I need a DAQ which support 4-20 mA signals

[loghmani]

Hi

Which model of NI DAQ is suitable for 4-20 mA inputs?

[nitad54448]

hi

you mean read 4-20 mA ?

look in products and services/ c DAQ.. there are several.  the simplest cheapest have 8 entries 16 bit, there are also 24 bit (4 channels, three times more expensive and slower,... etc) you need to define what you need to do and the check on the webpage of ni.com (there are also 4-20 mA output, on 16 bit only, if I remember correctly)

N

[smercurio_fc]

You can also try calling your local NI sales rep.

[loghmani]

Yes, I mean reading 4-20 mA, I have some pressure sensors that their outputs are 4-20 mA.

I review ni  DAQ, all of them accept voltage as their analog inputs. how can I use these DAQ with 4-20 mA?

[AnalogKid2DigitalMan]

You could put a precision 250 or 500 ohm resistor across the input terminals of the DAQ and wire them to your 4-20mA signal.

Ohms law- 0.004A*250ohms will generate a 1V signal, while 0.020A would generate a 5V signal. Using a 500 ohm resistor it would double that range from 2V to 10V.

-AK2DM

[smercurio_fc]

You're not looking at the right thing. You need to find the modules that can measure current. Go to the main DAQ page (http://www.ni.com/dataacquisition/). On the left hand side under "Measurement Types" click on "Current" (since that's what you're trying to measure). There will be a number of products available. You can then filter based on what kind of form factor you can use.

An alternative is to use a precision resistor to convert the current to a voltage.

[loghmani]

Is using 250 or 500 ohm resistor to convert 4-20 mA to 1-5 V or 2-10 V an industrial solution? Is it accurate ? Won't be it a noisy measuring?

[nitad54448]

hi

i think it s better to use directly a current DAQ,.. why don't you look on the NI site ?  (as answered before.. ?)

N

[loghmani]

I know that using a DAQ which support is the best solution, but the problem is its price.

NI USB 9219 is suitable for this application, the price is 1249 EUR, but NI USB 6008 support voltage analog signals with 169 EUR.

I want to find a cost effective solution.

The other problem is that there is two 4-20 mA and three 2-10 V voltage signal in my sensors and I want to gather all of them

[RavensFan]

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@loghmani wrote:

Is using 250 or 500 ohm resistor to convert 4-20 mA to 1-5 V or 2-10 V an industrial solution? Is it accurate ? Won't be it a noisy measuring?

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Yes, it is an industrial solution.  That is inherently what a module that is designed to read current does.  It shouldn't be any noisier than using a current module to read current or a voltage module to read voltage.  Accuracy shouldn't be a huge issue.  The reason to use a precision resistor is that they are toleranced to a tighter resistance specification than an ordinary resistor.  Beyond that, you may want to run your own calibration routine so that you can accurately correlate a known current going in with the voltage that the DAQ device is measuring.  Apply 4 mA, read the voltage, apply 20 mA read the voltage.  Then you may find out your reistance is actually 499 ohms instead of 500 ohms and can account for that in your measurement conversions.