how to amplify the input signal using LabVIEW 8.6?

[Manjukb15]

1) With the input voltage say 0.1mV through DAQ into the LabView, can anyone tell me how to design a circuit in LabVIEW 8.6 to amplify the input signal.

2) When i applied 0.1mV, there were noise signals in the LabVIEW Oscilloscope. Can you tell me also about the noise reduction circuit for the above voltage?

[simply_me]

So it really depends what you are trying to do....

For amplification, if you want to use plot something, you can just multiply all of your measurements by a scalar (say 10).

I'm not an expert on SNR with NI scope,but I've used LV filters before to eliminate unwanted signal/noise.

Hope this help,

A 

[Buechsenschuetz]

Of course a scalar multiplication by software is NOT the same as amplyfing a signal. When using software multiplication of signal strength you do not increase resolution and s/n ratio. You may see your signal expanded to the full bit range of the DAQ but of course resolution is determined by the analog input range of the DAQ. 

Usually DAQs do not use any kind of noise reduction, since the designer of the DAQ does not know which signal will be connected to the DAQ and which frequency range is needed by the user. If you have a signal with low output impedance (and proper wiring, of course) there will be little noise on the input.

[Meadow]

Hi Manjukb15,

1. May I know which model of DAQ that you are using? Some DAQ allows you to define the expected signal range into the DAQ (+/-1V or 2V or 5V or 10V, etc - based on the specification of the DAQ device). With NI DAQ device, in DAQmx Configure Acquisition, you can define this input range and DAQmx driver will automatically amplified the input signal to maximize the resolution of the ADC in the DAQ device.

2. What do you mean when you applied 0.1mV signal? Are you putting in a known source of 0.1mV Signal into the Oscilloscope (NI Digitizers) from a function generator? What kind of noise reduction circuit that you are expecting to be in the scope? Any particular model of NI Scope/Digitizer that you are using?

Regards

[Manjukb15]

The DAQ model I am using is NI 6115S with the terminal box of BNC 2110. Do you have any idea, that this DAQ has any provision to set the input voltage range.

I am putting the output voltage from PMT which is in the range of 0.05mV to 0.15mV.

Does the above DAQ model detects this low voltage? If its possible how i can detect and amplify the signal?

Does it require any noise reduction circuit to be connected in the VI with the DAQ, for this low voltage to detect the required output signal?

[Buechsenschuetz]

Concerning the PMT signal, what kind of circuitry are you using between the PMT and the DAQ? Usually the PMT output signal is a currant source (with very high output impedance) which should not be connected directly to a DAQ. The signal usually is converted to a voltage source with a current-to-voltage converter (transimpedance amplifier). A very simple method is to use a (rather high) resistor in parallel with the DAQ input but this method may affect the operation of the PMT (since the voltage between the last dynode and the anode will not be constant). 

However, in case you are using any of the usual method to convert the PMT output current into a voltage, the voltage levels you mention seem to be very low.  

[Ankur Jain]

As per the S series multifunction DAQ specifications for NI PCI-6115, the minimum input range is +0.2 v , -0.2 V.

Minimum Voltage Range Accuracy 390 µV 
Minimum Voltage Range Sensitivity 0.098 mV

The input voltage that you are planning to acquire (0.1mV) is just at the sensitivity level and thus will be accompanied by lot of noise. Please amplify your signal before using the DAQ device. 

[Buechsenschuetz]

I still wonder why the PMT has such a low output voltage - and why a VOLTAGE, not a current...

PMTs are current sources, and the current flowing from the anode has to be converted into a voltage. If you simply use the input resistance of the DAQ as "current-to-voltage converter", the signal should be much stronger, it should read in the 1V or 5V range (and even much more if you expose the PMT to daylight, so take care for overvoltage protection!). Only thing I can imagine is that you just measure the dark current (i.e. current wihout ANY light - PMTs are very sensitive and virtually see EVERYTHING) or the voltage related to that dark current which actually will be very low.

Again, except when you are trying to detect VERY low light levels, the voltage you measure across the input resistance of the DAQ seems very low for an exposed PMT.  

[quixomniac]

Hello,

I am also running into similar issues.
I was wondering if a circuit was ever proposed.
I am working with a Load Cell with the typical wheatstone bridge
with an NI PCIe-6321 trying to get in a 0.1 mV signal.
A little web browsing lead me to a differential amplifier

http://www.electronics-tutorials.ws/opamp/opamp_5.html

However, I'm not sure if this would work with my lack of experience in electronics,
nor do I know  which type of op-amp to get.

[Buechsenschuetz]

First, if you never have designed any electronics yourelf, a differential (instrumentation) amplfifier is not a project for beginners. You should have at least some basic knowledge about operational amplifiers and their application.

Second, there are off-the-shelf devices which will probably fit your application, like this one:

http://labjack.com/catalog/ei1040-dual-instrumentation-amplifier

http://news.thomasnet.com/fullstory/Instrumentation-Amplifier-targets-DAQ-applications-562207