeing voltage and current synchronouly ,then display. the design is welding a 0.5 ohm resistor(1%) in NI 6251 analog differential AI inputs, Then acquise the differential voltage at the AI input to convert to current. At the same time, I hope to grab the voltage of the analog input port. my issue is the current profile is no data. please help me .the program screenshot is show below. -------------------------------------------------------------------------------------------------- 1.may be you ask me why don't use no-dierential way to get voltage at all AI port, Then in software use minus to get the voltage at dierential AI inputs. this way will resolve my issue . i have a try ,but Current accuracy is fail. because my current expect range is 1uA~100mA. the samll current accuracy will not be promised if using single-way to acquise the voltage in NI 6251. NI 6251 Device spec(AI Absolute Accuracy) Nominal range(V) Absolute Accuracy(uV) Sensitivity 10 1920 112 5 1010 56 2 410 22.8 0.2 74 6.4 0.1 52 6.0 (i wanna use this range to measure samll current) ------------------------------------------------- Best regards Shawnh.Chen

[shawn1]

[crossrulz]

1. You should just have 1 task for all of your analog inputs.

2. Use the DAQmx scale to do the math for you.

3. Reading 1uA will be very hard with a DAQ, even with some external circuitry.  I recommend the TSC103IPT.  It is specially made for amplifying current shunts.  The output is a single ended voltage.  It also has a configurable gain.  But even with the gain of 100, you are only going to have 50uV for your 1uA.  I doubt the DAQ can be that accurate.  Still with the gain of 100, your 100mA will give you 5V to your DAQ.

[shawn1]

Thanks for your help.sorry for reply delay . get it, but I still have two confusion hope to get your reply 1.How to show the current waveform by accumulating 1 D Array data , Rather than show by every 100 acquisition points 2.What is the minimum identification unit of the amplifier TSC103IPT? I doubt that 0.5uA can be indentified?(0.5uV=0.5ohm*1uA) Because i didn't find anything about the auccary in TSC101IPT datasheet.

[crossrulz · Accepted solution]

---

@shawn1 wrote:
1.How to show the current waveform by accumulating 1 D Array data , Rather than show by every 100 acquisition points

---

Use a waveform chart.  Charts keep a history, so you do not have to accumulate the data.  It does it for you in the display.

---

@shawn1 wrote:
2.What is the minimum identification unit of the amplifier TSC103IPT? I doubt that 0.5uA can be indentified?(0.5uV=0.5ohm*1uA) Because i didn't find anything about the auccary in TSC101IPT datasheet.

---

The amplifier is analog.  So it can gain up anything.  But you really should think about using a larger resistor if you really want to measure that small of a current.

[shawn1]

Thanks Crossrulz. The measured current will be not accurate if i use a larger resistor (I have a try using a 1 ohm resistor to get the measured current 5uA ,but i try a 0.1 ohm resistor to get measured current 2uA. other example like this ). So i only just use a smaller resistor to reduce loading influence. Another question, You just kindly remind me to use a amplifier TSC103IPT.and said the amplifier is analog to gain up anything,but i doubt that The NI 6251 analog inputs is also analog ,why it can't gain up angthing? Haha.My question is so much .

[crossrulz]

---

shawn1 wrote:  but i doubt that The NI 6251 analog inputs is also analog ,why it can't gain up angthing?

---

The 6251 uses an Analog To Digital Converted.  That is what has a minimum sensing voltage.  That is also where the resolution specification comes from.

[shawn1]

Get it ,Thank you very much .