How to stabilize Voltage input

[JÞB]

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@Shah93 wrote:

Hi, I am facing the same problem right now that you were facing almost 4 years ago. I was wondering can you tell me how you overcame that problem. I am also a mechanical engineer like you and I am not too good in this stuff. Your help will be appreciated.

Kind regards,

Shah

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Shah, you really have not provided enough information about your problem.  Don't worry, it's a common enough problem that we have learned to ask good questions. 

I am going to bypass all of the preliminary questions and give you the information I missed pointing out to the original poster ( and left unaddressed by the replies)

Don't be afraid!  My magic 8-Ball is being consulted and has an extensive history of demonstrated accuracy. 

Current loops,  they are often used in physical environments where noise can be introduced.  They isolate the measurement by removing "ground" from the system and taking advantage of side effects of HOW current is measured by a DMM (read yor DMM's manual or Google it)  By the way, your handheld DMM has no connection to Earth Ground, your DAQ device does!  Your DMM measures average current over an apperature of time typically expressed in "number of power line cycles," or NPLC, and is inherently slower than a DAQ device A to D conversion.  It is naturally low-pass filtered.

So, you need to be careful about:

1. Keeping Ground out of your DAQ measurement system so as not to introduce the noise we avoided by selecting a current output sensor

2. Filtering or averaging a number of A to D conversions to duplicate that DMM measurement.

#1 is managed by using the correct AI input terminal configuration.  With DAQmx devices there are three options; single ended, non-referenced single ended and differential.   Ideally you would choose differential.  In some cases NSRE is acceptable but, some error is added.  Single ended is a poor choice and completely destroys any advantage we gained by choosing a current loop output sensor and then adds more sources for error.  Read the DAQmx help file or Google input configurations to learn more and why.

#2 is taken care of by post processing (analyzing) the AI channel data.  Taking the mean of every 1/60th of a second (1/50th outside North America) is common to remove power line noise.  Other noise sources can by filtered as their causes are identified by inspection. 

[Shah93]

Thanks for your kind response.

Apart from DMM measurement, I have connected the output wire of my transducer to another DAQ of Omega Engineering. The pressure values generated by that DAQ were quite stable. However, when I connect it with my NI DAQ (NI PXIe-1082) having card NITB-4300., the output values fluctuate significantly. The operating range of the transducer which I am using is: 4mA-20mA, 0-250 kPa. I am using the resistance of 250 ohms to acquire the voltage signal having the range from 1-5 V.  

I have a poor background in Electrical and Instrumentation. So, I apologize in advance for any stupid questions. I really need help here.

Kind regards,

Shah

[JÞB]

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@Shah93 wrote:

Thanks for your kind response.

Apart from DMM measurement, I have connected the output wire of my transducer to another DAQ of Omega Engineering. The pressure values generated by that DAQ were quite stable. However, when I connect it with my NI DAQ (NI PXIe-1082 having card NITB-4300., the output values fluctuate significantly. The operating range of the transducer which I am using is: 4mA-20mA, 0-250 kPa. I am using the resistance of 250 ohms to acquire the voltage signal having the range from 1-5 V.  

I have a poor background in Electrical and Instrumentation. So, I apologize in advance for any stupid questions. I really need help here.

Kind regards,

Shah

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They aren't "Stupid" they are "Ignorant" and you correctly asked for help understanding what you are unfamiliar with. 

Now, the TB 4300 is a breakout connector for a PXIe 4300 which has 16 single ended AI channels.  These channels can also be configured as up to 8 differential AI.  You really need differential!  You do this by by connecting the resistor between AI0+ & AI7+  (OR AI1-8, AI2-9...) and selecting "Differential" as the Input configuration for the AI Task.

Attach your VI and sample data, if you still have issues after correctly wiring and configuring your system.  We can be of greater assistance seeing what you see!  

[billko]

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@Bob_Schor wrote:

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@cbutcher wrote:

(as Bob Schor said, it might be related to your power supplies).

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Or, as my (formerly 3-year-old) daughter used to say, on submerging her ears in the tub and listening to herself talk, "Impedance mismatch!".

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That's my favorite thing to say when I cover my ears at work because I don't want to hear someone.  I see I have the same humor as a three year old.  And I'm fine with that.

[Shah93]

I am very grateful to you for your kind response.

This is the current situation of the card which I am using to extract data from the transducer. This setup has been provided by my senior to me and he told me not to worry about the complicated circuitry and you have to just connect the transducer with the DAQ only. Now, I am facing the problem and I don't have any background at all to solve this problem. Moreover, He is not being able to solve this problem as well😪. As I mentioned that I am not an Electrical guy so please ignore my incompetency related to this problem and kindly guide me what should I have to do to solve this problem.

Kind regards,

Shah

[JÞB]

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@Shah93 wrote:

I am very grateful to you for your kind response.

This is the current situation of the card which I am using to extract data from the transducer. This setup has been provided by my senior to me and he told me not to worry about the complicated circuitry and you have to just connect the transducer with the DAQ only. Now, I am facing the problem and I don't have any background at all to solve this problem. Moreover, He is not being able to solve this problem as well😪. As I mentioned that I am not an Electrical guy so please ignore my incompetency related to this problem and kindly guide me what should I have to do to solve this problem.

Kind regards,

Shah

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As I suspected, your photos show that you have miss-wired your Analog Inputs. You should be wired with the 250 resistor connected to AI0+ and AI7+.  The current loop would then flow from the sensor to AI7+ through the resistor to AI0+ and back to the sensor.   The DAQmx device must be configured as a differential channel for AI0 and will see the 1-5Volts differential potential across the resistor. 

Read the PXIe 4300 users manual for details.  

You might also look for online resources to expand your skills. The Navy Electricty and Electronics Training Series (NEETS) is available online and has self-paced modules that can be extremely useful for non electrical professionals when they need to learn about electrical measurements.

[Shah93]

Thanks a lot sir. I am very grateful to you for your guidance. I will try to fix this problem according to your suggestion.

Kind regards,

Shah