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voltage to current conversion

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Lahari

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Hi,

I have a sensor which gives voltage output in 0-10v range. But I have no idea about its current range. I have a Data acquisition card which can take input only in 4-20mA current range. How do I convert the sensor output to this DAQ card input range?? How will be the connection? please help me by stating the diagram.
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Hi,

I have a sensor which gives voltage output in 0-10v range. But I have no idea about its current range. I have a Data acquisition card which can take input only in 4-20mA current range. How do I convert the sensor output to this DAQ card input range?? How will be the connection? please help me by stating the diagram.
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hi,
This is one option for a 0v thru +10V input to 4mA thru 20mA output

EDIT:
If you would prefer a single IC solution the AD694 is OK, I have used it in the past.
 

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Hi Strantor,

Thank you for your reply. I have gone through what you have suggested. But actually I want to do something by my own. Isn't there any simple solution?
 
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Hi ericgibbs,

Thanks a lot for your reply. Your suggestion is enough for my requirement. Thanks again.
 
This is one option for a 0v thru +10V input to 4mA thru 20mA output
Eric, to be a true current source the acquisition card load must be connected between +V and Q1's collector. The schematic shows R6 as a load but that resistor is just to establish the current value which appears at the collector of Q1.
 
Eric, to be a true current source the acquisition card load must be connected between +V and Q1's collector. The schematic shows R6 as a load but that resistor is just to establish the current value which appears at the collector of Q1.

Carl,
Most of the 4-20mA receiver PCB's I have used have an internal load resistance of 250R and I have used this voltage to current method without problems.

Without knowing the OP's actual termination resistor I have had to assume its 250R, if he comes back and says what the termination resistance is, I will modify the circuit.

I have also had to make the assumption that the 'low' side of his receiver is at 0V.

I suspect the OP will find the AD694 easier to build.

Lahari.
Perhaps you will let us know what the load details are and which option you have chosen.
 
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Carl,
Most of the 4-20mA receiver PCB's I have used have an internal load resistance of 250R and I have used this voltage to current method without problems.
Eric,

You may have used it without problems but for that method the accuracy is affected by the line resistance and any other resistance in series with the load. The purpose of a current loop is to have the current (and accuracy) unaffected by those variables and why a true current loop driver is constant current.

Your scheme is really a constant voltage circuit at the source. To be a true current converter you must put the load in the collector circuit as I stated. This can be done if the driver power supply ground is isolated from the receiver ground.
 
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Carl,
We dont know.
The line resistance.
The load resistance.
The supply voltage.
Are the 0V to 10V source and/or the V2C supply isolated from the DAQ ground, dont know.?

From the little we do know, I would not expect the V2C pcb to more than a few inches away from the DAQ pcb, especially as the Source is a 'remote' 0V thru 10V, which I would expect to be the long run.?

If its a long run, I have a more suitable, but more complex circuit for the OP.

I know that its not a true current loop, its a Voltage to Current Converter located I think at the DAQ input.

I would with respect Carl, suggest that you post your version of the circuit instead of taking pot shots at mine.:D
 
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..............
I know that its not a true current loop, its a Voltage to Current Converter located I think at the DAQ input.

I would with respect Carl, suggest that you post your version of the circuit instead of taking pot shots at mine.:D
I'm sorry if you took what I said as a pot shot. That was not my intention.:eek: I (thought) I was just observing that your circuit has a constant-voltage not constant-current output.

Usually the 4-20mA current generator is located close to the sensor and the long line is the current loop since it is insensitive to voltage noise pickup and the effects of line resistance. Thus my comment about the line resistance. If the current generator is close to the receiver, then obviously my concern is groundless and your circuit would work fine.

My previous suggested solution was to use the collector of the transistor in your circuit as the current source. The only requirement is that the source power supply be isolated from the receiver power supply. If that is not possible, then a more elaborate circuit would, of course, be needed.
 
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hi Carl,
This is a simplified variation of the AD694, it still has the DAQ input as 0V. [as does the IC itself]

If the OP can get a AD694 that IMO would be the easiest build.

Eric
 

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Hi Eric & Carl,
Thanks to both of you for clarifying the idea. But I want to use AD694. I have searched it in our local market, but did not get it. Any other solution like a simple IC?
 
Hi Eric & Carl,
Thanks to both of you for clarifying the idea. But I want to use AD694. I have searched it in our local market, but did not get it. Any other solution like a simple IC?

hi,
Whats your location.??

You could build that simple circuit in post #11.
 
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