How to create ampere control signal (4-20 mA) from voltage control signal (-10-10 V)

[newbieeng]

I have to control 4 proportional valves (Bürkert 2873 x 3 & 2875 x 1) installed on a gas line. These valves control signal type is 4-20 mA. I have a NI USB-X 6343 daq with 4 AOs of -10 - 10 V. How can I control these valves with this daq device? I am not familiar to electrics/electronics, that's why I am asking. Thanks in advance.

[crossrulz · Accepted solution]

That device can only output 5mA on the analog output.  So you will need an op-amp that can output over your 20mA.  See here for creating a converter circuit with an op-amp.  Your USB-6343 should be supplying the 1 to 5V to the op-amp.

[newbieeng]

Thank you crossrulz. I checked the page that you suggested. Is this circuit is enough to create 4-20 mA signal? just with a resistor of 250 ohm, and a transistor?

[crossrulz]

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@newbieeng wrote:

Thank you crossrulz. I checked the page that you suggested. Is this circuit is enough to create 4-20 mA signal? just with a resistor of 250 ohm, and a transistor?

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I is not a transistor.  It is an op-amp.  It will need an external power source (5 to 10V should do).

[AnalogKid2DigitalMan]

There are several commercial off-the-shelf solutions also, here is one example: http://www.dataforth.com/model.view.aspx?modelid=35 -AK2DM

[newbieeng]

Thank you AnalogKid2DigitalMan. They seem quite useful.