application of current output & voltage output of a sensor

[R.V.]

hiii.......my question is that we have two types of sensor output. one is current & other is voltage. can someone specify which is the particular application where we use a sensor having current output only & in which application we use a sensor having voltage output only?

Pls reply soon.....

[R.V.]

i want to know one more thing is what is difference between update a control value using a local variable & its property node "value"...........

[RavensFan]

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@R.V. wrote:
My question is that we have two types of sensor output.  One is current & other is voltage.  Can someone specify which is the particular application where we use a sensor having current output only & in which application we use a sensor having voltage output only?

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We can't answer that.  You haven't told us anything about your sensors or your application.

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@R.V. wrote:
I want to know one more thing is what is difference between update a control value using a local variable & its property node "value"...........

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Search http://forums.ni.com/t5/forums/searchpage/tab/message?location=forum-board%3A170&q=local+vs.+propert...

[R.V.]

hiii......ravens .......actually this is my question...i want to know the application. one interviewer ask me this question..you can assume any sensor.  like pressure sensor where we get output 4mA to 20mA but specify the application. so my question is in which application we can use only a sensor which has only current output?

[RavensFan]

Please capitalize your sentences properly so they are easier to read.

There is no particular reason to use a current based sensor over a voltage based sensor in any particular application.  It is kind of a backwards question.  The question should be what is it you are trying to do, then what are the sensors available for that particular measurement.

A 4-20 mA current based sensor has the advantage of having a 0 mA signal coming in meaning something.  A disconnected signal wire.  You don't get that advantage with a voltage based sensor where a  0 V signal is a valid measurment in normal operation as well as a possibly disconnected wire.  Current based sensors are not generally sensitive to voltage drop due to current flowing in the wires, but there is a limitation to the resistance of the entire loop.  A voltage-based signal could change due to current flow in a high resistance wire thus showing a lower voltage at the data acquisition end of the wire compared to the source of the wire.

[mikealder · Accepted solution]

In a noisy electrical enviroment the current drive for the signal is less prone to picking up noise when compared to a voltage level signal, as RF has pointed out the 4-20mA signal is very handy for troubleshooting when a wire is disconnected - Mike